In their paper, Karl's team sums up the combined effect of additional land temperature stations, corrected commercial ship temperature data, and corrected ship-to-buoy calibrations. The group estimates that the world warmed at a rate of 0.086°C per decade between 1998 and 2012—more than twice the IPCC's estimate of about 0.039°C per decade. The new estimate, the researchers note, is much closer to the rate of 0.113°C per decade estimated for 1950 to 1999. And for the period from 2000 to 2014, the new analysis suggests a warming rate of 0.116°C per decade—slightly higher than the 20th century rate. “What you see is that the slowdown just goes away,” Karl says.

And that's without including the elephant in the room: Arctic warming. A 2014 paper in the Quarterly Journal of the Royal Meteorological Society highlighted how the scarcity of temperature data from the Arctic, which is warming twice as fast as the rest of the planet, has produced a significant “cool” bias in the global trends, especially since 1997.

“The post-1998 period is really difficult, partially because of Arctic warming and partly because of the change in SST measurements,” says Kevin Cowtan, a computational scientist at the University of York in the United Kingdom, who co-authored the 2014 paper. “The fact that it's caused problems is completely understandable, if unfortunate.”

Why is noaa turning down many of the arctic sensors when that is an area of most concern?

Therefore, our estimate of the additional warming over recent decades in the arctic, not included in our primary global analysis, is likely to be an underestimate of the actual warming. However, because our data date back to 1880, further investigation (beyond the scope of this analysis) is required to demonstrate the optimum interpolation approach for both short and long periods in data-sparse, high-latitude regions.