As the pace of warming has shot up, politicians have responded in part by casting doubt on the global temperature data. They've argued that we should ignore surface data sets and pay attention to satellite measurements of the upper atmosphere, which just happen to show a little less warming in recent years. The work that goes into maintaining all of these data sets is pretty complex—enough so that we recently dedicated about 5,000 words to the subject.

One of the people we talked to for that story was Carl Mears , who helps run one of the major satellite data sets of upper air temperatures. Mears explained the calibrations and corrections that go into that data set and frankly discussed the uncertainties surrounding it. Overall, he felt that the uncertainties of the satellites' data were greater than those for surface data sets like those run by NASA and the UK Met Office.

Building on analysis of that uncertainty, Mears and his colleague Frank Wentz have published a paper describing an update to their data set—one that ends up increasing the warming trend significantly.

The biggest source of error in the satellite measurements is that the satellites can’t maintain a clockwork orbit forever. Over the years, the time of day that they pass over your house (for example) gradually drifts. So even in a Groundhog Day scenario where every day’s weather is identical, the satellites could measure a change in temperature over time simply because they are making measurements later and later in the day.

It’s a very difficult problem to adjust for. Mears and the Remote Sensing Systems (RSS) crew have been using a climate model to estimate the impact of this time-of-day drift on the satellite measurements. But they were under no illusions that this provided a perfected correction. The new update resulted from looking for improvements.

They started by testing three very different methods. Working with the second generation of these satellites, which started coming online in 1999, they first excluded all the measurements made by satellites going through the part of their life where the time-of-day drift was greatest. They then tried using the two satellites that successfully maintained rock-steady orbits using thrusters as references to adjust the others. Finally, they applied a tweaked version of their climate model adjustment.

All three techniques had pretty similar results, giving the researchers confidence that they were on the right track. Only the climate model adjustment can work with the first-generation satellites, though, so that’s the one they’re using in this new version of their data set. The new work does a little better job of effectively applying the patterns from the climate model to the actual measurements.

The new version of their mid-troposphere record, which is meant to represent temperatures about 5 kilometers above the surface, now shows a stronger warming trend. From the start of the record in 1979 through 2014, the warming trend increases from 0.078 °C per decade to 0.125 °C per decade. (For comparison, surface data sets show trends closer to 0.16 °C per decade.) The researchers have yet to update their lower troposphere record. That has shown more warming than its mid-troposphere counterpart, and its trend will likely increase as well.

For one test of the updated record, the researchers compared it to satellite measurements of water vapor they also maintain. Over the tropics, warm, moist air from the surface rises strongly, such that the amount of atmospheric water vapor should be very closely tied to temperature. The updated record fit pretty closely, as did another satellite dataset run by the National Oceanic and Atmospheric Administration. The University of Alabama in Huntsville record, which is run by prominent climate “skeptics” John Christy and Roy Spencer, stood out as a much poorer fit. However, a pending update to that record looks like it will bring it a little closer to the rest of the pack.

In either version of either data set, February has set a new record for warmest month in the satellite record. As expected, the warmth of the El Niño in the tropical Pacific helped 2015 smash the surface temperature records and is now showing up in the upper atmosphere records. That spells trouble for those who have tried to (incorrectly) use the El-Niño boosted peak of 1998 to argue that satellite records currently show no warming.

In a commentary piece just last week, Congressman Lamar Smith (R-Texas), who has subpoenaed e-mails from NOAA scientists and accused them of manipulating their data to inflate recent warming, repeated his sentiment that satellite records are the gold standard. “Atmospheric satellite data, considered by many to be the most reliable, has clearly showed no warming for the past two decades,” he wrote, “This fact is well documented, but it does not fit the liberal politics of the administration or the national media.”

We’ll have to see if that rhetoric changes now.

Journal of Climate, 2016. DOI: 10.1175/JCLID-15-0744.1 (About DOIs).