So in my first couple posts I have talked about pipelines and fossil fuels, but people seem unwilling to accept my views on pipelines until I answer the big question: where do I sit on the topic of anthropogenic global warming (AGW).
Way back in 1859 John Tyndall demonstrated that selected gases including, water vapour, carbon dioxide and methane can intercept/absorb Infra-red (IR) radiation. A few years later Swedish chemist Svante Arrhenius did the first experiments/calculations to estimate how changes in the concentrations of carbon dioxide in the atmosphere should affect global temperatures. Since then the field of chemistry has refined the number and it is now generally accepted that that the direct climate sensitivity to carbon dioxide (excluding all positive or negative feedbacks) is roughly 1.2°C of warming per doubling of carbon dioxide concentrations. What that means is in the absence of feedbacks (positive or negative) every doubling of carbon dioxide concentration in the atmosphere should result in an increase in the global mean temperature of approximately 1.2 oC.
So what does this mean? Well overwhelming consensus in the field is that a majority of the observed warming from 1951 to 2010 (numbers from the IPCC 2013 Physical Sciences Report) can be attributed to anthropogenic increases in the concentrations of Tyndall gases in the atmosphere (I, and many others, find that term “greenhouse gases” imprecise. A recent suggestion has been to refer to these gases as “Tyndall Gases” which I find both appropriate and clean as the name carries no additional baggage). There are some contrarians who challenge this basic consensus, but it would be difficult to be considered a serious thinker in the field if you did not accept the basic chemistry of AGW.
Now given the chemical reality of AGW; the next research issue to be addressed deals with the equilibrium climate sensitivity of the atmosphere/biosphere to increases in Tyndall gases. The Intergovernmental Panel on Climate Change (IPCC) has this to say:
Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence). The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment reflects improved understanding, the extended temperature record in the atmosphere and ocean, and new estimates of radiative forcing.
– The IPCC includes an important footnote: No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.
So the IPCC says they do not have a best estimate for climate sensitivity and the manner in which models handle sensitivity and feedbacks remains a topic of furious debate and a tremendous amount of research. Every month a new paper is published that changes the best science on the topic.
On the extreme end of the warming side are those who believe in catastrophic anthropogenic global warming (CAGW). These individuals believe that climate sensitivity is at the highest end of the spectrum and a tipping point will be reached at some, still-to-be-defined, concentration of Tyndall gases in the atmosphere causing a positive feedback loop that will result in cataclysmic heating. The result will be a substantial change occurring over a very limited time frame (in tens of years rather than hundreds or thousands of years). That is how they translate the naturally expected 1.2°C of warming per doubling of carbon dioxide concentrations into increases ranging from 4.5 °C to over 6 °C per doubling. Proponents of CAGW insist that the tipping point is nigh and that we must decarbonize ASAP or risk probable extinction as a species.
I look at the issue differently, my graduate-level courses in global biogeochemical cycles identified that most geochemical cycles involve negative feedback loops that buffer changes. People like me are called “lukewarmers”. We do not assume that positive feedback loops dominate the system but rather a balance of positive and negative cycles are at play with the resultant effect being a relatively minor positive effect. Unsurprisingly, an examination of the historical record demonstrates that changes in global temperature have historically mirrored the direct IR absorbtion characteristics of the increases in the various Tyndall gas concentrations.
So when you read someone talk about the “consensus” understand what that word really means. There is an overwhelming consensus that humans are having an effect on the global climate, but the IPCC (the organization who define the consensus) says:
No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.
The issue is that in the scientific community the issue isn't settled. The absence of consensus on sensitivity doesn’t stop political and social activists who insist they know better than the climate scientists. As a numerate and scientifically literate individual, I am skeptical, not of the science, but of the purveyors of these political messages. I strongly believe we are affecting our climate and strongly believe we need to decarbonize our economy but that is definitely a topic for a different post.
On the extreme end of the warming side are those who believe in catastrophic anthropogenic global warming (CAGW).ReplyDelete
Who are these people? I'm sure there are some, but - in my experience - those who use the term CAGW the most, are those arguing that there are people who believe in CAGW, without ever indicating who these people actually are.
I look at the issue differently, my graduate-level courses in global biogeochemical cycles identified that most geochemical cycles involve negative feedback loops that buffer changes.
I'm not really sure what you're implying here. We're essentially pushing (forcing) the system away from it's current state. There is no obvious reason why anything should be acting to force us back to where we were prior to the increase in anthropogenic forcings. There's nothing special about that initial state.
There are many lines of evidence that suggest that the overall feedback response is positive and that it will amplify the warming. Water Vapour is positive and quite large. Lapse rate is negative and cancels about half the water vapour feedback. Albedo changes are positive but quite small at the moment. Clouds are the big uncertainty, but they can have both a positive effect (basically through blocking outgoing long-wavelength radiation) and a negative effect (increasing the albedo). However, the evidence at the moment is that the overall effect of clouds is small. Hence the net effect of feedbacks is positive and amplifies the warming.
