11 November 2009

Alternative Hypotheses About Climate Change, Part 2

In Part 1 I laid out the three hypotheses as presented by 19 distinguished Fellows of the AGU an article in EOS (PDF, AGU membership required). In this post I present their selection, and some of their justification and discussion of implications. First they chose Hypothesis 2a:
Hypothesis 2a: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern during the coming decades.
Why did they pick this one over the others?
Hypotheses 2a and 2b are two different oppositional views to hypothesis 1. Hypotheses 2a and 2b both agree that human impacts on climate variations and changes are significant. They differ, however, with respect to which human climate forcings are important. Because hypothesis 1 is not well supported, our scientific view is that human impacts do play a significant role within the climate system. Further, we suggest that the evidence in the peer- reviewed literature (e.g., as summarized by National Research Council (NRC) [2005]) is predominantly in support of hypothesis 2a, in that a diverse range of first- order human climate forcings have been identified.
What are these other climate forcings?
In addition to greenhouse gas emissions, other first- order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005]. As with CO2, the lengths of time that they affect the climate are estimated to be on multidecadal time scales and longer.
Why does it matter?
Because hypothesis 2a is the one best supported by the evidence, policies focused on controlling the emissions of greenhouse gases must necessarily be supported by complementary policies focused on other first- order climate forcings. The issues that society faces related to these other forcings include the increasing demands of the human population, urbanization, changes in the natural landscape and land management, long- term weather variability and change, animal and insect dynamics, industrial and vehicular emissions, and so forth. All of these issues interact with and feed back upon each other. The impact on water quality and water quantity, for example, is a critically important societal concern. The water cycle is among the most significant components of the climate system and involves, for example, cloud radiation, ice albedo, and land use feedbacks [NRC, 2003]. Regional and local variations in water availability, water quality, and hydrologic extremes (floods and droughts) affect humans most directly.

If communities are to become more resilient to the entire spectrum of possible environmental and social variability and change [Vörösmarty et al., 2000], scientists must properly assess the vulnerabilities and risks associated with the choices made by modern society and anticipate the demands for resources several decades into the future. Moreover, since the climate, as a complex nonlinear system, is subject to abrupt changes and driven by competing positive and negative feedbacks with largely unknown thresholds [Rial et al., 2004], scientists’ ability to make skillful multidecadal climate predictions becomes much more complicated, if not impractical.
Surely the IPCC is on top of this? The authors suggest not:
The evidence predominantly suggests that humans are significantly altering the global environment, and thus climate, in a variety of diverse ways beyond the effects of human emissions of greenhouse gases, including CO2. Unfortunately, the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment did not sufficiently acknowledge the importance of these other human climate forcings in altering regional and global climate and their effects on predictability at the regional scale. It also placed too much emphasis on average global forcing from a limited set of human climate forcings. Further, it devised a mitigation strategy based on global model predictions. For example, although aerosols were considered as a global average forcing, their local effects were neglected (e.g., biomass burning, dust from land use/land cover management and change, soot from inefficient combustion).

Because global climate models do not accurately simulate (or even include) several of these other first- order human climate forcings, policy makers must be made aware of the inability of the current generation of models to accurately forecast regional climate risks to resources on multidecadal time scales. For example, how the water cycle responds to the diversity of climate forcings at the regional level will be important information to policy makers seeking to mitigate risks to water resources.

We recommend that the next assessment phase of the IPCC (and other such assessments) broaden its perspective to include all of the human climate forcings. It should also adopt a complementary and precautionary resource- based assessment of the vulnerability of critical resources (those affecting water, food, energy, and human and ecosystem health) to environmental variability and change of all types. This should include, but not be limited to, the effects due to all of the natural and human causedclimate variations and changes.


  1. Al Gore seems to be ahead of this game. He has been taking lesson from NASA GISS on soot. He is being paid to promote carbon trading and globalisation. Will this affect policy ? I very much doubt it.


    Gore, backed by government ministers and scientists, said that the soot, also known as "black carbon", from engines, forest fires and partially burned fuel was collecting in the Arctic where it was creating a haze of pollution that absorbs sunlight and warms the air. It was also being deposited on snow, darkening its surface and reducing the snow's ability to reflect sunlight back into space.

  2. My upcoming paper in Bulletin of the American Meteorological Society (BAMS) titled 'Achieving Climate Sustainability' - available in the early online edition at http://ams.allenpress.com/perlserv/?request=get-toc-aop&issn=1520-0477 (see Sep 16) - lays out the societal and policy consequences of this broader view of what constitutes human climate forcing. Rather than undermining the need to act on greenhouse gas emissions, it extends the range of actions that must be considered.

  3. The group asserts (without further explanation) that:
    “hypothesis 1 is not well supported”

    I don’t buy it.

    Perhaps the group could elaborate and/or show me where -- in their view -- my brief summary (and more detailed set of evidence) is wrong.


  4. Roger -- am I correct in my understanding that the difference between Hypothesis 2a and 2b is largely a matter of scale? That is, in 2a are the "diverse range of climate forcings" that are in addition to greenhouse gases mostly those forcings that operate mainly at regional scales?

