Researchers analyzed nearly twenty years of satellite observations together with modern atmospheric reanalysis to assess how aerosols—tiny particles from pollution, wildfires and volcanic eruptions—affect clouds and Earth's energy balance. They report a clear hemispheric "balancing act": opposite aerosol trends in the two hemispheres produced contrary effects on reflected sunlight.
In the Northern Hemisphere, cleaner air above industrial regions reduced particles that help clouds reflect sunlight, so more solar energy reached the surface. In the Southern Hemisphere, large increases in natural aerosols after events such as the 2019–2020 Australian wildfires and the 2022 Hunga Tonga–Hunga Ha'apai eruption made clouds brighter and sent more sunlight back to space. Because these changes work in opposite directions, they largely cancel on a global scale.
The authors conclude that aerosols had little net global influence on the recent rise in Earth’s heat imbalance. From 2003 to 2023, Earth gained heat at a rate of about half a watt more energy per square meter each decade, and the increase was driven mainly by changes in reflected sunlight rather than by changes in heat escaping to space. Two independent methods—satellite observations and reanalysis estimates of sulfate particles—showed the same hemispheric pattern.
The lead author, Chanyoung Park, and coauthor Brian Soden note that understanding this hemispheric pattern helps focus attention on other drivers of warming, such as changes in cloud behavior linked to surface warming and natural climate variability. The study appears in Science Advances and was funded by NOAA’s Climate Program Office program and NASA. Source: University of Miami.
Difficult words
- aerosol — Very small particles in air from various sources.aerosols
- reanalysis — A modern dataset combining observations and models.
- hemispheric — Relating to one half of the Earth.
- reflect — Send light back from a surface or object.reflected
- sulfate — A chemical particle found in air pollution.
- imbalance — A situation with unequal amounts, not balanced.
- satellite observation — Measurements of Earth made from instruments in space.satellite observations
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Discussion questions
- How does the hemispheric balancing of aerosol effects make it harder to identify causes of global warming? Give reasons from the article.
- What might be the policy implications of the finding that Northern and Southern Hemisphere aerosol trends largely cancel globally?
- The authors mention cloud behavior and natural climate variability as other drivers. How could researchers investigate which of these influences future warming more?
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