Climate Change / Global Warming

[MoghLiechty2]

Figures 4 and 6 from the summary for policy makers from the 2007 4th report by the IPCC (pdf here) show location-specific predictions for temperature change due to anthropogenic forcing. We don't expect that temperature change from anthropogenic greenhouse gases will be the same across the planet, and this variation is therefore part of the problem. Yes, the North Poles are expected to warm a lot, and land is expected to warm more than the ocean. This is important, and this will have effects on ecology and on human infrastructure. Pretending that only 0.6 degrees of local warming is due to anthropogenic climate change is misleading and factually incorrect.

It's definitely possible that 'anthropogenic forcing' can have a greater than 0.6 degree effect on local climates. However, if you're going to attribute a greater than 0.6 degree effect to any particular climate, you can't subsequently claim that other local areas that receieve neutral temperature effects result from non-antrhopogenic forces. In other words, the average anthropogenic forcing temperature difference is still 0.6 degrees, and the article is still heavily relying on models to attribute this 0.6 degrees to human activity.

More importantly, the conclusion that local variations can be magnified effects of greenhouse gases is one of the weaker statements made:

It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica (see Figure SPM.4). The observed patterns of warming, including greater warming over land than over the ocean, and their changes over time, are only simulated by models that include anthropogenic forcing...

Difficulties remain in reliably simulating and attributing observed temperature changes at smaller scales. On these scales, natural climate variability is relatively larger, making it harder to distinguish changes expected due to external forcings. Uncertainties in local forcings and feedbacks also make it difficult to estimate the contribution of greenhouse gas increases to observed small-scale temperature changes.

Natural local variations are nigh impossible to weed out in the real world, I can only imagine the difficulty in a simulated model. And of course the only model that has major local variations is the one where you include variables that we haven't directly observed yet. I swear, as I read these articles, I become less and less inclined to accept these models as able to accurately predict future conditions.

[Enuja]

People do look at the effects of local temperature changes on ecology and the like. The local temperature changes are facts, while the correlation between the local temperature changes and the local ecology require multiple areas with variation in both local temperature change and local ecology changes. When experiments reveal mechanisms that would make ecology change in predictable ways due to a given temperature change, we can say that we've supported the theory that the local temperature change caused local ecological change. It's much more problematic to say "this local temperature change was caused by anthropogenic global warming". So, instead we say that the we're warming the earth, and these sorts of changes occur due to warming, so we'll expect to see more of these sorts of changes as the earth warms. That's real. The presence of uncertainty does not mean that anthropogenic global warming is not changing the real world you live in. Local cooling in the recent past has actually also been really useful to show how local ecologies change with temperature change.

More importantly, the conclusion that local variations can be magnified effects of greenhouse gases is one of the weaker statements made

This is an inaccurate statement. What we can't do yet is make well supported predictions for temperature changes on small scales. We can make well supported predictions for temperature changes on large (continental and some smaller) areas, and we can also say that there will be local variation in temperature. The problem is predicting a specific temperature, or saying that a particular temperature change is due to global climate change. The problem is not saying that there will be local changes due to global climate change. That's a logical truism as long as there is global climate change.

[Dr._Orion]

I have had to do a fair bit of research on global climate change for school (Debate Team), and I found some interesting possible effects of rising CO₂ levels. This is only the stuff off of the top of my head, i will have to dig all of it out later.

1. rising CO₂ can cause famine not only due to climate change, but additionally, as plants thrive off of CO₂, it will induce greater plant growth. The problem being however, this will impact weeds much more than most other plants, This will cause weeds to grow more competetive and ruin both ecosystems and possibly crop yeilds. If weeds choke out other producers, the ecological damage could also cause shock waves that haven't been experienced before in human experience, we have seen the extinction of animals, not plants.

2. I also read a couple articles that global warming may cause global cooling due to melting glaciers (already covered).

3. I need to check this again, but I think there were something about the disruption of the current coming from the tropics past California (can't remember its name) that would be disrupted also, and would essentially plunge the Western part of North America into its own minirature Ice Age.

[EdgarJPublius]

I have had to do a fair bit of research on global climate change for school (Debate Team), and I found some interesting possible effects of rising CO₂ levels. This is only the stuff off of the top of my head, i will have to dig all of it out later.

1. rising CO₂ can cause famine not only due to climate change, but additionally, as plants thrive off of CO₂, it will induce greater plant growth. The problem being however, this will impact weeds much more than most other plants, This will cause weeds to grow more competetive and ruin both ecosystems and possibly crop yeilds. If weeds choke out other producers, the ecological damage could also cause shock waves that haven't been experienced before in human experience, we have seen the extinction of animals, not plants.

highly unlikely, Commercial crops are well cared for and I doubt any advantage this effect could yield to weeds is not actually that great compared to how advantageous an environment a commercial farm is to food crops. Not to mention that many weeds are themselves edible, so even if they do miraculously manage to outcompete the food crops, the famine would be mitigated somewhat (yes, I am aware that edible weeds don't generally provide nearly as much nutrition as most food crops or we would grow weeds as food crops too.)

2. I also read a couple articles that global warming may cause global cooling due to melting glaciers (already covered).

there are a huge number of feedback loops in the environment which can lead to global warming or global cooling, that's one reason climate prediction is such an iffy proposition, modelling all the feedback loops and their interaction is a pretty intensive operation, and It's entirely likely that there are feedback loops in effect we aren't even aware of.

3. I need to check this again, but I think there were something about the disruption of the current coming from the tropics past California (can't remember its name) that would be disrupted also, and would essentially plunge the Western part of North America into its own minirature Ice Age.

[/quote]
The has already been brought up, the research behind thermohaline currents shutting down due to climate changes is a fairly controversial topic from what I can tell.

[SummerGlauFan]

I have had to do a fair bit of research on global climate change for school (Debate Team), and I found some interesting possible effects of rising CO₂ levels. This is only the stuff off of the top of my head, i will have to dig all of it out later.

1. rising CO₂ can cause famine not only due to climate change, but additionally, as plants thrive off of CO₂, it will induce greater plant growth. The problem being however, this will impact weeds much more than most other plants, This will cause weeds to grow more competetive and ruin both ecosystems and possibly crop yeilds. If weeds choke out other producers, the ecological damage could also cause shock waves that haven't been experienced before in human experience, we have seen the extinction of animals, not plants.

This is a drop in the bucket compared to the possible changes in weather patterns and other environmental changes.

2. I also read a couple articles that global warming may cause global cooling due to melting glaciers (already covered).

3. I need to check this again, but I think there were something about the disruption of the current coming from the tropics past California (can't remember its name) that would be disrupted also, and would essentially plunge the Western part of North America into its own minirature Ice Age.

Both of these are related, as melting of glaciers (particularly the ones in Greenland and Antarctica) are going to play havoc on ocean salinity, which is where the current disruption comes from. Whether or not that would lead to anything like a mini Ice-Age is controversial, to say the least. It would not likely be a good thing, however.

