Arguments
Is there a scientific consensus on global warming?
The skeptic argument...
There is no consensus
The Petition Project features over 31,000 scientists signing the petition stating "There is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere ...". (Petition Project)
What the science says...
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97% of climate experts agree humans are causing global warming. |
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Science achieves a consensus when scientists stop arguing. When a question is first asked – like ‘what would happen if we put a load more CO2 in the atmosphere?’ – there may be many hypotheses about cause and effect. Over a period of time, each idea is tested and retested – the processes of the scientific method – because all scientists know that reputation and kudos go to those who find the right answer (and everyone else becomes an irrelevant footnote in the history of science). Nearly all hypotheses will fall by the wayside during this testing period, because only one is going to answer the question properly, without leaving all kinds of odd dangling bits that don’t quite add up. Bad theories are usually rather untidy.
But the testing period must come to an end. Gradually, the focus of investigation narrows down to those avenues that continue to make sense, that still add up, and quite often a good theory will reveal additional answers, or make powerful predictions, that add substance to the theory.
So a consensus in science is different from a political one. There is no vote. Scientists just give up arguing because the sheer weight of consistent evidence is too compelling, the tide too strong to swim against any longer. Scientists change their minds on the basis of the evidence, and a consensus emerges over time. Not only do scientists stop arguing, they also start relying on each other's work. All science depends on that which precedes it, and when one scientist builds on the work of another, he acknowledges the work of others through citations. The work that forms the foundation of climate change science is cited with great frequency by many other scientists, demonstrating that the theory is widely accepted - and relied upon.
In the scientific field of climate studies – which is informed by many different disciplines – the consensus is demonstrated by the number of scientists who have stopped arguing about what is causing climate change – and that’s nearly all of them. A survey of 928 peer-reviewed abstracts on the subject 'global climate change' published between 1993 and 2003 shows that not a single paper rejected the consensus position that global warming is man caused (Oreskes 2004).
A follow-up study by the Skeptical Science team of over 12,000 peer-reviewed abstracts on the subjects of 'global warming' and 'global climate change' published between 1991 and 2011 found that of the papers taking a position on the cause of global warming, over 97% agreed that humans are causing it (Cook 2013). The scientific authors of the papers were also contacted and asked to rate their own papers, and again over 97% whose papers took a position on the cause said humans are causing global warming.
Lead author John Cook created a short video abstract summarizing the study:
Several studies have confirmed that “...the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes”. (Doran 2009). In other words, more than 97% of scientists working in the disciplines contributing to studies of our climate, accept that climate change is almost certainly being caused by human activities.
We should also consider official scientific bodies and what they think about climate change. There are no national or major scientific institutions anywhere in the world that dispute the theory of anthropogenic climate change. Not one.
In the field of climate science, the consensus is unequivocal: human activities are causing climate change.
Last updated on 16 May 2013 by dana1981. View Archives
When you (indirectly) accuse others of being sheep, be careful your argument is not wooly.
"Los Alamos National Laboratory is hosting the Third Santa Fe Conference on Global and Regional Climate Change Oct. 31 thru Nov. 4. A lot of good science has come out of LANL, but the conference program is dismaying. I’m not familiar with many of the names on it, but I do know a few of them, e.g. Lindzen, Singer and Monckton! What can the conference organizers be thinking?"
In response, Gavin pointed out that one of the organizers is Petr Chylek, who leads a Remote Sensing team at LANL. It appears Chylek is attempting to bolster the scientific credibility of AGW denial, as he has done this kind of thing before. His strategy may backfire, by diminishing LANL's reputation for producing high-quality science.
I do think 'consensus' that some variable is changing can apply to a wide range of estimated values so long as that range does not include zero. There has been for many years a large range on estimated climate sensitivity (e.g. the oft-quoted 2C-4.5C per doubling CO2).
I want to give another example where there was, for a great many years, a lot of uncertainty in the magnitude of a value, yet the existence of the change it implied was not questioned. For many years, there was a large range for estimated values of H0, the expansion rate of the Universe, which only recently has been narrowed down considerably.
