They fiddled with the surface sea temperature record to make it say what they wanted. The data didn't say what they wanted so they adjusted it!
To understand the new study — which gets complicated fast, as it dances back and forth between different datasets — you first need to understand the biggest issue underlying the original NOAA analysis. This involved reconciling the data from two separate ways of measuring temperatures at or near the surface of the planet’s oceans (which are the largest component of determining its overall temperature).
One data source was global ships, which draw in ocean water in their engine rooms and take its temperature. Key parts of the past ocean temperature record are based on these reports. The other data source is buoys, which float in the water, take measurements, and relay the results to satellites. In general, buoys have been relied upon more for measurements beginning in the 1990s, as they have become more widely deployed. They are, naturally, a more direct measurement, one less mediated by physical ships and fallible humans.
But the increasing use of buoys created an issue of reconciling the two data sources to piece together a seamless and continuous record — and NOAA was, essentially, siding with the buoys when it comes to accuracy. “The ship data are systematically warmer than the buoy data,” NOAA explained in the controversial study. (After all, ship engines are relatively warm places.) It also said that the buoy data are “more accurate and reliable.”
Failing to account for this difference, once the shift from ship data to buoy data occurred, had led NOAA’s temperature record to be too cold — and also appeared to dampen the overall rate of global warming. So to better patch together a long term temperature record necessarily reliant on both data sources, NOAA used a “bias correction” to take this into account, and more generally gave greater weight to the buoy data, in updating its dataset.
The old ship data was "too warm" so they adjusted it downward just like they've done with land temperatures. Policy driven science.
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