I'm sure it's been brought up in this thread before, but if the oceans warm enough to thaw the frozen methane deposits, especially the ones in the Pacific, we're in for a really bad time. Methane is far, far more dangerous than CO2 warming-wise, and I have read convincing arguments that, at least in the short term, it would make the atmosphere explosive.

[Comic JK]

Methane is far, far more dangerous than CO2 warming-wise, and I have read convincing arguments that, at least in the short term, it would make the atmosphere explosive.

Methane-air mixtures will not burn at all until they are at least 5% methane. Enough methane to constitute 5% of the mass of the atmosphere is...not going to happen. The concentration of methane in the air currently--which is too high, for global-warming purposes--is only 2 parts per million.

[EdgarJPublius]

I'm sure it's been brought up in this thread before, but if the oceans warm enough to thaw the frozen methane deposits, especially the ones in the Pacific, we're in for a really bad time. Methane is far, far more dangerous than CO2 warming-wise, and I have read convincing arguments that, at least in the short term, it would make the atmosphere explosive.

if the ocean warms that much, we're pretty much screwed anyway.

That's the problem with a lot of these 'runaway feedback loop' scenarios, we'd already have to be eyebrow-deep into worst-possible-case territory for most of them.

[Vaniver]

I was under the impression that methane clathrates (that's what you're talking about, right?) were raised and then dismissed as a runaway feedback loop.

[SummerGlauFan]

Methane is far, far more dangerous than CO2 warming-wise, and I have read convincing arguments that, at least in the short term, it would make the atmosphere explosive.

Methane-air mixtures will not burn at all until they are at least 5% methane. Enough methane to constitute 5% of the mass of the atmosphere is...not going to happen. The concentration of methane in the air currently--which is too high, for global-warming purposes--is only 2 parts per million.

I know this, which is why I said "in the short term," though in retrospect I should have clarified. This danger is the greatest immediately after a release of significant amounts of methane, such as the huge amount of methane located off the coast of California. Before the methane is dispersed, it is an explosion waiting to happen.

if the ocean warms that much, we're pretty much screwed anyway.

That's the problem with a lot of these 'runaway feedback loop' scenarios, we'd already have to be eyebrow-deep into worst-possible-case territory for most of them.

According to this site, only a five-degree change in the temperature of the water around the deposits is necessary, assuming no pressure change either. However, you do not necessarily have to warm the whole ocean to this degree.

http://www.sciencedaily.com/releases/20 ... 080810.htm

Granted, I'm by no means saying this IS going to happen, only that it is a possibility, and one that would suck.

[EdgarJPublius]

'only' five degrees is extremely misleading, especially considering the deposits are generally in deeper, colder water that will be the least effected by climate change, and that such a change in average temperature would be accompanied by multi-meter water level rises and a die-off that would make the K-T extinction look like a mild flu season.

Virtually no one is predicting oceanic temperature change of even one degree in anything less than a hundred years, and more moderate predictions range from several hundred years to a thousand years.

The Clathrate 'gun' is nothing more than a fairy-tale, even a fraction of the climate change necessary to set off methane clathrate deposits would be an apocalyptic scenario even without these deposits being released into the atmosphere.

[roflwaffle]

Since when did the Clathrate gun idea get lumped into anthropogenic climate change? IIRC it was an attempt to explain the large increases in temperatures after ice ages millions(?) of years ago (Sea level drop is supposedly enough to decrease the pressure above enough clathrate deposits to warm the atmosphere back up), not speculation about some wild doomsday scenario.

[phonon266737]

You also need to think about these things in a physics sense. A solid in bulk form, but within a few degrees of it's melting temperature, is hardly stable. We can't ignore things like the Boltzmann distribution

At any given moment, there is a portion of the dissolved hydrates with significantly more energy than the bulk average. If these hydrates were a "gun" ready to go off with a few degrees more energy (a few more degrees moves the peak to the right of E_a),they would be like a simmering pot of water right now, and for the last X millions of years. If that was the case, they probably would not be there today.

Also, when I look up a phase diagram

MH stability curve.jpg (21.59 KiB) Viewed 3247 times

The phase change line is around 15 C for the deep stuff. Comparing the phase change line to the temperature gradient in the ocean, It seems to me that the only depth in which a few degrees could shift the hydrate into a different section, is ~ 500m or less. As you get to the deeper, high-pressure deposits that we're so worried about, the temperature change necessary becomes 10, 15 C.

I can't see how this is anything but a fairy tale. The shallow, low pressure deposits formed by decaying organic matter are simmering off into the seabed all the time - this is nothing new. But as for the deep deposits? You're talking about a climate shift where T_{sea floor} = T_room

[CorruptUser]

I'm not convinced that climate change will turn us into a giant desert; wouldn't warmer oceans mean more moisture in the atmosphere meaning much more rain, as well as counteracting (some) of the rising sea levels? That would mean many more parts of the world would resemble a swamp or jungle (wetland or rainforest, for the politcally correct); the Sahara desert actually becomes wetter when the temperature is higher.

Of course, this doesn't bode too well with biodiversity, as many species that exist in only one area will become extinct if their niche suddenly disappears.

Even if one pole completely melts in the summer, the other pole will still be in complete darkness at the same time, so the doomsday scenario of sea-levels rising 100 feet seem a little far-fetched.

The problem I see is the adjustment period; once-ideal farmland might become unproductive before now-ideal farmland is developed. Imagine if India or China lose even 1/5 of their food production; unless they lose 1/5 of their population as well, or are capable of surviving on rations, expect invasions of neighbors with farmland or mass starvation. I think the main problem is we don't know for sure what will happen, so there really is no way to plan for any outcome, short of planning for every single scenario (only to be hit by a scenario you didn't forsee).

Regardless of the outcome, non-carbon energy sources are still a good idea, if only because we are running out...

[Azrael001]

The sea level doesn't need to rise 100m to become a massive problem. I could explain everything here, or I could post a report that I did for my Climate change class, and cover some other stuff that people have briefly skirted earlier in the discussion.

You can read it all here under the spoilers. (It's about a page and a half minus sources)

Spoiler:

An important implication of climate change is the potential for rapid sea-level change. With recent warming trends, the change will almost certainly be a rise. There are two main mechanisms for sea level change: mass change or density change. Mass change is a result of altered levels of water availability. The primary source of water that adds to current sea-level rise is land-ice melt². Accelerated levels of glacial melt will increase the rate of sea-level change. The second source of sea-level change is more directly linked to temperature. As air temperatures increase, so too will sea surface temperatures. Thermal expansion accounts for approximately 90% of the density change and freshening (lowering salt concentration) accounts for the other 10%².

