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Judith Curry: The 2.8% Effect

Judith Curry, Climate Etc.

The Arctic Ocean covers about 2.8% of the total Earth’s surface area   –  The Encyclopedia of Earth

While we discuss the uncertainties in estimates of Arctic Ocean temperatures and its trends, it is useful to put into perspective its relatively small size.

The figure below was just tweeted by Ed Hawkins:


This is Figure 11.25 from the IPCC AR5 (discussed previously on Implications for climate models of their growing disagreement with observations).  Ed Hawkins has added a blue line to show Cowtan and Way’s global temperature analysis.  While Cowtan and Way is slightly warmer than HadCRUT4 for the past decade, their analysis doesn’t change the pause story very much when shown in this context.

The interesting issue is what has really been going on with the Arctic temperatures since about 2008.  In the preceding post Uncertainty in Arctic temperatures, MERRA vs the ERA-Interim showed  diverging trends after about 2007; Figure 4b of Cowtan and Way is suggestive of a steady temperature in the Arctic since 2000 (although this figure uses a 60 month running mean).

Note, comparing truly global climate model simulations with a truly global observational data set (e.g. Cowtan and Way) is better than comparing with HadCRUT4 with missing data regions.  Note, this is why Ed Hawkins previously compared (fig) the HadCRUT4 observations with climate model simulations where the missing regions were held out from the simulation data set.

So, you may be asking why we are paying such close attention to 2.8% of the globe.  It does seem surprising that this small region would have a noticeable affect on global surface temperatures, but it seems to according to Cowtan and Wray’s analysis.  In terms of the broader climate dynamics, the Arctic Ocean has an outsized influence on Northern Hemisphere climate dynamics (as per the Stadium Wave analysis).

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