Satellites may have underestimated global warming for decades

Every day we receive news about climate change on the planet or related problems. It’s rising ocean levels, rising temperatures and imbalances in ecosystems – to name a few. The most recent is that the global warming that has already occurred may have been even worse than previously thought: a new study has found that satellite measurements likely underestimated the warming of the lowest levels of the atmosphere (the troposphere) over the past 40 years.

“Satellite measurements of the troposphere have either underestimated its temperature or overestimated its humidity,” said study leader Ben Santer, climate scientist at the Lawrence Livermore National Laboratory – LLNL, Calif., in a statement published May 20 in the Journal of Climate.

Tropical water vapor highlighted in red in NASA image.Source:  NASA/Reproduction

Santer’s team compared four different proportions of climatic properties: the ratio of tropical sea surface temperature to tropical water vapor; the ratio of the temperature of the lower troposphere to tropical water vapor; the ratio of middle and upper troposphere temperature to tropical water vapor; and the relationship between the average and high temperature of the troposphere with the temperature of the tropical sea surface.

In the models used to measure global warming, these proportions are strictly defined based on the physical laws that govern moisture and heat: it takes more energy to heat moist air than dry air, because water efficiently sucks heat ; Warmer air can also retain more moisture than cooler air – a phenomenon that is visible in morning dew: as the air cools during the night, it spills water.

Study conclusions

The study concluded that although basic physical equations govern the relationship between air temperature and humidity, many measurements of temperature and humidity used in climate models diverge from this relationship. “Currently it is difficult to determine which interpretation is more reliable,” said Santer.

For the scientist, the analysis reveals that several sets of observational data seem to be at odds with other complementary variables – those that are physically related to each other – that are measured independently. The main discrepancies found are in the data with the lowest ocean and tropospheric surface warming values, which leads the team to believe that measurements showing the least warming may also be less reliable.

Study verified ocean temperature.Study verified ocean temperature.Source:  Freepik

But the researchers found that satellite observations didn’t follow supposedly well-defined rules — they fell over a wide range, depending on which dataset was used. This may mean that datasets that better fit the physical rules governing humidity and heat are more accurate than others.

The datasets that best follow the rules for water vapor rates and temperature tend to be those that show the greatest warming of the sea surface and the troposphere, the researchers found. Likewise, the models that best followed the rules for mean and high tropospheric temperatures and sea surface temperature ratios were those with the highest measurements of sea surface temperature.

It is not yet possible to believe that the satellites are making mistakes – more studies need to be done. But using the models to test real-world observations could help researchers track historical warming more accurately, according to study co-author Stephen Po-Chedley, an atmospheric scientist at LLNL. “These comparisons between complementary measurements can shed light on the credibility of different datasets,” the researcher said.

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