As recently as 1996, there were estimates as low as 40km/s/Mpc and as high as 100km/s/Mpc, it is now closer to 74km/s/Mpc. Edwin Hubble's initial estimate in 1929, after he first measured the redshift of spectral lines in Cepheid variables, was 500km/s/Mpc. Was there consensus in 1996 that the Universe is expanding? There certainly was. Was that based on a tightly-constrained value for the expansion rate? Absolutely not.
I disagree that just because a value is not zero, that there is a consensus among all players. Do you really believe that Lindzen, who published that the climate sensitivity is 0.5, Link - 1.1, Spencer - 1.3, Annan - 3, Hansen - 6, and Pagani - 9.4 are all in agreement? This seems odd to me, especially since there are many from this site who constantly argue against Lindzen and Spencer (and anyone else who claims a low climate sensitivity). Do you really believe that they are part of the "consensus" just because their values are nonzero?
Of course Spencer won't agree, but that is becuase his estimate of climate senistivity lies outside the range considered plausible by the mainstream consensus view. Note Spencer would have a hard time explaining many paleoclimate events with such a low sensitivity, which is why the concenssu is that a value that ow isn't plausible.
There is little agreement on the range of climate sensitivity values (the most commonly quoted ranges are 2-4.5, 1.5-4.5, and 1.5-5). With the exception of James Annan, the five scientists I mentioned in my earlier post are all outside this range, and there are others which make claims of even higher and lower values. Sure, Spencer will not agree, but I doubt that Hansen will either.
There appears to be a misconception on the other thread that since scientists agree that CO2 has contributed to warming, that there is a consensus as to how much.
The point is that the concensus is on the range of plausible values, not on the individual point estimates. This is actually a good way to narrow down the uncertainty of the estimate of climate sensitivity by performing research that places constraints on climate sensitivity, beyond which they are not plausible (or inconsistent with the observations). I rather suspect that the Pagani value for instance is not a estimate of the most likely value, but an upper bound resulting from some physical constraint.
BTW, climate sensitivity is not specific to CO2 radiative forcing, it applies more or less equally to any other forcing.
Using ranges is a very good way to narrow down uncertainties in many instances. For such a complicated scenario, different methods are used in an attempt to ascertain the most likely value (or range of values).
In genetics, significant research has been able to narrow down the genes responsible for specific traits. Initially, there would be no consensus, but as pieces were placed together, a general picture appeared, resulting in an agreement among the scientists involved. At some point, you could say a consensus occurs, because the scientists agree that certain genes are responsible, without nailing down the specifics. The point at which that occurs may be somewhat nebulous.
The same could be said for climate science. At what point can we say there is a consensus on climate sensitivity? My conclusion is that the range is still too wide to claim a general agreement. Some have tried to narrow the range, but then lose enough scientists to preclude calling it a consensus.
BTW, the Pagani value was determined from paleo measurements, and Hansen and Sato (2011) recently stated that fast climate sensitivity was 3, while equilibrium climate sensitivity was 6. Excluding the Pagani value, with may not e relevant to today anyway, to claim a consensus opinion on the range of climate sensitivity, one would have to choose values from ~1-7! IMO, this does not constitute a consensus.
Of course there is no agreement on a specific value for climate sensitivity, nobody is claiming that there is, and indeed it is an unreasonable expectation. However that doesn't mean we can't have a concensus on the spread of plausible values.
Note that a spread of plausible values is what we need for impacts studies, so that the distribution of plausible loss properly incorporates our uncertainty regarding climate sensitivity.
You need to get away from the idea that we need to know the exact value of climate sensitivity.
I note that your comment regarding the Pagani value does not address the question as to whether it is a most probable value or a bound.
I guess it comes down to what we understand to be the range of plausible values, and if that range is sufficient to state that there exists a consensus. I am not comfortable making that claim at this time, as I would prefer to see a narrower range of plausible values before making that assertion. Also, I do not believe that scientists would agree on the range. This does not mean that a consensus could not be formed in the future. I do not need to know the exact value, but the concept that the high end of the range is a factor of three higher than the low end implies that we still have a long way to go. Given the EPA range of atmospheric CO2 to lie between 535 and 983 by 2100, the resultant temperature increase lies in the range is 0.5 - 7.0 C (low-low to high-high).
