Aerosol contamination in northeastern India and Bangladesh.
Credit: Wikimedia
ABERYSTWYTH: Aerosol particles in the atmosphere affect the Earth's climate in more ways than we thought, according to new research on their impact on our ecosystems.
Scientists have previously known that tiny particles suspended in the air, known as aerosols, can affect climate directly by absorbing or reflecting radiation. They can also influence the climate indirectly by seeding clouds that affect the amount of solar radiation reaching the Earth.
Now, new research published in Science today suggests that aerosols can also affect climate due to their slow impact on marine and terrestrial ecosystems, potentially affecting the amounts of carbon dioxide that enter and leave the atmosphere.
"There is a previously ignored impact of aerosols onto climate, through their impacts on the carbon cycle," said lead author Natalie Mahowald from Cornell University in Ithaca, New York. "This suggests that in the future, cleaning of aerosols due to public health concerns will make reducing carbon dioxide in the atmosphere even more difficult."
Direct and indirect effects
Aerosols are well known to have a significant influence on climate in a number of ways. The so-called 'direct' effect notes the interaction of particles with incoming solar radiation and outgoing long wave radiation.
The 'indirect' effect describes how they interact with clouds, changing their properties and seeding new clouds that prevent solar radiation from reaching the Earth. Both these absorbing and reflecting effects can result in a cooling effect on our planet below.
Mahowald suggests that aerosols have an additional climatic impact by adding nutrients to ecosystems and biogeochemical cycles, most notably the carbon cycle.
The effect occurs as aerosols supply nutrients to terrestrial and marine ecosystems, allowing the carbon-fixing organisms, such as photosynthetic plants in these systems to grow and take up additional carbon dioxide from the atmosphere.
Affecting Earth's ecosystems
Mahowald estimated the amount caused by this interaction is creating an additional, unconsidered cooling effect, by an amount comparable to that of the 'direct' aerosol effect.
"Aerosols can impact biogeochemical cycles, especially the carbon cycle (and thus carbon dioxide concentrations) by adding nutrients to different ecosystems, such as nitrogen, phosphorus or iron, or by cooling the planet and shifting precipitation," she said.
"In the atmosphere, iron is carried mostly in naturally produced aerosols, but the more soluble and bioavailable iron is also likely to be produced by combustion processes, by burning fossil fuel for example," she added. "Some marine ecosystems are iron limited, and the main way they get new iron is through atmospheric deposition. It turns out that some nitrogen fixing organisms in the ocean probably require lots of iron, and thus the iron and nitrogen cycles are linked."
