The climate is driven by a complicated interaction of factors. While greenhouse gases contribute to warming, other influences produce a cooling that may mask the full effects of greenhouse gases. We knew that aerosolized particulates produce a cooling effect, but it has been difficult to figure out how large this is, given the ongoing warming.

Research presented in Nature Geoscience now tries to put a number on the aerosol effect. Additional work on the same issue shows that recent changes to emissions regulations may have strongly accelerated the warming happening in the Arctic.

Aerosolized particles in the atmosphere scatter light and cool the planet by reflecting some of the Sun’s light back out into space. Additionally, these particulates may act as catalysts for the formation of clouds, allowing water droplets to accumulate around them. Clouds have a mixed impact on the climate, reflecting incoming sunlight while also insulating the planet to a degree. This particular interaction, between aerosols and clouds, remains a source of uncertainty in climate science.

Storelvmo et. al. use observational climate data from three data sets that span 1964 to 2010 to calculate how global temperature would have evolved if carbon dioxide emissions had remained at 1964 values. Their analysis shows that the cooling effects of aerosols masked approximately one-third of the global warming that is attributable to increased greenhouse gas concentrations; this masking effect is strongest before 1990.

Though global climate change is affecting the whole planet, the Arctic has seen accelerated warming compared to the rest of the planet. The reasons for this amplified Arctic warming are still not completely clear. A paper published by Navarro et. al. in the same issue of Nature Geoscience suggests that it, too, comes down to aerosols. The paper uses climate models to show that European emissions regulations, which reduced the output of aerosol particulates starting in 1980, may have inadvertently contributed considerably to Arctic warming by reducing the aerosol cooling effect.

Navarro et. al. simulate the global climate using the Norwegian Earth System Model to study this phenomenon. Their investigations incorporate sulfate-based aerosols by including the real emissions reductions that occurred in Europe between 1980 and 2005, comparing that to a scenario where those emissions reductions had not occurred (it fixes emissions at the 1980 levels).

The results show that an average of half the Arctic warming during this period may be explained by the reduction in emissions from Europe, which reduced aerosolized sulfates and their cooling effects. In other words, an action taken to protect the environment may have actually ended up causing some harm. The results are surprising because aerosolized sulfur particles typically do not last long in the atmosphere, so it was expected that the effects of these particles would be primarily localized to the area producing the emissions.

Taken together, these two articles demonstrate the profound effects of human emissions on the environment. The degree to which aerosol particulates can mask greenhouse warming has been unclear and may have been underestimated due to uncertainty about the effect of clouds. These papers suggest the impact has been significant and that, as we clean up aerosols, we may also be enhancing future warming.

Nature Geoscience, 2016. DOIs: 10.1038/NGEO2670, 10.1038/NGEO2673. (About DOIs).