Much has been made of the supposed pause in global warming for the last 15 years or so on the part of those who deny that there is warming, or that people aren’t responsible or that it’s good for us or whatever argument they think might sound best in a given situation. RealClimate, a site run by climatologists, informs us that a new analysis of data from that time frame that uses satellite data to fill in gaps in areas of the Arctic, a part of the world warming significantly faster than most others, that don’t have ground stations. As Stefan Rahmstorf explains:
The “Arctic hole” is the main reason for the difference between the NASA GISS data and the other two data sets of near-surface temperature, HadCRUT and NOAA. I have always preferred the GISS data because NASA fills the data gaps by interpolation from the edges, which is certainly better than not filling them at all.
I won’t go into the details of what they did since you can read it here but the results were surprising even to the scientists involved and a short summary from RealClimate is as follows:
The surprising result
Cowtan and Way apply their method to the HadCRUT4 data, which are state-of-the-art except for their treatment of data gaps. For 1997-2012 these data show a relatively small warming trend of only 0.05 °C per decade – which has often been misleadingly called a “warming pause”. The new IPCC report writes:
Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends. As one example, the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to +0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade).
But after filling the data gaps this trend is 0.12 °C per decade and thus exactly equal to the long-term trend mentioned by the IPCC.
If this study gets any attention in the media the accusations of fakery will start to fly soon after.