There are two main sources of land ice: the Greenland ice sheet and the Antarctic ice sheet. Combined they contain enough ice to raise sea levels by about 64m if they melt completely². Currently melt from these ice sheets and smaller glaciers contribute about 1.2mm² rise per year, but this is expected to accelerate as positive feedback effects alter the way in which the local climate behaves. The Greenland ice sheet has recently been contributing 0.75mm per year to sea-level rise, but it's rate of melting has been accelerating at an alarming rate⁵. The West Antarctic ice sheet is also experiencing accelerated melt rates. The East Antarctic however is growing by 45 billion tonnes per year, which is equivalent to slowing sea-level rise by 0.12mm per year⁶. Increased precipitation on the ice sheet is the suspected cause of the growth, and it is expected that precipitation will increase over the East Antarctic ice sheet as atmospheric temperature continues to rise⁶.

The temperature of the ocean varies based on both depth and latitude, as does salinity. Additionally, the amount that water expands when heated (or contracts when cooled) increases at higher temperatures. This means that thermal expansion will have a greater effect on sea level closer to the equator where water is warmer. Expansion due to lowered salt levels will be more pronounced closer to the major fresh water inputs, the ice caps at the poles. Initial changes will be on the surface, as deep water mixing occurs only in two main locations, one in the North Atlantic, and the other in the South Pacific.

The instrumental record of sea level reaches back to the 1870s, but is less accurate than the satellite records that we use today. Measurements from before the 1990's are based on tidal gauges, which lack the precision of the satellite measurements, both because the measuring stations are only on land, and thus lack mid-ocean data, and because the tidal measurements are based on sea-level relative to land which is not constant. The positions of the measuring satellites however are precisely tracked, and their orbits monitored². The figure below shows both the available data on sea level and the projected sea level change both before and after the instrumental record. The width of the band indicates level of certainty, thin being high certainty and thick being low.





Of concern: The direct effect of sea-level rise is clear: higher water levels will inundate low lying land. This can be mitigated at great cost by creating structures to hold back the water. The Netherlands provide the best example of a country already at great risk of flooding. The projected extra annual cost for the Netherlands to sustain their current infrastructure, and protect against further rise is $2.2 billion⁷. Most countries have not got the infrastructure in place to protect themselves. Bangladesh for example could face losing up to 15% of it's land area by the year 2100⁸. As sea-levels increase coastal land will become less useful even before they are inundated. Again in Bangladesh it is expected that increased soil salinity could reduce crop output significantly⁸. About 10% of the world's population live in low elevation zones (10m or less above sea-level) slightly over half of these people are concentrated in urban areas⁴.

While the direct effects of sea level change will not affect Canada (The basis of the report was to write a letter to a hypothetical politician providing an explanation that a layman could understand) as much as many countries, the indirect effects: massive amounts of environmental refugees and reduced food availability, will tax our own resources, and damage our economy. More importantly, global resource strain, and mass movements are very likely to cause political instability, and it is possible that Canada, being a rich country, both in resources and material wealth, could be resented for it's comparative lack of problems.


Uncertainties: There are few uncertainties remaining regarding sea level change. As technology has improved, so too has our ability to accurately measure the relative level of the ocean. In both the 42 and 10 year calculations there has been an under prediction of sea-level rise, though the difference between calculated and observed has narrowed considerably since the advent of the information age.

Ocean currents are controlled by both variations in temperature and salinity. The alteration of the temperature and salinity gradients the Atlantic Meridional Overturning Circulation (MOC) could decrease as a result of both warming and increased desalinization². As the MOC is strongly related to local climate, this could result in drastic changes to the local climate².

My opinion: It seems pretty clear that ocean levels are continuing to rise. Highly accurate satellite observation over closely matches ground based measurements. The continuing rise is clear,as is the acceleration of that rise. Satellite monitoring of the oceans should continue, as future policy decisions should be made based on what is happening, rather than past projections of future events. More research should be placed in holding flood waters at bay at a relatively low cost, as there are many vulnerable cities which need to be protected, and many of these are in fairly poor countries. The MOC should also continue to be monitored as our current data resolution is too low to make any decent predictions about it's potential changes in behaviour with respect to temperature and salinity².

Citations

Spoiler:

1. IPCC 2007 - Chapter 4

Lemke, P., J. Ren, R.B. Alley, I. Allison, J. Carrasco, G. Flato, Y. Fujii, G. Kaser, P. Mote, R.H. Thomas and T. Zhang, 2007: Observations: Changes in Snow, Ice and Frozen Ground. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-6.html#4-6-1

2. IPCC 2007 - Chapter 5

Bindoff, N.L., J. Willebrand, V. Artale, A, Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and A. Unnikrishnan, 2007: Observations: Oceanic Climate Change and Sea Level. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-5.html
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-6.html

3. IPCC 2007 - Chapter 10

Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver and Z.-C. Zhao, 2007: Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10s10-6-2.html
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10s10-6-5.html

4. Low Coastal Zone Settlements. McGranahan, Gordon. Balk, Deborah. Anderson, Bridget. Tiempo Issue 59 April 2006 pg 23-26

5. Partitioning Recent Greenland Mass Loss. van den Broeke, Michiel. Bamber, Jonathan. Ettema, Janneke. Rignot, Eric. Schrama, Ernst. Jan van de Berg, Willem. van Meijgaard, Erik. Velicogna, Isabella. Wouters, Bert. Science 13 November 2009: Vol. 326. no. 5955, pp. 984 - 986 DOI: 10.1126/science.1178176 http://www.sciencemag.org/cgi/content/full/326/5955/984#F2

6. Snowfall-Driven Growth in East Antarctic Ice Sheet Mitigates Recent Sea-Level Rise
Curt H. Davis, Yonghong Li, Joseph R. McConnell, Markus M. Frey, Edward Hanna. Science Express May 2005
http://www.sciencemag.org/cgi/reprint/sci;1110662v1.pdf

7. Working together with water: A living land builds for its future Findings of the Deltacommissie 2008. Secretariat Delta Committee. Hollandia Printing.

8. Sea Level Rise, A Threat to the Coast of Bangladesh. GOLAM MAHABUB SARWAR, MAMUNUL H. KHAN. Internationales Asienforum, Vol. 38 (2007), No. 3–4, pp. 375–397

[Inglonias]

My personal view on climate change can vary from "oh god, oh god, we're all going to die" to "this is going to go away when clean energy takes off" and currently its closer to the former.

I haven't really heard much about climate change in the news lately. I keep an RSS feed about it, though, and recently (just today) a story in the Washington Post has shaken me up a bit. I realize what it was in the article that panicked me:

How will we feed ourselves adequately if our breadbasket is a desert? Answer: We won't, and there will be social unrest as a result. How much is anyone's guess, but people don't sit still when food gets scarce. Indeed, when the options are extreme hunger or pillaging the neighboring village, history tends to favor pillaging.

I wonder how climate change will or won't affect food production? Is this guy right? I'm not sure.

NOTE: I am not certain completely of the bumping rules in Serious Business, but my current understanding is that its better to necro than create a duplicate thread.

