Between 2005 and 2019, the Earth absorbed enormous amounts of thermal energy. Experts speak of an “unprecedented increase” that is likely to result in unchecked significant climate changes.
The amount of energy stored in the Earth has nearly doubled in just 14 years, experts from the U.S. space and ocean agencies Nasa and NOAA report in a study in the journal Geophysical Research Letters. This intensifies the global rise in temperature, they say.
The cause is likely a mix of man-made factors and natural variability, explained Nasa researcher Norman Loeb, who led the study. Both factors probably favored warming, he said, contributing to the energy imbalance. The magnitude of the increase is “unprecedented,” he said.
Most of the heat is stored in oceans
Earth’s climate depends in part on how much heat radiation from the sun is absorbed by the atmosphere, soils and oceans, and how much is released back into space as thermal infrared radiation. “A positive energy imbalance means that the Earth system is absorbing energy, causing the planet to heat up,” Nasa writes.
For the study, experts analyzed satellite data on Earth’s thermal radiation and information from the Argo program from 2005 to 2019. As part of Argo, a fleet of robots has been recording temperature, salinity and currents in the world’s oceans, among other things, since 2000.
Because the oceans absorb almost all of the energy from the imbalance on Earth, the amounts of heat recorded by the satellites were reflected in temperature changes in the oceans. “The two independent observations agree very well,” Loeb said. That makes it clear that this is a real phenomenon, he said.
Snapshot of long-term climate change
Higher levels of greenhouse gases in the atmosphere increasingly reduce the amount of heat radiation the Earth can emit back into space. The resulting warming of the Earth, in turn, promotes ice melt and affects cloud formation, which also impacts the climate. Since 2005, the amount of greenhouse gases such as carbon dioxide (CO₂) and methane in the atmosphere has continued to increase.
At the same time, a natural weather phenomenon in the Pacific Ocean called the Pacific Decadal Oscillation (PDO) has shifted from a cooler phase to a warmer one, and the energy imbalance has continued to move toward a surplus, the researchers report. Since about 2014, the PDO has led to a reduction in cloud cover over the ocean, causing it to absorb more solar radiation, they said.
In that respect, the work is a snapshot, Loeb explained. It is not possible to predict with certainty how the Earth’s energy budget will evolve in the coming decades, he said. However, if the amount of energy absorbed by the Earth does not decrease, much greater climate changes can be expected than have already occurred.
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