March 6, 2014

expert reaction to new report on climate sensitivity published by the Global Warming Policy Foundation

A report published by the Global Warming Policy Foundation (GWPF) argued that observational evidence indicates the climate is less sensitive to greenhouse gases than climate models estimate.

Dr Ed Hawkins, Senior research scientist at the National Centre for Atmospheric Science and University of Reading, said:

“This lengthy report highlights an important area of climate science for predicting what average global temperatures will be – but it does not actually tell us anything new. 

“Despite criticising current and past IPCC methodology, the report’s conclusions on the amount of expected warming over the coming few decades are broadly in line with the mainstream scientific consensus.  Remarkably for a report published by the GWPF, the authors agree with mainstream climate scientists that significant further warming is expected.  For example, they expect to see an additional 2.1C warming in the next 80 years, on top of the 0.8C warming already seen, under a business-as-usual emissions scenario. 

“If we broadly agree on this, the debate can crucially move on to what action is needed to deal with a warming planet.”

Prof Myles Allen, Head of the Climate Dynamics Group at the University of Oxford, said:

“What is most interesting about this report is Lewis and Crok’s best estimate of the Transient Climate Response (TCR), which is the property of the climate system that determines how much warming we should expect over the coming century under any given emissions scenario.  Their prediction of 1.35 degrees C is, even if correct, only 25% lower than the average of the general circulation models used in the IPCC 5th Assessment.  A 25% reduction in TCR means the warming we might have expected by 2050 might take until the early 2060s instead.  Their 5-95% range of uncertainty in TCR (kindly provided by Nic Lewis) is 0.9-2.5 degrees C, almost exactly in line with the range of the models shown in their figure (1.1-2.6 degrees C).

“That said, there are reasons to believe that the empirical estimates of TCR provided in the Otto et al (2013) study from which the GWPF report draws heavily (and on which I was a co-author) may be biased too low by incomplete data coverage.  So the actual discrepancy with CMIP-5 may be even smaller.  That’s one of the many reasons the IPCC relies on a range of sources to inform key conclusions and not just a single study or approach.”

Prof Rowan Sutton, National Centre for Atmospheric Science and University of Reading, said:

“This report describes one approach amongst many for estimating the magnitude of future climate change.  It argues for a best estimate of the Transient Climate Response (TCR) of 1.35 degrees C, which is well within the likely range of 1-2.5 degrees C provided in the AR5.  It is also only a little below the average of the AR5 models.  This small difference would delay warming a bit but doesn’t alter our basic understanding of climate change.

“This report is a perfect example of why the IPCC process, based on large author teams, a full assessment of all the peer reviewed literature, and multiple rounds of review, is needed.  If climate change turns out to be at the lower end of the IPCC range, it will be good news; but even this report projects that under a high emissions scenario a warming of 2.9 degrees C should be expected by 2081-2100, well above the 2 degree target that is the focus of international policy discussions.  Substantial additional warming would also occur after 2100.”

Prof Jonathan Gregory, National Centre for Atmospheric Science, University of Reading and Met Office Hadley Centre, comments:

“Although the approach used claims to use an ‘observational’ estimate of TCR, all estimates rely on some form of simple or complex climate model, and all methods have weaknesses, as discussed in the AR5.

“Furthermore, our own work at the University of Reading has shown that the method they use to make projections consistently leads to underestimates of future temperature change.  This is especially true for low emissions scenarios.”

¹ the Transient Climate Response, or TCR, is an important measure of the climate’s sensitivity to greenhouse gas increases.

Dr Chris Huntingford from the Centre for Ecology and Hydrology said:

“One persistent frustration is this belief that climate research is undertaken without any attention paid to the economic consequences of major emissions reductions.  We are all acutely aware that to keep global warming constrained to two-degrees since pre-industrial times will most likely need a major alteration to energy policy.  This is even for lower climate sensitivities.  We definitely do worry about what reductions are possible and without causing financial damage.

“Socio-economists already collaborate with climate researchers, but this needs to be taken much further.  If only those of incredibly sharp economic understanding and who contribute to the Global Warming Policy Foundation would, instead of continuously attacking efforts by the climate modelling community, collaborate with us.  Much progress could then occur.  They could tell us precisely what reductions in emissions they believe to be feasible, from which we can then calculate climate implications based on the remaining emissions.  These calculations would include the factoring in of the, and we’ve always agreed large, climate sensitivity uncertainty.”