Small things can have big consequences. Take the plant plankton that populate Earth's oceans. When zooplankton eat them, the phytoplankton release a chemical called dimethyl sulfide (DMS), and it is this that people refer to when they talk about the “smell of the sea”. Chemical reactions in the atmosphere turn DMS into sulfur-containing particles that provide a surface on which water vapor can condense. Do that often enough and the result is a cloud that in turn affects both the local weather and, by reflecting sunlight into space, the Earth's climate.
Other little things have similarly extensive effects. Sulfur from ship funnels also creates particles that seed clouds, creating series of puffy white “ship tracks” seen in satellite images. Soot from fossil fuel combustion, meanwhile, has the opposite effect. It is made of dark particles that absorb solar radiation. energy, which warms the air around them and discourages cloud formation. If sulfur particles reach high enough in the atmosphere (perhaps thanks to a volcanic eruption), they can form a haze that blocks some sunlight from reaching the Earth's surface.
But while scientists know in general terms how these processes work, quantifying them is much more difficult. Uncertainties about the behavior of 'aerosols', as various small particles in the air are collectively known, are one of the main sources of scientific uncertainty in climate models. They are therefore a major reason for the error bars around projections of how hot the Earth is. will be for a certain increase in the amount of carbon dioxide in the atmosphere.
Climate scientists hope that NASA's new satellite, PACE (for “Plankton, Aerosol, Cloud, ocean Ecosystem”), which was launched into orbit on February 8, will reduce uncertainties surrounding aerosols. PACE's cameras will sweep the planet every one to two times. days to create a continuously updated count of the very small things floating in the oceans (plankton) and the air (aerosols).
PACE's main camera is sensitive to the light spectrum between ultraviolet and near-infrared. For the oceans, this means that PACE can distinguish different types of phytoplankton. “That's powerful because diatoms feed fisheries [and] Cyanobacteria can be harmful,” said Jeremy Werdell, NASA oceanographer and PACE chief scientist. Two other instruments mounted on PACE will provide information on the size and shape of aerosols, making it possible for the first time to distinguish soot from sea spray. and particles produced by the combustion of fossil fuels.
That could be “transformative” for climate models, says Gavin Schmidt, a climate scientist who also works at NASA. Modelers have had to compensate for the limited nature of existing aerosol data with informed guesswork. As a result, different climate models vary considerably in their estimates of how powerfully aerosols affect the climate.
Such uncertainties affect questions about how air pollution affects climate change. Laws in Europe and North America have reduced the amount of air pollution from fossil fuels since the 1980s. This is a boon to human health. But it has also lifted a veil of smog that masked some of the warming caused by greenhouse gas emissions. Cleaning up air pollution could be one of the most important influences on the climate in the coming decades. Better data will enable better models.
Similarly, climatologists are divided over the effect of rules adopted by the International Maritime Organization, part of the United Nations, which restricted the amount of sulfur in marine fuel as of January 2020. Some believe that the reduction of sulfur in ship exhaust may have contributed to the exceptionally high temperatures recorded around the world in 2023. Others think the effect was minimal.
There are many more questions that climatologists would like answered. On the whiteboard in Kirk Knobelspiesse's office at NASA's Goddard Space Flight Center in Greenbelt, Maryland, is a list of 18 projects. It ranges from collecting live data on volcanoes and forest fires to answering what happens when soot from agricultural fires that burn annually in West Africa lands on the tops of sea clouds, darkening the face they form in front of the sun. The answers to all these questions depend on the behavior of little things. After decades of uncertainty, answers may be coming.
© 2024, The Economist Newspaper Ltd. All rights reserved.
From The Economist, published under license. Original content can be found at www.economist.com
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Published: May 7, 2024 8:00 PM IST