[Pez Dispens3r]

I wonder how climate change will or won't affect food production? Is this guy right? I'm not sure.

During the ice ages most of the world was dessert because of desiccation: as a freezer dries out mince, the larger ice caps sucked all the moisture from the air and there was much less rainfall all over the globe. With global warming there will be quite a lot more rainfall and carbon-dioxide which will boost crop growth in the long term. However, global warming also presents two major problems for food production. Firstly, more moisture in the atmosphere will mean the tropical climates will extend their reach well beyond that of Cancer and Capricorn, and suddenly land that was prime for wheat production will be completely useless for it. Secondly, precipitation patterns will change: there will be more rain, but in some areas which now enjoy steady rain throughout the year it will soon be intermittent or non-existent. That is, some deserts will become bread bowls as traditional bread bowls cease to exist. Farmers will also have to contend with such events as a fluctuating El Niño-La Niña pattern.

The upshot? Maybe a billion lives lost.

Note that this would not necessarily be because of starvation. In famines, people don't tend to die from lack of food. What they die from is movement and disease: there's no food locally, so you move somewhere else and die on the road from exposure. If you have food, then people migrate from all over and they're all bringing different diseases. Further, in developing countries that still rely on wells for water, if there's no rain the well-levels get low and stagnate, and water-borne diseases thrive. These were the mechanisms that accounted for most of the fatalities in the Darfur famine, rather than from a lack of nutrition (although, of course, malnutrition makes you more susceptible to disease, it was very rare to find someone who had died just from malnutrition).

None of this should be too problematic for the developed world, however. They can always use their resources to entice farmers to adopt crops which do better in a sub-tropical or tropical climate, and they can more easily locate emerging bread baskets. It will come at a high economic cost but at a low cost of life.

NOTE: I am not certain completely of the bumping rules in Serious Business, but my current understanding is that its better to necro than create a duplicate thread.

Azrael is a fickle moderator, likely to ban you as soon as look at you. The best tactic is to do whatever you want and placate him with scotch.

[Trasvi]

In Australia there is massive debate at the moment over the governments plan to introduce a 'carbon tax' (which will eventually change into an emission's trading scheme) to reduce our CO2 emissions and thus reduce global warming.

What do you think about global warming? Is it real or imagined? Is it human caused, a natural phenomenon, a little bit of both or a lot of nothing?
If it is real, how and why (or why shouldn't) we be combating it?

There seems to be a lot of misinformation circulating. In the words of a (discredited) climate change sceptic: "If you pick your start and end points well, you can prove anything you want" (he then proceeds to pick a start and end point...). Depending on who you listen to, the world is in the start/end/middle of a warming/cooling period and is warmer/cooler than it should be given the data. This trend is caused by humans/volcanos/clouds/the sun/flying spaghetti monster and will lead to armageddon/floods/ice age/prosperity. Most governments don't seem to want to do anything because its a) not real, b) not human caused, c) not their problem, d) too expensive, e) too complicated, f) not going to change anything unless country X (usually China) also changes.

So, what does this board of scientists and mathematicians believe about global warming, climate change, and ways to combat it?

[++$_]

Keep in mind that not everyone here is a scientist or a mathematician.

Obviously global warming is real. There are two categories of objections to the idea: serious objections and stupid objections.

Serious objections come from people who aren't convinced by the science because the climate is an extremely complex system that's very hard to predict. These basically boil down to saying "We don't know for sure that we aren't missing something," which is true, but also not really relevant, because we never know for sure that we aren't missing something.

Stupid objections come from people who don't understand the science. These are things like "How can a cool atmosphere heat up the planet which is warmer than it", "But the climate is colder than it was 65 million years ago", "Carbon dioxide is essential for life", "The major contributor to the greenhouse effect is water vapor so carbon dioxide can't make a difference", and so on. I'm sure I'm missing some.


As for doing something about it, that is a much trickier question, because it's a question of economics. Personally, I think a carbon tax is a great solution because it is the perfect solution economically -- the externality is internalized, and that's that.

People who object to carbon regulation on economic grounds usually base their objection on the idea that reducing carbon emissions will hurt the economy. That position only makes sense if you disregard the harm that the emissions themselves do. I have no idea how big the externality caused by every ton of CO₂ actually is, but I believe it's possible to figure that out. If so, implementing a tax in that amount would benefit the economy, not hurt it.

[SlyReaper]

Keep in mind that not everyone here is a scientist or a mathematician.

Obviously global warming is real. There are two categories of objections to the idea: serious objections and stupid objections.

Serious objections come from people who aren't convinced by the science because the climate is an extremely complex system that's very hard to predict. These basically boil down to saying "We don't know for sure that we aren't missing something," which is true, but also not really relevant, because we never know for sure that we aren't missing something.

I think it is relevant. The main question behind climate change isn't "is it actually happening", but "are humans causing it". Or more accurately, "how much of this climate change is caused by us, and how much is caused by natural processes we have no control over?". Because if the answer to that question is that it's 99.999% natural processes, then cutting back our carbon emissions at the expense of industry will ultimately be an exercise in futility; the Earth would continue heating up regardless.

However, until we know the answer to that question, it's a good idea to do what we can to change our behaviour just in case most climate change is anthropogenic. The cost of having the Earth heat up beyond our capability to deal with it far outweighs the short-term cost of cutting our carbon emissions.

[++$_]

I don't think you understood what I was saying. I was saying that pointing out "All of this could be wrong if we have missed something important" is not really relevant. ANYTHING could be wrong if we have missed something important. We have to assume that we didn't miss something important, because a lot of very smart people and an even larger number of less smart people have thought about it and no one has managed to come up with the thing we're possibly missing.

But, if we do discover that we missed something important, then of course it's time to rethink things.

[jakovasaur]

I don't think you understood what I was saying. I was saying that pointing out "All of this could be wrong if we have missed something important" is not really relevant. ANYTHING could be wrong if we have missed something important. We have to assume that we didn't miss something important, because a lot of very smart people and an even larger number of less smart people have thought about it and no one has managed to come up with the thing we're possibly missing.

Of course it's not helpful to say "well, we could be wrong", but it is equally unhelpful to say "well, this is our best guess, so we have to assume we didn't miss anything important." In other words, it isn't irrelevant to consider our degree of (un)certainty, because that has a direct bearing on the cost-benefit analyses we need to run in order to decide what to do.

[Charlie!]

Obviously global warming is real. There are two categories of objections to the idea: serious objections and stupid objections.

Serious objections come from people who aren't convinced by the science because the climate is an extremely complex system that's very hard to predict. These basically boil down to saying "We don't know for sure that we aren't missing something," which is true, but also not really relevant, because we never know for sure that we aren't missing something.

