Scientists are keeping tabs on the warming planet with more than one thermometer, so to speak. Ground-based sensors, ocean buoys and different types of satellite measurements have all helped show how fast the Earth is heating up.
The bad news: Global warming is still steadily proceeding. But the good news is that all of these methods broadly agree with one another, despite being collected in very different ways. That means there’s high confidence that the estimates are accurate.
Now, new research has just confirmed that yet another method matches the others.
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The findings, published yesterday in the journal Environmental Research Letters, demonstrate that temperature data collected by a satellite-based infrared measurement system are highly consistent with information gathered by sensors on the Earth’s surface.
“The estimates that we’re getting of the trends from the surface temperature network and ocean buoy network is matched to a ridiculous certainty by the trends that we’re getting from this remote sensing,” said NASA climate scientist Gavin Schmidt, a co-author on the study, which was led by fellow NASA scientist Joel Susskind.
The study focuses on a relatively recent NASA satellite measurement system known as the Atmospheric Infrared Sounder, or AIRS, that began collecting data in 2002. The system takes measurements of the Earth’s “skin temperature,” or the temperatures right at the surface of the planet.
Researchers compared this new data set to measurements taken by sensors placed directly on the surface of the Earth. They constitute a collection known as the GISTEMP data set; it includes data collected by land-based measurement stations, ships or ocean buoys, and even Antarctic weather stations.
The close agreement between the two data sets—one collected from the ground and the other from the sky—provides yet another confirmation that scientists are getting an accurate read on the progress of global warming.
Filling in the gaps
The one enduring issue with surface-based temperature measurements is that there are a few regions of the Earth where sensors are relatively sparse. These include some remote areas of Africa that lack weather stations, parts of the distant Southern Ocean and some difficult-to-access regions of the Arctic. They’re the only parts of the world where the new AIRS data seem to diverge from the surface-based measurements.
Because the discrepancies are most likely caused by a simple lack of ground-based coverage, the satellite data are likely to be most accurate for these places. The two data sets still closely agree on a global scale—but the satellite measurements may be able to fill in some important gaps in the few areas of the Earth not well-covered by surface sensors.
The Arctic is “the most interesting place that it’s mismatching,” according to Schmidt.
The AIRS data seem to show that Arctic warming may be proceeding even faster than previous estimates indicate—and scientists already believe the region to be warming about twice as fast as the rest of the world on average.
In particular, the new data suggest that warming has been highest in some specific regions of the Arctic Ocean over the last 15 years or so. According to AIRS, the Barents and Kara seas are now warming by about 2.5 degrees Celsius, or 4.5 degrees Fahrenheit, per decade.
The new data may fill in an important gap in a rapidly changing region of the world. Surface sensors in the Arctic tend to stop at the shoreline, Schmidt noted, since the sea ice makes it difficult to place data-collecting buoys in the middle of the Arctic Ocean.
These comparisons may help scientists consider new ways to produce the most accurate temperature data sets for every region of the world. Schmidt, who directs the NASA institute that produces the GISTEMP data set, noted that researchers are always thinking about ways that the surface measurements could be improved.
But since the satellite measurements and surface data otherwise complement each other so well, he said, “we may need to actually start producing blended products that use both the surface temperatures and the satellites to really say what’s going on.”
‘Nail in the coffin’
The new study may also help tackle an argument put forth by climate skeptics.
In the past, doubters of mainstream climate science have sometimes pointed to discrepancies between the satellite record and ground-based temperature measurements as evidence that scientists’ estimates of recent warming can’t be trusted.
Previously, there appeared to be some disagreements between the ground-based temperature record and a specific satellite record relying on microwave sensors—a different method than the infrared sensors examined in the new study, but still a form of remote sensing. The satellite record seemed to suggest that less warming had occurred on Earth than the surface-based temperature set showed.
But in 2017, a breakthrough paper published in the Journal of Climate suggested the satellite record required some important corrections.
When the researchers applied these corrections, the new record implied about 30% more warming than it had previously shown. That placed it in much closer agreement with the surface-based sensors.
Now, an entirely separate form of remote sensing also supports the same conclusions.
“We know the planet is warming, but this is one more nail in the coffin to people who claim that the surface temperature estimates are uncertain or not to be trusted,” Schmidt said. “This is a really good demonstration that, again, totally independent methodology ends up producing not just qualitatively the same results, but quantitatively the same results.
“And I think that’s quite impressive.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.