The 2-Deg Global-Warming Limit

UPDATE:  At the end of the post, I’ve added  the graph being used as the Feature Image at WUWT.

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Politicians from around the globe gather annually in the UNFCCC meetings so they can propose and fail to come to worthwhile agreements on how to limit global warming and its impacts.  Year in, year out, same thing.  For the results of the most recent failed gathering, see the WattsUpWithThat post GWPF Welcomes Non-Binding And Toothless UN Climate Deal.  One of the primary factors that drive the politicians is an attempt to limit global warming to 2-deg C above preindustrial values, where preindustrial is considered the mid-to-late 1800s.

But where did that 2 deg C limit come from?

Some people might be surprised to discover that it started with a Professor of Economics, Dr. William Nordhaus of Yale, back in 1970s, not from a comprehensive analysis of climate, weather, sea levels and so on by climate scientists.  At least that’s what was presented in a blog post that has gained attention around the blogosphere.

The blog post is Two degrees: The history of climate change’s ‘speed limit’ by Mat Hope & Rosamund Pearce at ClimateCentral TheCarbonBrief. They write:

In the 1970s, Yale professor William Nordhaus alluded to the danger of passing a threshold of two degrees in a pair of now famous papers, suggesting that warming of more than two degrees would push the climate beyond the limits humans were [sic] familiar with:

And they quote Nordhaus:

“According to most sources the range of variation between between distinct climatic regimes is on the order of ±5°C, and at present time the global climate is at the high end of this range. If there were global temperatures more than 2° of 3° above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.”

Hope and Pearce then note how James Hansen discussed “dangerous” climate change during his 1988 presentation to Congress, but didn’t present a threshold, and that it wasn’t until 1990 that there was a study to support the 2-deg limit. It came from the Stockholm Environment Institute (SEI), in their report Responding to Climate Change: Tools for Policy Development [Part 1 of 2].  As noted in its introduction, it was:

…devoted to three specific aspects of the issues involved in developing policies for responding to climate change.

Oddly, the First IPCC Assessment Report was published a year later and it was inconclusive, inasmuch as the scientists could not differentiate between manmade and natural warming.

Hope and Pearce’s post at ClimateCentral TheCarbonBrief then run through the remaining history of studies working to support the 2-deg limit, one first presented by an economist.

That brings us to the post here by Pierre Gosselin at the NoTrickZone. It includes a number of quotes from members of the climate science community about the 2-deg C limit.  My favorite is the translation of a speech by Dr. Hans von Storch, in which von Storch is reported to have said in 2011 (my boldface):

We are in a time where scientists and politicians claim, or at least suggest, the science, in the form of the IPCC, or the German Advisory Council on Global Change (WBGU), has shown that the 2°C target is scientifically mandatory, and is thus no longer a political question that has to be negotiated by society, but rather a target that policymakers only must execute – quasi an order. However the IPCC has never in any way presented the 2°C target as mandatory. Rather this was done by a few scientists, or shall I say: politicians disguised as scientists.

That reminded me of a quote from Dr. Richard Lindzen, an Alfred P. Sloan Professor of Meteorology (emeritus) at the Massachusetts Institute of Technology.  A recent April, 2014 presentation to the European Institute for Climate and Energy (EIKE) by Dr. Lindzen can be found on YouTube here.  Early in the presentation, Dr. Lindzen states:

…it should be recognized that the basis for a climate that is highly sensitive to added greenhouse gasses is solely the computer models. The relation of this sensitivity to catastrophe, moreover, does not even emerge from the models, but rather from the fervid imagination of climate activists.

The following is the graph to be used as the feature image at WUWT.