I think it is relevant. The main question behind climate change isn't "is it actually happening", but "are humans causing it". Or more accurately, "how much of this climate change is caused by us, and how much is caused by natural processes we have no control over?". Because if the answer to that question is that it's 99.999% natural processes, then cutting back our carbon emissions at the expense of industry will ultimately be an exercise in futility; the Earth would continue heating up regardless.

However, until we know the answer to that question, it's a good idea to do what we can to change our behaviour just in case most climate change is anthropogenic. The cost of having the Earth heat up beyond our capability to deal with it far outweighs the short-term cost of cutting our carbon emissions.

I think you're misunderstanding ++$. He didn't say "we don't have any answers," he said "because we can only have finite evidence, the answers we have are fallible."

So we can answer your question. Humans are having a big enough impact on climate that it's worth it to stop. Since this is a human answer and not a magical divine answer, we might find out tomorrow that it was aliens playing a prank, and scientists everywhere would look silly. But all we've ever got are human answers.

[Plasma Man]

In some ways, belief in anthropogenic climate change isn't a necessary prerequisite to support a carbon tax. I do think that human activity is warming the climate, and large studies such as those undertaken by the Intergovernmental Panel on Climate Change have reported that the planet is definitely warming, and there's a greater than 90% probability this is because of human activity. So why do I say that it's irrelevant for this? Because pretty much everyone admits that there are finite amounts of fossil fuels available. A carbon tax makes using fossil fuels more expensive and will give a push to help find alternatives, which we're going to need sooner or later.

[Trasvi]

I completely agree with that sentiment plasma man. A carbon tax should be supported if for no other reason than to reduce our reliance on fossil fuels.

However, one of the main lines our opposition is pushing is that a carbon tax (or emissions trading scheme) will make Australia uncompetitive against our major trade partners (China, Japan, India, USA) who don't have a carbon tax of any sort.

One issue personally have with the science of climate change is the incredibly short time spans that people are talking about. 10 years, 150 years, even 1 million years is pretty minuscule in the 4 billion year history of the Earth; and the further back in time we go, the less actual knowledge we have. With all the talk of cyclical trends (sun irradiance on a 11/200 year cycle, el nino on 5 year) and feedback loops etc, how do we know that we're not just in a cyclic up/down trend? Are we heading towards a maximal or a maximum point in the cycle? And if it truly is cyclic, or if the sun truly is just getting warmer and warmer, aren't we eventually doomed anyway?

[Hawknc]

Well, let's not pick and choose our timescales here. If you're concerned about cycles with million-year periods, then we would barely be able to perceive it across the entirety of human civilisation. The reality is that we can see a definite warming over the last hundred years or so which can't be completely attributed to any natural variability that we've seen. So while we could be experiencing a completely natural uptick and there's a corresponding downtick just around the corner, there's no evidence to suggest that's the case. We could just as well suggest the warming is due to aliens lighting invisible farts directed at us.

Edit: oh right, I was going to say something about the carbon tax too. The argument that the carbon pricing system will affect our competitiveness might hold water if we weren't giving extremely generous subsidies to trade-exposed industries. And households, who aren't even paying for CO2 emissions. IMO, too much of the money is going back to the polluters, disincentivising any real investment in lowering their emissions, but I understand that there's a need for political compromise to get anything done.

[Iceman]

We have absolutely not metrics to tell us if the recent changes are normal or not though.
We quite literally have no idea what short term cycles have occurred in the past, nor why they were caused...we only know that the completely natural non-human affected temperature shifts the Earth is capable of are magnitudes higher than the one we are seeing now.

So if we see a temperature variance in the past century that we cannot reliably attribute to anything in addition to us not knowing if that temperature fluctuation is rare or happens frequently...I can't see why we would decide to take an arbitrary action with the goal of 'reversing' it for no apparent reason.

The whole reason they changed the name to 'Climate Change' is so that it could never be disproven no matter what happens. And how all pollution ended up being 'Carbon' I have no idea.

I remember when crops were all about to die because the world was cooling, and I remember when Acid Rain was going to kill me and everyone I know, and when the Ozone layer was going to be gone forever.

Ya...we shouldn't pollute stuff for no good reason...BUT we do not need a 'Golly Gosh Darn Gee Wiz WE"RE ALL GONNA DIE TOMORROW!' pretend boogey man thing to do it. It's just a big scare thing to get us to do stuff we logically should be doing anyway....

We should get off fossil fuels because it's inefficient and Nuclear is better...we should be dumping less chemicals 'cause it kills things and ruins areas we need...We should recycle metals because there's a finite amount of metal...
All of these things should be done for valid economic reasons...not scare tactic illogical ones about water levels rising about a point that is physically possible given the amount of water on Earth.

[Hawknc]

We quite literally have no idea what short term cycles have occurred in the past, nor why they were caused...we only know that the completely natural non-human affected temperature shifts the Earth is capable of are magnitudes higher than the one we are seeing now.

How short term are we talking, here? We have over a century of pretty accurate data to help us see any cycles on that timescale. On a thousand-year timescale, we have an understanding of historical temperatures and the accuracy to which we can estimate them. Even moving to paleoclimate research, we need to take indirect measusrements, but the accuracy of them is fairly well established and the methods are understood. So we do have some understanding of the natural cycles at work, but none of them fully explain the rising temperature trend we've seen since the Industrial Revolution:

Spoiler:

But we do know that greenhouse gases like carbon dioxide and methane have been steadily increasing over the same period:

Spoiler:

And we know the relationship between greenhouse gases and temperature, which has been recognised for over a century. Occam's Razor suggests that the thing we know affects temperature, and has been increasing, is likely at least partially responsible for the increase in temperature.

[nitePhyyre]

Serious objections come from people who aren't convinced by the science because the climate is an extremely complex system that's very hard to predict. These basically boil down to saying "We don't know for sure that we aren't missing something," which is true, but also not really relevant, because we never know for sure that we aren't missing something.

That's a serious objection?

I think a better objection is the idea that geo-engineering the planet cooler is cheaper than reducing the use of carbon. I don't know if it's true or not, but it still seems somewhat serious.

[Iceman]

We quite literally have no idea what short term cycles have occurred in the past, nor why they were caused...we only know that the completely natural non-human affected temperature shifts the Earth is capable of are magnitudes higher than the one we are seeing now.

How short term are we talking, here? We have over a century of pretty accurate data to help us see any cycles on that timescale. On a thousand-year timescale, we have an understanding of historical temperatures and the accuracy to which we can estimate them. Even moving to paleoclimate research, we need to take indirect measusrements, but the accuracy of them is fairly well established and the methods are understood. So we do have some understanding of the natural cycles at work, but none of them fully explain the rising temperature trend we've seen since the Industrial Revolution:

Spoiler:

But we do know that greenhouse gases like carbon dioxide and methane have been steadily increasing over the same period:

Spoiler:

And we know the relationship between greenhouse gases and temperature, which has been recognised for over a century. Occam's Razor suggests that the thing we know affects temperature, and has been increasing, is likely at least partially responsible for the increase in temperature.