The pagani value was a calculated number for three different times in the recent geological past: 7.1 +/- 1.0, 8.7 +/- 1.3, and 9.6 +/- 1.4 C/doubling.
http://earth.geology.yale.edu/~mp364/data/2009%20Pagani%20et%20al.pdf
Your comment on the Pagani estimate(s) still doesn't clarify whether it is a bound or an estimate of the most likely value.
Hansen estimated equilibrium sensitivity at ~6°C? So while the Pagani numbers are rather higher, they are really not directly relevant to the short term transient sensitivity of 3°C. Also, keep in mind that the high end of the sensitivity tail is much less determined than the low end.
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This is all smoke and mirrors on your part anyway, Jonathon. The consensus on values and ranges come from the evidence - if you wish to assert a climate sensitivity outside that range, present some evidence, not a petition.
I am not missing the point. I never said that there is a consensus on the exact value, so you can stop repeating yourself on this issue.
I have yet to see anything that support a consensus on the range of plausible values, and highly doubt that one exists. Typically the evidence against a consensus is to present data which does not conform, which I have already done.
The Pagani estimates are estimates of the value, not a bound. The uncertainties listed after each value are his calculated range. Clear?
Philippe,
When assembling a range of value such as this, each individual measurement is assigned the same probability, assuming they were determined independently, just like rolling the dice. If additional research yields values which begin to cluster around a specific range, then we can assign higher probability to those values. In the case of climate sensitivity, we see values clustered not around a mid-range value, but at the high and low ends, but still yielding a similar mid-range value. This anti-Gaussian distribution would indicate that the mid-range value is less likely than either end.
Also, in consensus. Am I correct in assuming that in your mind, if there is a published value outside a consensus range, even in a refuted paper, then consensus doesn't exist?
(-Snip-).
The Hansen value can be found here among other places:
http://www.skepticalscience.com/Climate-emergency-time-to-slam-on-the-brakes.html
Muon,
We are discussing the range, not a value.
[DB] Inflammatory snipped.
If the range of plausible values for the Hubble Constant is 55-80km/s/Mpc, is there a consensus that the Universe is expanding? Yes or no?
"climate sensitivity" = short-term transient sensitivity = fast feedbacks = 3 deg C
The 6 deg C figure you keep providing is for long-term sensitivity / slow feedbacks.
We already answered that on the other thread - yes. The discussion here is about whether we can say that there is a consensus among scientists as to the sensitivity of the temperature to CO2. We have already agreed that exact value in unknown, and that there is a plausible range of values. The disagreement is about what is that range, and is it narrow enough to constitute a consensus. Your range for the Hubble is much narrower, and not being a cosmologist, I cannot appropriately answer your question.
Biblio,
If we are talking about short-term transient sensitivity, then the plausible values are much lower, and Hansen's value of 3 is still on the high side. The following might help clear this up for you.
http://profmandia.wordpress.com/2011/01/18/clearing-up-the-confusion-about-climate-sensitivity/
http://journals.ametsoc.org/doi/abs/10.1175/2011JCLI3989.1
as far as I can see you have provided no evidence that there is substantial disagreement regarding the range of plausible values, just that there are point estimates that are not in close agreement..
"and is it narrow enough to constitute a consensus."
The spread of the range of plausible values has no bearing whatsoever on whether there can be a concensus on what the range actually is. If we had some dimensionless quantity that physics constrained to be strictly positive, but otherwise we knew nothing about it, then it would be perfectly reasonable for the concensus to be that the plausible range were from 0 to +infinity.
That is for equilibrium climate sensitivity. I though you were talking abobut transient sensitivity, which the first article states as 1-3, while the second says 1.3-2.6. In either case, 3 is on the high side for transient sensitivity.
Please read more carefully.
The argument that everyone is in agreement, because we all think that the value is positive, is nice, but does not tell us much. If that is the extent of the consensus, then we should just drop it altogether. Since no one wishes to go beyond that issue, there is really no point arguing any further.
Your argument is essentially a straw man, I don't particularly see any point in arguing about it either, but if you change your mind, please take it to a more appropriate thread.
