Two Decades of Overestimated Global Warming

In a Commentary published in the Opinion and Comment section of Nature Climate Change, Fyfe et al. (2013) introduce their study of the subject by (1) stating that “global mean surface temperature over the past 20 years (1993-2012) rose at a rate of 0.14 ± 0.06°C per decade,” and by (2) noting that this warming rate was “significantly slower than that simulated by the climate models participating in Phase 5 of the Coupled Model Intercomparison Project (CMIP5).” And so it was that they went on from there to look for a reason as to why such a discrepancy should exist.

The first step of the three researchers was to compute average simulated global temperatures only at locations where corresponding observations existed – which makes a lot of sense, since a person doesn’t go looking for oranges in an apple orchard – and in doing so, they obtained “an average simulated rise in global mean surface temperature of 0.30 ± 0.02°C,” which was more than twice as great as the real-world measured rate of warming.

But wait! Fyfe et al. report that the inconsistency between observed and simulated global warming was even more striking for temperature trends computed over the past fifteen years (1998-2012), for which period they say the observed trend of 0.05 ± 0.08°C “was more than four times smaller than the average simulated trend of 0.21 ± 0.03°C.” And they also point out that the observed trend over this period, which was not significantly different from zero, actually suggested “a temporary ‘hiatus’ in global warming,” further citing the studies of Easterling and Wehner (2009) and Fyfe et al. (2011) in this regard.

And any number that is divided by zero really is infinite, which suggests that CMIP5 simulations of global warming over the period 1998-2012 could in this sense truly – but partially tongue-in-cheek – be considered to be infinitely too large, which is about as wrong as it is possible to be wrong.

Sherwood, Keith and Craig Idso

Easterling, D.R. and Wehner, M.F. 2009. Is the climate warming or cooling? Geophysical Research Letters 36: 10.1029/2009GL037810.

Fyfe, J.C., Gillett, N.P. and Zwiers, F.W. 2013. Overestimated global warming over the past 20 years. Nature Climate Change 3: 767-769.

Fyfe, J.C., Merryfield, W.J., Kharin, V., Boer, G.J., Lee, W.-S. and von Salzen, K. 2011. Skillful predictions of decadal trends in global mean surface temperature. Geophysical Research Letters 38: 10.1029/2011GL049508.


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