The Reason We Need To Agree Which Of Three Fundamentally Different Hypotheses Regarding The Role Of Human In The Climate System Is Correct

In our paper

Pielke Sr., R., K.  Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D.  Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E.  Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J.  Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases.   Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American   Geophysical Union.

we examined three hypotheses regarding the role of humans in the climate system. Only one can be correct. The three hypotheses are:

  • Hypothesis 1: Human influence on climate variability and change is of minimal importance, and natural causes dominate climate variations and changes on all time scales. In coming decades, the human influence will continue to be minimal.
  • 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.
  • Hypothesis 2b: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.

We concluded that Hypotheses 1 and 2b are rejected based scientific evidence.  Only Hypothesis 2a agrees with the scientific evidence.

In a July 5 2011 post by Mike Hulme titled

You’ve been framed: six new ways to understand climate change

he wrote

There are many ways to frame the phenomenon of climate change. Some may be more engaging and some more helpful than others. Some may play looser with the facts. And yet no frames – even those that remain faithful to the facts – can be entirely neutral with respect to the effects that they generate on their audiences.

Take the opening item in The Conversation’s recent climate change series Clearing up the Climate Debate.

This open letter boldly states its framing narrative: “The overwhelming scientific evidence tells us that human greenhouse gas emissions are resulting in climate changes that cannot be explained by natural causes. Climate change is real, we are causing it, and it is happening right now.”

Fact. Nothing to challenge there.

My Comment:  This statement in Clearing up the Climate Debate , however, does not tell anything about the distinction between Hypothesis 2a and 2b.  It is a flawed statement, therefore, because it is so incomplete.  What is implicit in their statement, however, is that human greenhouse gas emissions are the dominate climate forcing (i.e. that accept hypothesis 2b).

Mike Hulme continues

But how about this alternative?

“The overwhelming scientific evidence tells us that human greenhouse gas emissions, land use changes and aerosol pollution are all contributing to regional and global climate changes, which exacerbate the changes and variability in climates brought about by natural causes.  Because humans are contributing to climate change, it is happening now and in the future for a much more complex set of reasons than in previous human history.”

I’m confident too that none of my climate science colleagues would find anything to challenge in this statement.

My Comment: This is hypothesis 2a which is the only one that can not be refuted, as reported in Pielke st al 2009 and NRC 2005.

Mike continues

And yet these two different provocations – two different framings of climate change – open up the possibility of very different forms of public and policy engagement with the issue. They shape the response.

The latter framing, for example, emphasises that human influences on climate are not just about greenhouse gas emissions (and hence that climate change is not just about fossil energy use), but also result from land use changes (emissions and albedo effects) and from aerosols (dust, sulphates and soot).

It emphasises that these human effects on climate are as much regional as they are global. And it emphasises that the interplay between human and natural effects on climate are complex and that this complexity is novel.

My Comment: I agree with Mike Hulme, except that the first provocation is much too narrow and should be summarily rejected.  Policy responses based on a limited focus on greenhouse gas emissions, as a mechanism to influence how humans are impacting climate, will result in poorly thought out policy responses. 

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