Your entire rant is simply muddying the waters of what a definition of consensus might mean. As has already been explained and discussed, science doesn't really ever bother with defining and delineating a consensus. The consensus simply is. It is whatever most people in the field understand and agree with. There are always some who agree with X but disagree with Y, or vice versa. There's always a Z that's so basic and given that everyone but crackpots agree with it, and a W that's so far out of the mainstream that no one takes it seriously.
The point is that there is no structure. Scientists don't get together once a year at the annual consensus convention and vote on which parts of science will or will not be considered accepted.
Scientists get up in the morning. They go to work. They study, research, think and publish, and read each other's papers. Over time, like a hive mind, a social network of understanding evolves.
What you are doing with the range of climate sensitivities is to muddle that, by taking the simple idea that every scientist has what he believes is a likely range of sensitivities, and instead conjuring a world where each scientist picks a specific number, and then claiming that because there are so many different numbers, there cannot be a consensus.
This is all typical denier nonsense, intended to confuse people and sew doubt.
The bulk of scientists know what the likely range of sensitivities is. A small group of fringe scientists expect sensitivities outside of that range.
This does not mean that scientists are at all confused on the issue (which is what you ultimately are trying to imply with your own personal redefinition and portrayal of a consensus).
You are a little late to the party, so I will bring you up to date.
1. The claim has been made here that since atmospheric CO2 leads to increasing temperature that there is a consensus on climate sensitivity, and it is positive.
2. The claim has also been made that the actual range which makes up the climate sensitivity is irrelevant, as long as we all agree on the endpoints of that range.
3. The final claim is that we all agree on that range.
I disagree with all three claims. The first two claims are simply ridiculous, as they have no real meaning. It is not enough to know that X influences Y, but we need to know how much X influence Y, and if the influence of X on Y is unlimited, then do we really know anything about X and Y?
The third claim is the only one with any real meaning. It is not sufficient for a small group to agree on a range if others do not, and calling Link, Spencer, Pagani, and Hansen "fringe scientists" does not add to your credibility. If you wish to add anything further, I suggest you tone down your attitude and try to become scientific in this discussion.
[DB] "If you wish to add anything further, I suggest you tone down your attitude and try to become scientific in this discussion."
Good advice; please embody it yourself so others may emulate your positive example.
By disagreeing with 'claim number one,' are you suggesting that sensitivity is either 0 or negative? If so, you would do well to refer to a sensitivity thread.
But you have created new goalposts in the other two of your three claims: 'we all agree.' There is no such specific language in the definition of consensus as 'general agreement.'
This is similar to the artifice used by the petition project, which contrived this language:
there is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere"
Such language as 'convincing,' 'forseeable,' and 'catastrophic' are non-scientific. And 'we all agree' is higher than most legal burdens of proof.
See posts #475, #470, #456, and #454 for your answer.
Remember, it was the other posts here at SKS who came up with claims, not myself.
You would also be wise to learn that Webster defines consensus as "general agreement." If posters here are defining consensus as something else, then that would be reason for confusion.
'General agreement' was exactly how I defined consensus. You have added 'we all agree,' which requires unanimous consent - a goalpost shift if ever there was one. I doubt you will ever find that.
No, I'm not late to the party. I've read all of the comments. You missed my point.
You are the one who is making propositions which others on this thread then try to recast into reasonable statements. You ignore their input and go on and on with your own peculiar interpretation of events as if you are speaking a different language, or rather speaking and not listening.
I will repeat: You are personally redefining "consensus" in a way that lets you claim that there is none. The problem lies in your personal definition of consensus.
There is a consensus that climate sensitivity is positive. The only people who try to imply otherwise are Lindzen and Spencer, but I don't think that even they would be caught dead actually coming out and saying such foolishness.
There is a vague consensus around the likely range of climate sensitivity, based on the growing number of studies that all seem to fall in the 2˚C-4.5˚C range, centered somewhere around 3˚C. You can use the search button at the top of the page to find, read, and argue about such claims.
But the point here is consensus. There is a growing consensus, resulting from a growing body of mutually confirming evidence using multiple sources and observations, which helps to bracket likely climate sensitivity.
