Thursday, July 30, 2015

How accurate are climate model projections?

The Stockholm Resilience Center published a list of nine planetary boundaries in 2010 that is useful in understanding the current state of the global environment.  The nine include species extinction, global warming, fresh water use, land use and so on. (See THE GLOBAL ENVIRONMENT for a complete list with links to the latest research on each boundary.)

The Climate Change Boundary
Recent evidence suggests that the Earth, now passing 390 ppmv CO2 in the atmosphere, has already transgressed the planetary boundary and is approaching several Earth system thresholds. We have reached a point at which the loss of summer polar sea-ice is almost certainly irreversible. The nine planetary boundaries were developed as a project of the Stockholm Resilience Centre, founded in 2007, as a joint project of Stockholm University and the Beijer International Institute of Ecological Economics at The Royal Swedish Academy of Sciences. 

New study narrows the gap between climate models and reality

Climate models are used to estimate future global warming, and their accuracy can be checked against the actual global warming observed so far. Most comparisons suggest that the world is warming a little more slowly than the model projections indicate. Scientists have wondered whether this difference is meaningful, or just a chance fluctuation.

Dire Predictions,
Second Edition:
Understanding Climate Change

 by Michael E. Mann

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Dr Kevin Cowtan, of the Department of Chemistry at York, led an international study into this question and its findings are published in Geophysical Research Letters. The research team found that the way global temperatures were calculated in the models failed to reflect real-world measurements. The climate models use air temperature for the whole globe, whereas the real-world data used by scientists are a combination of air and sea surface temperature readings. Dr Cowtan said: "When comparing models with observations, you need to compare apples with apples.

"The team determined the effect of this mismatch in 36 different climate models. They calculated the temperature of each model earth in the same way as in the real world. A third of the difference between the models and reality disappeared, along with all of the difference before the last decade. Any remaining differences may be explained by the recent temporary fluctuation in the rate of global warming.

Dr Cowtan added: "Recent studies suggest that the so-called 'hiatus' in warming is in part due to challenges in assembling the data. I think that the divergence between models and observations may turn out to be equally fragile."

Dr Cowtan's primary field of research is X-ray crystallography and he is based in the York Structural Biology Laboratory in the University's Department of Chemistry. His interest in climate science has developed from an interest in science communication. This is his second major climate science paper. For this project, he led a diverse team of international researchers, including some of the world's top climate scientists.

Related stories:

Story Source:  Materials provided by University of York.  Kevin Cowtan, Zeke Hausfather, Ed Hawkins, Peter Jacobs, Michael E. Mann, Sonya K. Miller, Byron A. Steinman, Martin B. Stolpe, Robert G. Way. Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures. Geophysical Research Letters, 2015

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