NOAA challenged the global warming ‘pause.’ Now new research says the agency was right
By Chris Mooney
Jan 4 2017
It may have been the most controversial climate change study in years.
In the summer of 2015, a team of federal scientists at the National Oceanic and Atmospheric Administration published a blockbuster paper in Science that appeared to wipe away one of global warming doubters’ favorite arguments. The skeptics had for years suggested that following the then-record warm year of 1998 and throughout the beginning of the 21st century, global warming had slowed down or “paused.” But the 2015 paper, led by NOAA’s Thomas Karl, employed an update to the agency’s influential temperature dataset, and in particular to its record of the planet’s ocean temperatures, to suggest that really, the recent period was perfectly consistent with the much longer warming trend.
This didn’t merely surprise some scientists (who had been busily studying why global warming had appeared to moderate its rate somewhat in the early 21st century). It actually led to a congressional subpoena from Rep. Lamar Smith, chair of the House Committee on Science, who charged that “NOAA’s decision to readjust historical temperature records has broad national implications” and requested more information on why NOAA had made the dataset adjustment, including data and communications from the scientists involved.
That controversy is likely to be stirred anew in the wake of a new study, published Wednesday in Science Advances, that finds the NOAA scientists did the right thing in adjusting their dataset. In particular, the new research suggests that the NOAA scientists correctly adjusted their record of ocean temperatures in light of known biases in some observing systems — and indeed, that keepers of other top global temperature datasets should do likewise.
“We pretty robustly showed that NOAA got it right,” said study author Zeke Hausfather, a Ph.D. student at the University of California-Berkeley and a researcher with Berkeley Earth, a nonprofit consortium that has reanalyzed the Earth’s temperatures. “There was no cooking of the books, there’s no politically motivated twisting of the data.”
Hausfather completed the study with scientists based at York University in the U.K., George Mason University, and NASA, as well as an independent researcher.
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.
This highly technical switch, in turn, had the effect of increasing the overall warming of the oceans in the new dataset — and helping to wipe out claims that there’d been any recent slowdown in the rate of climate change.