That you refuse to accept this consensus does not dissipate it one whit. That you choose to try to cast the term "consensus," the actual nature of such a consensus, or the body of knowledge behind said consensus into your own "we don't know, we can't know, we should wait" paradigm again does not dissipate the actual consensus one whit.
[snip] Is that your only issue here? That I used we all agree instead of general agreement?
If you want to debate the existence or validity of 'consensus,' then it is critical to set a standard. Do you not see the difference between 'general agreement' and 'we all agree'?
For example, there is probably 'general agreement' among regular readers here that the Oregon Petition is a waste of time. However, I would not say 'we all agree' about that.
Any confusion between 'we all agree', 'general agreement' and 'consensus' was unintentional.
Note, too, that unsubstantiated claims such as yours carry little validity and make you seem as if you are not very well versed in this science. Use of terms such as 'warmist' doesn't help make your case either.
Perhaps you could start by reading the original post, which deals with the idea of 'consensus' among scientists, not 'convergence' of climate models. Follow that by a thorough reading of the Comments Policy; if you cannot abide by that policy, your comments should indeed be deleted.
The thread about modeling, if you care to have a look, is #6 on the 'Most Used Climate Myths.' Read and learn. Then start asking questions; you'll find most here are glad to engage in reasonable debate. However, if you are here to just throw around jargon, make unsupported claims and lecture about your views on 'uncovering the truth,' you're wasting everyone's time.
You posted a link that, combined with your interpretation of it, demonstrates that you don't understand how modeling or science work.
Climate science is of course inexact due to the large number of variables and the difficulty in measuring them. As a result, predictions must cover a broad range. This does not devalue the predictions or imply a lack of confidence or understanding.
You don't complain when the weatherman tells you it will rain tomorrow, but does not accurately predict that the first raindrop will arrive at exactly 3:37 PM.
Your observations and complaints in three posts add no value. They advance nothing.
They pretty much make you sound like you're really grouchy, and climate science is telling you something you'd rather not hear.
That, in and of itself, is nothing new. Lots of deniers do it day in and day out.
Do you have anything substantive and meaningful to post, or to ask?
Here's a good explanation of the additive uncertainty http://www.nature.com/climate/2010/1002/full/climate.2010.06.html introduced by lots of factors that each have their own uncertainty. Having a model that produces a number or a small range in a 100 year climate forecast is impossible.
I'm short of time, but lets sort some basics. What model tells you what climate (30 averages of weather) do, given a particular emission scenario. They obviously cannot predict what humans will do - that is for politicians to decide. Its like firing a cannonball. If you choose this angle, then you get this trajectory. However, the force from the gunpowder is subject to uncertainty so the exact landing spot has uncertainty too.
The uncertainty is qualified - and shown on the IPCC predictions. It seems to me that you believe that the modellers make claims that no published science in fact makes. You could learn what the models actually do and what they predict. Then you can discuss sensibly what models can and cannot do. Until you do that, your argement makes no sense. You are attacking a strawman - a common tactic. Please go to the "Models are unreliable" thread, and take from there after you have learnt a bit.
No serious scientist deletes posts that disagree with their viewpoint. This magazine labels these as political or even more ridiculously that they're off topic and removes them.We know how much greenhouse gas has been produced by mankind, so assuming that the growth rate continues on trend, then you should be able to predict with a good degree of confidence what the global mean temperature will be in a relatively short time period, 5 years say. If you can't do this, and say that there are too many factors - mankind and nature - that prevent any level of confidence being attributed to your predictions, then your predictions are practically useless. There is still no concensus amongst warmists as to which greenhouse gas is the main culprit. Is it CO2 or methane? Both of which, of course, have both manmade and natural sources.[DB] "If you can't do this"
Straw man argument. Even removing exogenous factors such as volcanic effects and oceanic cycles, a trend of much more than a decade is typically needed for the underlying warming signal inherent in multiple metrics used to monitor global warming due to the noisy nature of the data.
"There is still no concensus amongst warmists as to which greenhouse gas is the main culprit."
100% incorrect. You will need to actually educate yourself more on this topic to understand just how wrong this statement is. This is the equivalent of saying that 2+2=a porcupine.
Trolling comments struck out. Future comments of this nature will be simply deleted. FYI.
[not DB] Use the Search box to look for "methane" without the quote marks. Then search for "Scientists can't even predict weather."