I mean we don't have data on Time frames of say, 100 years...500,000 years ago.
In other words, there may have been a period between 76,300 BCE and 76,200 BCE that looks identical to the past 100 years, and we have no way of knowing that.

We also do not in fact know what truly raises temperture, we are only assuming a cause and affect based on very recent history. We see that CO2 and temperature are moving in the same direction...but it's also possible that higher temperatures cause more CO2 and Methane. (Melting releases trapped gases, evaporation encourages a heavier atmosphere and oceans absorb less CO2, more heat aids life and causes more emissions, heats causes more wildfires, internal heat causes more eruptions etc... etc...)

Occam's Razor in reality suggests that an increase in heat...is most likely due to small changes in the Huge Ball of Fire that provides all our heat, or due to changes in climate which we already know naturally varies from 'Complete Global Freeze' to 'Ball of Molten Lava'

The simple fact of it is, these temperature rises and drops have occurred before, and will continue to occur. We know for a fact they Have occurred...we do not in any way know the SPEED in which they occurred with any accuracy. We merely are looking at the past couple hundred years, and then comparing it to now and saying 'Hrm, that seems weird'

We have no idea how sunspots affect our temperature, we don't know how ultraviolet radiation affects the atmosphere, we don't know how electromagnetics affect our own core, we don't even know what is at the bottom of the ocean releasing what heat and gas, we don't even agree on what 'Global Temperature' means...since surface temperature can rise while Ocean and atmospheric temperature drops. We don't know how weather patterns affect overall temperature, or how overall temperature affects weather patterns. We don't know how biological life changes globally if the temperature rises or drops a degree.

And perhaps most of all, we have no idea why Co2 rises or drops naturally in the first place. How has CO2 in the past been higher than it is now before it could have been us?...and perhaps more importantly, how did it then get down to low levels afterwards?

Humans like to assign a reason to things...and we like it even more when the reason is something we did or something we can 'fix'
But that's really all this is.

We can say 'Oh look it rose really fast since industrialization...' But it's risen like 0.8 degrees since 1900.

It rose 0.8 degrees from 800AD to 900AD. It dropped 0.7 degrees during the 'little ice age' from 1500 to 1600.

Total variance in the past 2000 years was about 1.6 degrees up and down....
Total variance in the past 500,000 years is about 10 degrees

I just don't think we have anything at all that really points to this being unusual, this could happen all the time and we have no way of knowing.





It's just alarmist guesswork.

[Hawknc]

We also do not in fact know what truly raises temperture, we are only assuming a cause and affect based on very recent history. We see that CO2 and temperature are moving in the same direction...but it's also possible that higher temperatures cause more CO2 and Methane. (Melting releases trapped gases, evaporation encourages a heavier atmosphere and oceans absorb less CO2, more heat aids life and causes more emissions, heats causes more wildfires, internal heat causes more eruptions etc... etc...)

Both are true. It's called a "positive feedback loop" and it is responsible for most of the alarming predictions you're concerned with. Higher CO2 causes higher temperatures, which causes higher CO2, etc...there is a concern that we could reach a point where even if we stopped emitting everything, the global mean temperature continues to increase and eventually stabilise at a far higher level than we would have seen without anthropogenic forcing. But I think you missed my point: we know CO2 traps heat because we have done it countless times in a laboratory. It is experimentally confirmed to cause warming. That, I think, seems far more likely than a hundred-year blip that occurs every few thousand years that has never, ever been suggested by any record.

The huge ball of fire (I'm going to call it that from now on, because that term is kind of awesome) definitely has an impact on global climate. I doubt you'll find any credible climate scientist who would claim otherwise. For instance, there is a recorded minimum in solar activity (known as the Maunder Minimum) that corresponded closely with the Little Ice Age, and sunspot activity has increased since then...until the 1950s, when recorded activity peaked and has since stabilised. The global mean temperature, on the other hand, continued to rise. Recently the sun has actually gone into a quiet period, which we discussed in N&A, and I'm going to shamelessly re-use a graph I posted in that thread to highlight what we would expect to see if the HBOF (and other natural sources, like volcano activity) was the primary factor in the temperature delta we're seeing:

Spoiler:

(That graph does, incidentally, provide a great comparison between land and ocean temperatures. Spoiler alert: they're both going up.)

Your questions deserve more detail than I can go into right now, unfortunately, but hopefully someone else can step in and correct me if I'm going down the wrong path here.

[Iceman]

Both are true. It's called a "positive feedback loop" and it is responsible for most of the alarming predictions you're concerned with. Higher CO2 causes higher temperatures, which causes higher CO2, etc...there is a concern that we could reach a point where even if we stopped emitting everything, the global mean temperature continues to increase and eventually stabilise at a far higher level than we would have seen without anthropogenic forcing. But I think you missed my point: we know CO2 traps heat because we have done it countless times in a laboratory. It is experimentally confirmed to cause warming.
That, I think, seems far more likely than a hundred-year blip that occurs every few thousand years that has never, ever been suggested by any record.

Well, there clearly Is no positive feedback loop in nature, since CO2 level have been higher and dropped and higher and dropped....there's some mechanism which causes them to drop.

Yes, we do know Co2 can trap heat...we do not, however, know the Earth's ecological reaction to to high levels of Co2.

Again, Hundred year blips have occurred 3 times in just the past 2000 years...and beyond that we haven't a single goddamn clue whether they've happened or not because we have no way to see such small time intervals on a timescale of like 500,000 years.
So it's not that it's "Never been suggested by any record" it's that "It cannot possibly even begin to be commented on by any record" beyond human history.

It's not that we have this record and we can't see this occurring before.....we simply have no record of it because we lack that level of accuracy. We're trying to extrapolate what the earth's temperature was 3 million years ago based on a core sample in Antarctica and then guess what it was like at that time in Madrid. It's remarkable they can do it at all...but comparing that to actual measured temperatures today just isn't possible.

Even with the Sun thing...we didn't know sun spots were a cycle until a few decades ago...we didn't know the sun ejected mass on a daily basis until 1995...we didn't know about a lot of its electromagnetic interaction with earth until the 2000s...
I've gone through a list there before of a bunch of stuff we have no idea about.
With uncertainty about what causes gases to accumulate or dissipate in the atmosphere...
without certainty on how the ecology of the planet adapts to imbalances
without knowing how the Earth actually responds to Solar changes
without knowing past behaviour of the Earth's temperature on this scale in pre-human time
without knowing what is even in 90% of the ocean
without even knowing if its going to rain in Chicago tomorrow

and perhaps the most important one to me.....Without in any way having any reason to believe that the current temperature is the Optimal temperature of Earth...

We're deciding that we're the cause.

Or we could just admit we actually don't know...but that's not too politically popular, and it doesn't sell many green-friendly products to Liberal Arts students

[elasto]

Well, there clearly Is no positive feedback loop in nature, since CO2 level have been higher and dropped and higher and dropped....there's some mechanism which causes them to drop.

