Earlier this week I to reported on some of the poster sessions at the American Geophysical Meeting but was told the next day that I’m not allowed to photograph such posters to report on them. However, when the authors send me the original, for which they own the copyright, there’s nothing AGU can complain about related to me violating their photography policy.
This poster from Pat Michaels and Chip Knappenberger builds on their previous work in examining climate sensitivity differences between models and reality.
Recent climate change literature has been dominated by studies which show that the equilibrium climate sensitivity is better constrained than the latest estimates from the Intergovernmental Panel on Climate Change (IPCC) and the U.S. National Climate Assessment (NCA) and that the best estimate of the climate sensitivity is considerably lower than the climate model ensemble average.
From the recent literature, the central estimate of the equilibrium climate sensitivity is ~2°C, while the climate model average is ~3.2°C, or an equilibrium climate sensitivity that is some 40% lower than the model average.
To the extent that the recent literature produces a more accurate estimate of the equilibrium climate sensitivity than does the climate model average, it means that the projections of future climate change given by both the IPCC and NCA are, by default, some 40% too large (too rapid) and the associated (and described) impacts are gross overestimates.
A quantitative test of climate model performance can be made by comparing the range of model projections against observations of the evolution of the global average surface temperature since the mid-20th century.
Here, we perform such a comparison on a collection of 108 model runs comprising the ensemble used in the IPCC’s 5th Scientific assessment and find that the observed global average temperature evolution for trend lengths (with a few exceptions) since 1980 is less than 97.5% of the model distribution, meaning that the observed trends are significantly different from the average trend simulated by climate models.
For periods approaching 40 years in length, the observed trend lies outside of (below) the range that includes 95% of all climate model simulations.