Based on records from satellites, there has been “no significant warming whatsoever for the last 18 years,” Cruz asserted in New Hampshire in January. That’s just one of many times he has made this claim or something close to it, which turns on looking at a particular record of the Earth’s climate — satellite readings of the atmosphere’s temperature — rather than others (such as the surface thermometer measurements that NASA and NOAA just used to declare 2015 the hottest year ever recorded).
But lately, it looks like the satellites may be getting less friendly to Cruz and his argument. Two prominent satellite datasets — one from the University of Alabama in Huntsville, and the other from Remote Sensing Systems in Santa Rosa, Calif. — both show that February of 2016 was the hottest month ever recorded in the lower troposphere, a layer of the atmosphere stretching from the surface to about 6 miles in the air.
Using the University of Alabama in Huntsville dataset, Roy Spencer, one of the scientists involved in the research, last week announced a record warm monthly measurement for the lower troposphere on his blog. And Remote Sensing Systems found the same thing, both for the lower and also the middle troposphere.
“We actually just had the hottest month ever,” said physicist Carl Mears of Remote Sensing Systems. “I really suspect that 2016 is going to be the warmest ever” out of all the years in the satellite record, he said. That record goes back to 1979.
Perhaps we shouldn’t make too much of one record warm month. But what about a new satellite dataset that also shows more warming than before?
Mears and his colleague Frank Wentz just published a new paper in the Journal of Climate, a publication of the American Meteorological Society, detailing a new correction to their satellite temperature dataset for the middle troposphere (from the surface to roughly 50,000 feet in the air). The correction was necessary because of a long-standing problem with data derived from polar orbiting satellites — as they circle the globe from top to bottom, they tend to drift.
“It might have started out its mission measuring at 2:00 in the afternoon, but years later, it’s drifted, so it’s now 6:00 in the afternoon. And most places, it’s not as warm at 6:00 as it is at 2:00,” Mears said.
Moreover, there was no way of independently checking whether the satellites were actually measuring the right temperature 8 kilometers into the atmosphere over the equator, Mears said. There are no hovering thermometers there. Previously, his team had tried to correct the problem by using a climate model to estimate that temperature, but the method was “not sufficiently accurate,” according to the new study.
So now, a new correction has been applied, and the result is that the satellite record kept by Remote Sensing Systems shows more global warming than before.
Specifically, Mears said, the prior dataset had shown about a 0.08 degree Celsius warming trend per decade for the middle troposphere, whereas the new one shows a 0.133 degree Celsius trend. Moreover, over the past 18 years that Cruz likes to cite — the period since 1998, a record warm El Nino year that officially remains the hottest year in the satellite record — there’s now also a trend, despite the fact that starting an analysis with this super-hot year tends to mute it.
“The trend, 1998 to the present, used to be slightly negative,” Mears said. “And now it’s about .06. So this adjustment I made is, it ended up having a larger effect after 1998 than it did before 1998, just because of the pattern of how the satellites drift, and that sort of thing.”
So based on Mears’ dataset, it would now appear tougher to argue that there is no warming since 1998 in the satellite record. Granted, Mears said that Remote Sensing Systems has not yet applied this correction to the data for the lower troposphere (from the surface to about 35,000 feet), an often-cited dataset.
Asked for a response to the new study, Cruz’s communications director Rachael Slobodien said, “Isn’t it convenient that alarmists keep revising data that is inconvenient? The data showed a pause, so instead of revising the theory, they revised the data.”
As this comment suggests, skeptics like Cruz still have counterarguments they can make. This new data update does not mean that the warming shown by satellites is as fast as the warming shown by ground-based thermometer and ocean surface measurements, for instance.
Nor does it mean that the warming shown by satellites matches what climate change models predict. It still lags those predictions, according to Mears. So as Slobodien’s words suggest, Cruz and his supporters can still argue that the “theory” and the “data” are misaligned.
And finally, it is important to note that the satellite researchers at the University of Alabama in Huntsville, John Christy and Roy Spencer, aren’t necessarily sold on the new correction by Remote Sensing Systems. Spencer has posted a blog post critiquing it – suggesting that it may have introduced “spurious warming.”
So Cruz could still continue to cite the Alabama dataset. Indeed, Christy explained by email that for the middle troposphere, his data still don’t show much of a warming trend since 1998. Nor do they show one for the lower troposphere, which Christy calls the “popular” dataset — and which Remote Sensing Systems has not corrected yet.
“UAH has a trend of -0.006 and current RSS is -0.014 – basically zero in both cases. 1998 was really warm in the satellite datasets,” said Christy by email, referring to measurements of the lower troposphere.
So some debates will surely continue, but the fact remains: The world is setting staggering heat records right now, including in the satellite record. And the claim that satellites don’t show any recent warming has already been widely critiqued by climate scientists as a form of cherry-picking. Now, it’s been called even more into question.
“This is definitely an advance,” said Mears. “This is how the scientific process works. You do something, you continue to evaluate it, you see something that might be wrong, and then you fix that something.”
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