This is expressing it far too strongly. There are, of course, numerous positive and negative feedback loops; Some of the geoengineering solutions target boosting the negative feedback ones. All we can safely say is that the positive feedback loops have never dominated in earth's history to date, but there could easily be a tipping point at which they do.

I've gone through a list there before of a bunch of stuff we have no idea about.
With uncertainty about what causes gases to accumulate or dissipate in the atmosphere...
without certainty on how the ecology of the planet adapts to imbalances
without knowing how the Earth actually responds to Solar changes
without knowing past behaviour of the Earth's temperature on this scale in pre-human time
without knowing what is even in 90% of the ocean
without even knowing if its going to rain in Chicago tomorrow

and perhaps the most important one to me.....Without in any way having any reason to believe that the current temperature is the Optimal temperature of Earth...

We're deciding that we're the cause.

All of this is largely missing the point for me. But let's break it down a little:

Firstly, there is no doubt at all scientifically that the global temperature is rising. There is some doubt scientifically that it is wholly caused by human activity, but that doubt is very small at present.

I will agree that there is no real reason to assume the current global temperature is optimal - and global cooling is certainly a more dangerous prospect overall than global warming. Indeed, overall, for life collectively, almost certainly a higher temperature will suit just fine (so long as it vaguely stabilizes). However, the problem is the sheer speed at which global warming is occurring. Think of the social tensions currently being caused by a million Mexicans coming into the US illegally, or the tensions seemingly resulting when Brown people currently go anywhere in any great numbers. And then understand that, at projected rates of warming, enormous numbers of people are going to be displaced by countries entering permanent famine or becoming partly or totally submerged underwater. Are you happy to play your part receiving in or otherwise permanently taking care of some of these hundreds of millions to billions of affected people? Moreover, though it surely wont occur between the major powers, wars over precious resources, including fresh water, are surely going to be on the increase. Perhaps there will be a whole new motivation and justification for terrorism if it is perceived that Western countries look on idly by while their emissions make them rich but destroy the environment of various already poor countries. And all of that is not to mention the fact that there are going to be a lot more extreme weather events such as hurricanes/tornadoes at home costing us all more money to clean up.

And, so, in the end, it's somewhat like the choice to pay insurance: If the event you are insuring against never happens, it can feel like wasted money, but it wasn't really. If we adjust to a low-carbon economy quicker than we otherwise might, and anthropogenic global warming is not actually occurring, well, we can feel like it's wasted money. But the best scientific evidence we have is that is that it is real, and that preventative measures will be vastly cheaper than doing nothing.

Personally I'd like to see geoengineering solutions mooted more seriously, as I think they could be very cheap and very effective, but I acknowledge there are numerous complications and considerations for going down that path - not least the fact that if they do work, in a world where there is battle for control of the thermostat in every office and home - what is the battle over the world's thermostat going to be like :p

[Iceman]

Firstly, there is no doubt at all scientifically that the global temperature is rising. There is some doubt scientifically that it is wholly caused by human activity, but that doubt is very small at present.

For me it is really down to this.

The doubts over whether humans are causing this are so huge that it's hard to discuss it much further.

There is simply no evidence that it's us...there's no evidence that the speed in unusual in any way. NONE at all. We are simply assuming, based on nothing that its too fast.

We have absolutely no basis for comparison at all.

If we actually take directed actions design to cool the Earth intentionally, and it turns out we were already about to cool off...we're just hurting ourselves. It's not a 'Oh well, we tried and it didn't matter' scenario. It does matter is we spend Billions fixing a problem that isn't even real.

I'm sorry, but this is really a Y2K, 2012, Acid Rain, Global Cooling-like completely fake problem. It's not real....it's just Incredibly valuable to everyone to pretend it is.

[Kulantan]

I'm sorry, but this is really a Y2K, 2012, Acid Rain, Global Cooling-like completely fake problem. It's not real....it's just Incredibly valuable to everyone to pretend it is.

Huh? Was there some kind of "acid rain will melt the whole planet" type thing? Because acid rain is an actual thing that does cause non-world-ending type problems.

[Hawknc]

If we actually take directed actions design to cool the Earth intentionally, and it turns out we were already about to cool off...we're just hurting ourselves. It's not a 'Oh well, we tried and it didn't matter' scenario. It does matter is we spend Billions fixing a problem that isn't even real.

Geoengineering aside, cooling the planet is no longer an option. We're past that point. All we're trying to do now is slow the rise to what we would see under purely natural forcing - mitigation and adaptation are the buzzwords these days, rather than prevention.

Well, there clearly Is no positive feedback loop in nature, since CO2 level have been higher and dropped and higher and dropped....there's some mechanism which causes them to drop.

This is expressing it far too strongly. There are, of course, numerous positive and negative feedback loops; Some of the geoengineering solutions target boosting the negative feedback ones. All we can safely say is that the positive feedback loops have never dominated in earth's history to date, but there could easily be a tipping point at which they do.

Yeah, I think there is a misunderstanding of what a positive feedback loop entails. Positive feedback is when you push on a system in a certain direction, and there are mechanisms in the system that amplitude the effect of that push. Likewise, a negative feedback loop would act opposite to the forcing, muting its effects. It's not a permanent state; in the case of climate science, a positive feedback loop might disappear when a state changes (e.g. if warming is causing causing reduced albedo due to less arctic ice which in turn causes increased warming, that feedback loop will stop when the ice reaches a stable amount, even if that amount is zero). The concern with global warming is not that we'll experience a Venus-style catastrophic event where temperatures just keep rising indefinitely, but that the global mean temperature will stabilise at a level which is much less beneficial to us than the current one.

[Zamfir]

The doubts over whether humans are causing this are so huge that it's hard to discuss it much further.

There is simply no evidence that it's us...there's no evidence that the speed in unusual in any way. NONE at all. We are simply assuming, based on nothing that its too fast.

Can you give an impression of what you would consider good enough evidence, or where you think the problems mostly lie in the current evidence?

I'd say there are a number of things basically beyond controverse. Perhaps those are together not enough to make a completely closed case, but they are in my opinion strong enough that you have to show an alternative case to cast doubt. It is no longer enough to just poke at the weaknesses of the standing case.

Things that I'd say are pretty much established:

- Global average temperature has risen over the last the century, and is still rising. This is a trickier claim than it looks. "Global average temperature" is not a directly measurable thing, it's a constructed aggregate with lots of potential pitfalls. And "rising" too is only a trend in a far more complicated time series. But over the last 20 to 30 years, we have learned enough to make this claim with high certainty anyway.

- Greenhouse gases exist, and are present in our atmosphere. That is, there are gases that are observed to cause heat trapping under laboratory conditions.