People like me are called “lukewarmers”. We do not assume that positive feedback loops dominate the system but rather a balance of positive and negative cycles are at play with the resultant effect being a relatively minor positive effect.
Well, this is almost certainly wrong. Do you have any actual evidence to support this position?
Unsurprisingly, an examination of the historical record demonstrates that changes in global temperature have historically mirrored the direct IR absorbtion characteristics of the increases in the various Tyndall gas concentrations.
Again, what do you mean here. That feedbacks are positive and amplify the warming is entirely consistent with historical changes. You seem to be suggesting otherwise. Any actual evidence?
That is how they translate the naturally expected 1.2°C of warming per doubling of carbon dioxide concentrations into increases ranging from 4.5 °C to over 6 °C per doubling.
You do need to be a little careful here. The Equilibrium Climate Sensitivity (ECS) is defined in terms of fast feedbacks only (water vapour, lapse rate, clouds). The range for the ECS is something like 2 - 4.5K. There are, however, slow feedbacks (permafrost release, reduction in snow and ice cover, ...) that will likely increase the warming. There is a paper by Hansen that discusses this (but I can't quite find this at the moment) and suggest that the Equilibrium System Sensitivity (ESS) is maybe as high as 6K. It is slow and so will probably not influence us much this coming century, but that's no reason to ignore that the very-long-term warming could be substantially higher than ECS estimates suggest. If you read what I said carefully, you'll note I used "maybe as high as", not "definitely".
Who are these people?... without ever indicating who these people actually are.ReplyDelete
Are you seriously asking this question or being subtly ironic? Let’s start with 350.org which states in their documentation that there exists a need to return to 350 ppm or we will see a catastrophic collapse of civilization. I’m not sure how that could be described as anything less than CAGW. There are any number of similar organizations with similar campaigns out there including the David Suzuki Foundation in Canada (Santa will drown campaign), Greenpeace International etc.... The fact you ask this question indicates that you may wish to become more acquainted with the level of discussion on this topic outside the straight-jacket of academia.
I'm not really sure what you're implying here. ..However, the evidence at the moment is that the overall effect of clouds is small. Hence the net effect of feedbacks is positive and amplifies the warming.
Certainly there are many lines of evidence indicating the possibility that positive feedback mechanisms should be the determining feature. As I note, I tend to believe they will be positive but only minimally so and not in the range of 3 - 4 degrees necessary for CAGW proponents to be correct. The obvious rebuttal is the instrumental record. Models, dependent of your feedbacks, fail to predict current temperatures (they show limited skill). Rather the change in temperatures in the 50 years prior to the pause almost perfectly tracked the changes in total Tyndall gas concentration increases in the atmosphere. Certainly the literature is full of explanations for this phenomenon but until such time as the models can effectively extrapolate then there will be doubters.
Well, this is almost certainly wrong. Do you have any actual evidence to support this position?
Besides the data for the 50 years prior to the pause? As noted above, prior to the pause surface temperature increases mostly tracked the expected increases in Tyndall gas contributions. The differences indicate a likely minor net positive feedback and indicate that the lower end of the IPCC consensus range is the most likely scenario (in my opinion of course). You are, of course, free to disagree but my opinion is completely in line with the IPCC
Again, what do you mean here...feedbacks are positive and amplify the warming is entirely consistent with historical changes. You seem to be suggesting otherwise. Any actual evidence?
At some point you should both re-read what I have written and then re-read your basic atmospheric chemistry texts because what I am saying is entirely consistent with the underlying tenets of atmospheric chemistry and we do not have the time here to go into the level of detail that will clearly be needed to satisfy you on this point.
You do need to be a little careful here. ...If you read what I said carefully, you'll note I used "maybe as high as", not "definitely".
As I note, my prediction is well within the consensus range suggested by the IPCC. You are free to disagree, as do the authors who suggest that the higher end of the IPCC predicted range is the correct one. Ultimately, as I write in a later posting, I currently believe that the models need to be improved so they can better predict the future conditions. Given this and my strong belief in the lower range of the IPCC consensus range, I have emphasized work to improve ecological resilience through habitat protection while working towards a better mix of renewable energy alternatives. As I write in my blog, the current mix is the result of poorly thought out policies and in some cases are resulting in increased Tyndall Gas concentrations with the added issue of reducing ecosystem resiliency in the process.
Another point often overlooked is that the warming trend seen from the 1970's to the 1990's is almost identical in its slope to that from the 1920's to the 1940's. Clearly the earlier warming must have been natural, and yet we are expected to believe that the later warming was due to greenhouse gases. There is also good evidence that the world has been warmer than the present within the recent past such as in the Holocene (9000 to 5000 yrs ago) the Roman Optimum (500 to 900Yrs ago ) We must accept that there is much that we do not know, including what is causing the "pause". I am not denying that there could be a "greenhouse effect", but I do dispute that it is dominating the climate. The evidence says it is not.ReplyDelete