Earth's surface heating up, NASA study confirms

Satellite measurements by NASA researchers have verified the ground-based data which shows the Earth's surface has been warming globally over the past 15 years.

The team used measurements of the 'skin' temperature of the Earth taken by a satellite-based infrared measurement system called AIRS (Atmospheric Infra-Red Sounder) from 2003 to 2017.

The researchers compared these with station-based analyses of surface air temperature anomalies -- principally the Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP).

The study, published in the journal Environmental Research Letters, found a high level of consistency between the two datasets over the past 15 years.

"AIRS data complement GISTEMP because they are at a higher spatial resolution than GISTEMP, and have more complete global coverage," said Joel Susskind, from NASA's Goddard Space Flight Center in the US.

"Both data sets demonstrate the Earth's surface has been warming globally over this period, and that 2016, 2017, and 2015 have been the warmest years in the instrumental record, in that order," Susskind said in a statement.

"This is important because of the intense interest in the detail of how estimates of global and regional temperature change are constructed from surface temperature data, and how known imperfections in the raw data are handled," he said.

AIRS data reflects skin temperature at the surface of the ocean, land and snow/ice covered regions.

Surface-based data are a blend of two metre surface air data anomalies over land, and bulk sea surface temperature anomalies in the ocean.

To compare the two, the researchers constructed monthly grid point climatologies for each calendar month and for each set of data, by averaging the monthly values over 2003 to 2017.

"Interestingly, our findings revealed that the surface-based data sets may be underestimating the temperature changes in the Arctic," said Gavin Schmidt, from NASA's Goddard Institute for Space Studies.

"This means the warming taking place at the poles may be happening more quickly than previously thought," Schmidt said.