[DB] "Science is about trying to establish truth by coming up with theories and then demonstrating that new data meets the prediction that the theory made."
Imprecise; science is about developing an explanation (a hypothesis) that best explains what we can see and measure. Tests are then devised to either support or disprove the hypothesis. Those hypothesis that withstand the test of time and much research are then called "theory". One such is the theory of gravity. Another is the theory anthropogenic global warming. This link may help.
"Creating a site where only warmists are allowed to attack arguments that critics of the science (labelled as denialists) have pointed out is not science."
Two misconceptions here. This site was created to debunk the logical fallacies of those who pretend to try to poke holes in the research by ignoring the evidence which contradicts their position. The second misconception is that the term denialist refers to those who ignore evidence contrary to their position, no matter how damning. If you prefer, substitute the term fake-skeptic on those occasions you encounter the term "denialist" on this website. They are interchangeable.
The remainder of your comment, unfortunately, devolves into ideology and misunderstandings of what science is, and isn't. Please read the Comments Policy.
[not DB] Use the Search box to search for "models are unreliable" without the quote marks.
I have never encountered such a debate as what we have on climate change that is so emotionally charged, however. This website is setup to try to debunk arguments put forward by all and sundry who've spotted holes in the warmist arguments, and there are lots of them. It will naturally attract people who agree and disagree with you. (-Snip-) I don't believe that warmists are a collective group, they represent a range of views of which the only concensus is that they believe that the earth will get warmer due to mankind. There is no concensus on how much warmer, which manmade pollutants are the primary cause of global warming etc.
[DB] "and there are lots of them."
Unsupported assertions. Be specific, put your objections on the appropriate threads (use the Search function; 4,700+ threads exist here).
Your use of the terms "warmists" betrays ideology. Please study the Comments Policy & constructe future comments for better adherence to it. Future ideological and/or inflammatory comments will simply be deleted and your posting privileges may be curtailed.
Your use of the term "concensus" shows a lack of understanding of the scientific use of the term.
Inflammatory snipped.
The high end of the range includes some "slow" feedbacks like permafrost melting and releasing CO2 and methane. Since that is already happening those are not necessarily slow anymore but there is considerable uncertainty about the future amounts. The darker line inside that range is the current best estimate. The amounts and types of uncertainty around that best estimate are difficult to depict in such a simple chart, and it is worth reading some of the details in the text.
For your comments about this website, there are actually quite a few threads that address some of your bones of contention. For example making predictions for 5 years involves climate but also weather and is addressed here Even the difference between skepticism and denial was discussed here. I suggest you read the comments below the opening piece because you will probably find that all or most of your arguments have been offered and responded to there. If you disagree with the response then maybe you should add to that thread.
As I've mentioned in my last post, I'm fine with the demand that mankind reducing pollution but I'm not ok with calling a theory, scientific fact.
What exactly is my supposed political agenda here?[DB] Please refrain from introducing politics into the discussion. This is not a thread devoted to politics & climate science (others do exist that cover that).
Also, your discussion of models is off-topic on this thread. Please use the Models are unreliable thread for that. Thanks!
[DB] Moderation complaints snipped.
Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.
Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive or off-topic posts. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
Finally, please understand that moderation policies are not open for discussion. If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.
Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter.
Also, arguments about science need to proceed from discussion of data and publications, not misinformed opinion. So, in keeping with topic of this thread, perhaps you could tell us on basis you make this statement? "There is still no concensus amongst warmists as to which greenhouse gas is the main culprit.". As far as I know, this is flat out wrong. Show me otherwise.
"A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases (GHGs), such as chlorofluorocarbons, CH4, and N2O, not by the products of fossil fuel burning, CO2 and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO2 GHGs has declined in the past decade. If sources of CH4 and O3 precursors were reduced in the future, the change in climate forcing by non-CO2 GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO2 emissions, this reduction of non-CO2 GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition-specific long-term global monitoring of aerosol properties."
Global warming in the twenty-first century: An alternative scenario
James Hansen,*† Makiko Sato,*‡ Reto Ruedy,* Andrew Lacis,* and Valdar Oinas*§
June 16, 2000