New studies increase confidence in NASA's measurement of Earth's temperature

A new evaluation of NASA's global temperature data revealed that the agency's estimates of the Earth's long-term temperature rise over the last few decades are accurate at less than 30 percent. one-tenth of a degree Fahrenheit, which suggests that past and future research accurately captures surface temperatures.

The most comprehensive evaluation of the statistical uncertainty in the GISSTEMP data product shows that annual values ​​are probably accurate to 0.09 degrees Celsius in recent decades and 0 27 degrees Fahrenheit (0.15 degrees C). at the beginning of the record almost 140 years.

This database, maintained by NASA's Goddard Institute for Space Studies (GISS) in New York, is one of the few scientific institutions in the world to monitor the Earth's temperature and its increase in recent decades. This record of global temperature has provided one of the most direct landmarks on how the climate of our home planet has changed with increasing greenhouse gas concentrations.

The study also confirms what researchers have been saying for some time now: The increase in Earth's temperature since 1880 – about 2 degrees Fahrenheit or a little over 1 degree Celsius – can not be explained by any uncertainty or error in the data. In the future, this assessment will give scientists the tools they need to explain their results with greater confidence.

GISTEMP is a widely used index of anomaly of the average temperature of the planet's surface. It indicates how much the temperature of the Earth is warmer or cooler than normal in a given year. "Normal" is defined as the average over a base period from 1951 to 1980.

NASA uses GISTEMP in its annual global temperature update, in partnership with the National Oceanic and Atmospheric Administration. (In 2019, NASA and NOAA concluded that 2018 was the fourth hottest year ever, with 2016 in first place.) The index includes surface temperature data from land and sea ascending to 1880 and today incorporates measurements from 6,300 weather stations. stations, ships and buoys around the world.

Previously, GISTEMP provided an estimate of uncertainty taking into account spatial differences between weather stations. As with other surface temperature records, GISTEMP estimates temperatures between weather stations using data from the nearest stations, a process called interpolation. The quantification of the statistical uncertainty present in these estimates helped the researchers to be sure that the interpolation was accurate.

"It's important to understand uncertainty because we know that in the real world, we do not know everything perfectly," said Gavin Schmidt, director of GISS and co-author of the study. "All science is based on knowing the boundaries of the numbers you are proposing, and these uncertainties can determine whether what you see is a change or a really significant change."

The study revealed that individual and systematic changes in temperature measurement over time were the most important source of uncertainty. The degree of coverage of the weather stations also contributed. The interpolation of data between the stations has created some uncertainty, as has the process of normalizing data collected with different methods at different times in history.

After adding these components, the uncertainty value of GISTEMP in recent years was still less than one-tenth of a degree Fahrenheit, which is "very small," Schmidt said.

The team used the updated model to reaffirm that 2016 was most likely the hottest year in history, with a probability of 86.2%. The next most likely candidate for the hottest year ever recorded was 2017, with a probability of 12.5%.

"We made the quantization of uncertainty more rigorous, and the conclusion of the study was that we could trust the accuracy of our global temperature series," said L & # 39; lead author, Nathan Lenssen, Ph.D. student at Columbia University. "We do not have to rephrase the conclusions based on this analysis."

Another recent study assessed GISTEMP in a different way, which also boosted confidence in its estimate of long-term warming. An article published in March 2019, led by Joel Susskind of NASA's Goddard Space Flight Center, compared GISTEMP data with that of the Atmospheric Infrared Sounder (AIRS), which is embedded on NASA's Aqua satellite.

GISTEMP uses recorded air temperature with thermometers slightly above ground or sea, while AIRS uses infrared detection to measure the temperature at the Earth's surface (or "temperature of the earth"). skin ") from the space. The AIRS record of the temperature change since 2003 (which begins when Aqua is launched) closely matches the GISTEMP record.

The comparison of two similar measurements but recorded in very different ways made it possible to ensure that they were independent of each other, Schmidt said. One of the differences was that the AIRS system showed more warming in the northern latitudes.

"The Arctic is one of the places where we had already detected the warmest hottest .The AIRS data suggest that it is heating up even faster than expected," said Schmidt, co-author from the Susskind newspaper.

Together, the two studies helped establish GISTEMP as a reliable index for current and future climate research.

"Each of these solutions is a way of trying to prove that what you are doing is real," Schmidt said. "We are testing the robustness of the method itself, the robustness of the assumptions and the end result against a completely independent dataset."

In any case, he said, the resulting trends are more robust than can be explained by uncertainty in the data or methods.

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