When Pro-AGW Studies Disagree on Timing and Methodology

Two recent studies are at odds over when human-altered climate will emerge from historic variation, Mora et al, and Hawkins et al.

A few essential diagrams from the studies (apologies for the rough fit within my blog's layout, but further minimization would have resulted in text that's impossible to read)...

Mora et al, Figure 1:


Mora et al, Figure 2:


Hawkins et al, Figure 1:


These images pack a lot of info into a small area, not unlike the studies themselves, so let me briefly summarize.

Maybe I should first explain some abbreviations. RCP45 is one Representative Concentration Pathway, or greenhouse gas prediction, used in the latest IPCC Assessment Report (AR5). Here's an image which might better elaborate.



Both papers use the RCP45 projection in their research.

Hawkins et al lists the specific climate models used in abbreviated form (CSIRO Mk3.6 GCM, HadGEM2-ES, NorESM1-M, etc.) in the upper right of Fig. 1a, whereas Mora et al mentions the general use of CMIP5 models, while only singling out GFDL-ESM2G, as far as I can tell.

The authors of Hawkins et al believe the methodology of Mora et al is flawed, leading to an early man-made signal emergence from natural variability. Seems like a damning accusation, right? Something deniers could howl and rage over, and use as evidence that climate modeling is bogus or useless, or both, one might assume. But it's not the case, really, when you step back and look at the larger picture and how they both agree. Notice that each paper clearly agrees that climate will eventually emerge from background thanks to human emissions, and that it will happen on average soonest in the tropics, but have the greatest temperature anomaly at the poles. In other words, the papers agree to a large degree on several aspects of climate change, and with IPCC AR5 findings.

They merely disagree over timing of the emergence. It's a classic case of scientists arguing amongst themselves in order to expand the limits and specifics of our knowledge, and, while this frontier debate will continue and may have serious implications for policy and adaptation, it has little or no impact on the viability of climate models or the well-established reality of man-made climate change in general. Claiming otherwise is standard denier ignorance and tosh.

Thanks to contributor tokodave over at Phil Plait's Bad Astronomy blog for bringing these interesting studies to my attention.