    Thanks, Allan

  5. Question - is it possible to present a chart with the various first order forcings with a percentage of contribution (and error bars maybe) to the AGW part of warming for both 2a and 2b? It would be good to compare just how significant these differences are. Without that, it's hard for me to determine just how critical the difference is.

  6. -5-Dean

    Here is a reply from Pielke Sr.:

    "Dean - With respect to positive global average radiative forcings, I have estimated the contributions of (without error bars, however) in my presentation in slide 12 at

    Pielke, R.A. Sr., 2006: Regional and Global Climate Forcings. Presented at the Conference on the Earth’s Radiative Energy Budget Related to SORCE, San Juan Islands, Washington, September 20-22, 2006. http://www.climatesci.org/publications/presentations/PPT-69.pdf

    I found that the radiative effect of CO2 was about a 27% effect (of the total radiative warming including solar).

    However, climate forcings can be first order (in that they alter weather patterns significantly) even in the absence of a global average radiative forcing. Our EOS article provided examples of climate forcings which fit this much needed broader definition in terms of societal and environmental effects.

    We currently do not have generally accepted metrics to quantify the different forcings. In the 2005 NRC report 'Radiative forcing of climate change: Expanding the concept and addressing uncertainties" the need for such metrics was recommended as one of the major findings.

    In the metric we proposed in

    Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974. http://pielkeclimatesci.wordpress.com/files/2009/10/r-312.pdf

    the radiative effect of aerosols, in terms of how atmospheric pressure gradients are altered, was about 60 times larger than the radiative effect from CO2.

    Roger Sr."

  7. Received by email for posting as a comment:

    "I read the full EOS essay, and it was a clearly written exposition of the views not only of your father, but many other professional earth scientists including myself. I seriously doubt a large group of earth scientists actually disagree with hypothesis 2a. Unfortunately, politics and economic philosophy are swirled in with the science, and it is really hard to separate sound science from inherent policy implications (me included). For a large group of people who disdain the idea of a self-ordering principle in human social and economic exchange and actions, there seems to be a strong need to affirm 2b despite both a priori rationale and strong empirical evidence that this hypothesis is deeply flawed. Coincidentally, 2b most intuitively seems to find its apparent policy solution in the form of centralized command and control of the economy, in order to carry out effective mitigation of greenhouse gases. What is too easily forgotten or ignored however, is that centralized control suffers incredible inefficiency and moral hazard since it is always plagued by at least three almost insurmountable difficulties. Firstly, there is a very real and daunting “knowledge problem”. Much like the problem faced by a weather forecaster, it is almost impossible for a planner to accurately initialize the current situation. This assures that centralized policy actions will always carry with them unforeseen consequences, often negative. Secondly, centralized command suffers from the "rubber arm" syndrome. Even armed with hypothetical perfect knowledge of intial conditions, it will most often lack an effective strategy and the means to implement good policy response. Thirdly, there is the important issue of "concentrated corruption" and special interests. In a state controlled economy, the most powerful and connected are always able to purchase "loopholes" in the law for themselves, thus using the bureaucratic structure for their own advantage against their competition. Thus the social justice sought by well-meaning people quickly turns into the oppressiveness of an oligarchy for the rich and powerful. Obviously, I am not a social scientist, but it seems so completely clear to me that international law-making bodies vested with distributing some type of hypothetical "egalitarian global climate" are certainly doomed to fail miserably, owing to all three policy issues I raise above.

    It is high time many well-intentioned people (physical scientists included) wake up to the reality that 2b never has been a robust scientific view of climate change. Instead, the flawed 2b hypothesis is being used as a battering ram by some politicians (and aided by a certain group of scientists of the same ideological brand), all too willing to foist a repressive and ineffective form of centralized government upon many well-intentioned and sincere citizens.

    Best Regards,

    Bryan Sralla"

  8. -7-Bryan Sralla,

    1) Well said…

    2) It appears we agree that the threat presented by a government “fix” FAR exceeds any threat (real or imagined) presented by climate change.

    3) The evidence suggests that -- just like you and I -- the large majority of our fellow scientists do not support CO2 regulation.

    P.S.) Roger - you might like that first link, especially the discussion on hurricanes.

  9. Roger,

    I wanted to go back to this because of the post your father just put up which references in the hypotheses. I thought when I first read the options and continue to think that there is a massive gap between 1 and 2(a). What is "minimal" supposed to encompass in 1? And what is meant by "significant" and "concern" in 2(a)?

    Because I think these folks make a huge leap to go from picking 2(a) to then stating that the choice of 2(a) therefor necessitates the implementation of all kinds of policies.

    My choice -- your father and others have shown that man does lots of things that can have an impact on climate. We have no idea what the net effect of all these things are. It would be a good idea to study these and a lot of other things in reference to climate. When we get a whole lot better handle on our understanding, we can begin to start sorting out what might be done and at what cost. That's when we get a WHOLE lot better understanding.

    How 'bout 1(b)? There might well be lots of human influence, but we just don't understand enough yet. Let's not do anything stupid until we do.