- The presence of these gases has indeed a significant impact on the temperatures on the surface of the planet. This is a harder claim than the previous, since there is no direct counterfactual to compare it with in a laboratory. But any attempt to model temepratures on earth, from simple and rough to complicated, leads to far too low temperatures if they do not take greenhouse effects into account. And we have other planets and moons to verify such modelling attempts with. But simple models are not accurate enough to say something about the effects of changes in the greenhouse gas levels.

- Concentrations of several greenhouse gases are rising, in particular CO2. We can accurately measure their concentration in several ways, such as direct air samples or by observations of the optic properties of a column of the the atmosphere. This is a complicated technical issue, but pretty uncontroversial in its execution.

- The increase in greenhouse gases is caused by human activities. That's what our (imperfect) understanding of their spread and accumulation predicts, but it is also verified by isotopic measurements. The ratio of carbon-12 to carbon-13 in the atmosphere changes the way you would expect, if carbon levels are increasing as the result of fossil fuel burning.

- The observed increases in concentration, combined with the laboratory properties, are more than enough to explain the observed temperature rise in a naive simple model without much feedback mechanisms. This is called "forcing" and is the input for more realistic models.

The capstone of the evidence, which is perhaps more controversial, would be our detailed understaning and modelling of the relevant feedback mechanisms. The big weaknesses here are mostly forward-looking, in predicting which mechanisms will be relavant in the future, beyond the observed and studied range of parameters. But I'd say it is indeed reasonable to have doubts about the accuracy of our current understanding, even backwards-looking to already observed phenomena. This understanding is not as 'hard' as all the stuff above, even if it is the best we have. It is about combining imperfectly understood phenomena in complicated relations, which does have lots of room for error.

Still, that doesn't somehow make all the other stuff "just assuming". If you want to doubt the causal link between human activity to the observed tmeperature increases, you have to assume both that
A. Our detailed understanding of feedback mechanisms is completely wrong, in such a way that the (observed!) increased forcing from greenhouse effects is nearly fully counteracted by those feedback mechanisms,
and B. There are also other, as yet unobserved and unknown mechanisms that do produce the observed temperature increase, but that escape from those feedback mechanisms that negate the effects from greenhouse gases.

I'd say that either A or B separately would be a plausible doubt. But both at the same time is asking a lot. At the very least, people would have to describe the alternative mechanisms, and show their active presence at the same level of detail that the greenhouse gas mechanism has been observed. And yes, people have studied sunspots.

[elasto]

I too am confused about where all this doubt is. It's like when people doubt evolution: Sure, there could be something else at work that everyone's missed but the weight of scientific evidence at this point is definitely not suggestive of that.

Let's break it down into three parts:

(1) There is no doubt at all that the global temperature has gone up since industrialisation

(2) There is a very small amount of doubt that human CO2 emissions is the main culprit - although that isn't relevant to the need to do something about the rise in temperature: the massive economic damage caused by a rapid rise in sea level will happen regardless of whether the causative agent is industrialisation or not; It only has a bearing on what the solution would be - and even then lowering CO2 is still helpful because there is no doubt scientifically that lower CO2 = lower temperatures. All it really means if man isn't the primary agent is that a geoengineering solution is the only real option.

(3) There is a great deal of doubt as to what will happen next - but let's be clear about what we mean by that: the low end, most optimistic forecast is a 2C rise; Scientists agree that level of rise is now unavoidable due to past missed targets. The high end, pessimistic forecast is 8C+. 2 degrees is already enough to be mighty expensive economically, globally.

-------------------

The doubt, such that it exists, is akin to knowing that a hurricane has formed off the coast and is heading directly inland - and it may hit us with full force or it may yet veer off slightly with some of the damage mitigated. Thinking it might turn around 180 degrees and miss us completely is just blind hope, though, and that is no way to approach such a serious issue - even though there is a tiny outside chance that might indeed happen.

[Dark567]

Edit: oh right, I was going to say something about the carbon tax too. The argument that the carbon pricing system will affect our competitiveness might hold water if we weren't giving extremely generous subsidies to trade-exposed industries. And households, who aren't even paying for CO2 emissions. IMO, too much of the money is going back to the polluters, disincentivising any real investment in lowering their emissions, but I understand that there's a need for political compromise to get anything done.

I am under the impression that even without subsidies, coal will still be a much cheaper option then alternatives. Until we can find an energy source cheaper then coal, implementing a carbon tax is going to hurt standards of living/jobs.

[Zamfir]

I am under the impression that even without subsidies, coal will still be a much cheaper option then alternatives. Until we can find an energy source cheaper then coal, implementing a carbon tax is going to hurt standards of living/jobs.

Sure, if you replace coal power by something more expensive, than there is either less energy for the same money/resources, or the same power with less resources for other activities. Can't avoid that, since coal really appears to be unbeatably cheap.

But the long-term cost might be smaller than you think. Coal has the highest share of total kWhs produced in most countries, but its share in the total cost of power production is not proportional to that share. Coal has after all the lowest production cost per kWh. Non-baseload power is usually delivered from other sources, with higher cost per kWh (if only because their capital cost cannot be spread over 24/7 operation). At the extreme end you have peaker plants, that only run for minutes or hours a day to fulfill the peaks of demand. Those hardly contribute to total kWh produced, but they contribute far more than their share to the cost. And of course, the grid infrastructure costs money too, without generating any kWh itself.

I don't have hard number right now, but when coal produces for example 50% of the total kWh/year, it's share of the total cost of electricity production+distribution will be far less, but perhaps as low as 25%. So even if alternatives to coal plants (continuously running gas plants, coal plus carbon capture, nuclear, wind+more backup gas turbines) are twice as expensive, the cost of electricity goes up by only some dozens of percents. That's a real loss, but not the end of the world.

The trouble with that rosy outlook is that is is only true in the limit, if we gradually replace coal plants when they approach the end of of their economic life. If we replace plants earlier, we destroy a lot of already paid-for capital value on top of the higher running costs of the alternatives, and that potentially adds up to a lot. Who gets to bear that cost directly depends on the mechanism to enforce the closing of the plants, but you can bet the costs will eventually be distributed widely, since everyone owns part of power plants through their municipalities and banks and pension funds etc.

In short: gradually replacing all coal power is not necessarily a nightmare scenario in the long run. But they last for decades and decades, and replacing them before their time adds to the bill in the short run.

[Hawknc]

In addition to that, the goal isn't necessarily to replace coal with something like solar or wind - as nice as that would be, it's a long-term vision and not something that will happen any time soon. Australia has some of the dirtiest brown coal plants in the world and currently there's no incentive for the privatised companies that own them to replace them or even improve their efficiency. A price on carbon provides that incentive and makes changing to a more efficient coal-fired plant or a natural gas plant more cost-effective. Power generation also isn't directly compensated as it's not a trade-exposed industry, but acknowledging that power companies will pass these costs on to consumers, the government is providing assistance to lower-income families to bridge the gap, paid for by the carbon price collected from power companies.