During this time, Smith falsely represented the research on the topic. He said climate data had “clearly showed no warming for the past two decades,” which is not true. And when a new paper arguing for a slowdown during a different time period came out last year in Science, Smith said that it “confirms the halt in global warming.”
But that paper showed no halt—it only argued for the slowdown. And its authors specifically wrote: “We do not believe that warming has ceased.” There is no valid scientific debate about a “halt,” but Smith seemed to be trying to manufacture one.
The Center for Science and Democracy, a nonpartisan advocacy group for scientists in the civil service, said that Smith was harassing NOAA for doing its job. “The use of a sledgehammer of a congressional subpoena to cast so wide a net is unprecedented and unjustified,” said Andrew Rosenberg, its director, in a letter to the House committee.
In June of this year, Smith responded by issuing a subpoena to the Center’s parent organization, the Union of Concerned Scientists. The non-profit said that Smith was well outside his legal authority, and it declined to respond.
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Which brings us back to the new study. It finds that Smith was wrong: NOAA’s results are scientifically defensible, and its global temperature records match those prepared by different means. It does this by comparing NOAA’s record to all the smaller, highly reliable records that constitute it.
“The way that NOAA makes an ocean record is they take data from a lot of different sources, and they smush it all together into a single record. They do this so they can have a long, continuous record back to 1880 or so,” Hausfather told me.
Creating a record from 1880 is difficult, however—especially for the oceans, where there are no long-standing weather stations. Scientists have to piece disparate historical records together over time. This is a typical problem in climate science, but it’s typical that some of those constituent datasets impose slightly different biases on the data.
Before the 1990s, most of NOAA’s ocean-temperature records came from ships logs. Ships are tricky because they have historically measured the sea surface in different ways. During the mid-20th century, most sailors measured the water temperature using “bucket measurements”: They hauled a bucket over the side, dipped it in the water, brought it up, and put a thermometer in it.
More recently, most ships measure the ocean temperature mechanically through an “engine-intake valve.” Ships pump water into their hull in order to cool the engine room, and a thermometer measures its temperature on the way. This can introduce bias to the numbers, though: Because engine rooms get hot, engine-intake-valve readings are skewed warmer than the actual ocean.
That’s partly why, since the 1990s, the governments of the world have deployed a fleet of new sensors to measure the changing sea. Buoys, satellites, and autonomous sensors called Argo floats all patrol the ocean and measure its conditions. This has dramatically changed the makeup of NOAA’s temperature record: Whereas 95 percent of NOAA’s readings came from ship engine rooms in the early 1990s, 85 percent now come from buoys.