The new study uses satellite data in the southern hemisphere to understand the global composition of clouds during the Industrial Revolution. This research addresses one of the biggest uncertainties in current climate models ̵1; the long-term effects of small atmospheric particles on climate change.
Climate models currently include the impact of greenhouse gases on global warming as well as the cooling effects of atmospheric aerosols. The small particles that make up these aerosols are produced by human sources, such as emissions from cars and industry, as well as from natural sources, such as phytoplankton and sea spray.
They can directly affect the flow of sunlight and heat in the Earth’s atmosphere and also interact with clouds. One way they do this is to strengthen the ability of clouds to reflect sunlight back into space by increasing the concentration of droplets. This in turn cools the planet. The amount of sunlight reflected in the universe refers to the earth’s albedo.
However, there is a very limited understanding of how aerosol concentrations have changed between early industrial times and the present. This lack of information limits the ability of climate models to accurately estimate the long-term effects of aerosols on global temperatures – and what impact they could have in the future.
Now an international study conducted by the universities of Leeds and Washington has recognized that remote, untouched parts of the southern hemisphere provide an overview of what the early industrial atmosphere looked like.
The team used satellite measurements of the concentration of cloud droplets in the atmosphere in the northern hemisphere – heavily polluted by today’s industrial aerosols – and over the relatively untouched southern ocean.
They used these measurements to quantify possible changes caused by industrial aerosols in the Earth’s Albed since 1850.
Results published today in the magazine PNAS, suggest that initial aerosol concentrations and cloud droplet numbers were much higher than currently estimated in many global climate models. This could mean that man-made atmospheric aerosols do not have as strong a cooling effect as some climate models estimate. The study suggests that the effect is likely to be milder.
Co-investigator Daniel McCoy, a researcher at the School of Earth and the Environment in Leeds, said: “The limitations of our ability to measure aerosols in an early industrial atmosphere have made it difficult to reduce uncertainty about how much warming there will be. in the 21st century.
“Ice cores have provided millennium carbon dioxide concentrations in the past, but aerosols do not linger in the same way. One way we can try to look back in time is to explore a part of the atmosphere that we have not polluted. yet.
“These remote areas allow us to look into our past, and that helps us understand climate records and improve our predictions about what will happen in the future.”
Co-author Isabel McCoy of the Atmospheric Sciences Department in Washington said: “One of the biggest surprises for us was how high the concentration of cloud drops in the clouds of the Southern Ocean. The way in which the concentration of cloud droplets increases in the summer says that marine biology plays an important role in determining the brightness of clouds in unpolluted oceans now and in the past.
“We see high concentrations of cloud droplets when observed by satellites and aircraft, but not in climate models. This suggests that gaps in the mechanisms of aerosol-cloud interaction and mechanisms of aerosol production in an intact environment are shown in the model.
“By continuing to observe the pristine environment through satellites, aircraft and ground platforms, we can improve the representation of complex mechanisms that control cloud brightness in climate models and increase the accuracy of our climate forecasts.”
Co-author Leighton Regayre, a researcher at the School of Earth and the Environment in Leeds, said: “Science supporting our climate models is constantly improving. These models address some of the most pressing and complex environmental issues of modern times, and climate scientists have always been at the forefront of the fact that there are ambiguities.
“We only get the answers we need to fight global warming through regular science inquiries. Our team used millions of variants of the model to examine all potential uncertainties, which is equivalent to a clinical trial with millions of participants.
“We hope that our findings, together with studies on the detailed process of aerosol production and aerosol-cloud interactions in a pristine environment that have motivated our work, will help guide the development of the next generation of climate models.”
Paper “Hemispherical contrast in cloud microphysical properties reduces the need for aerosol enforcement” PNAS, 27 July 2020.
Fire aerosols reduce the productivity of the global terrestrial ecosystem through climate change
Isabel L. McCoy et al., “Hemispheric Contrast in Cloud Microphysical Properties Limits Aerosol Forcing,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1922502117
Provided by the University of Leeds
Citations: Spacious environments offer a window into our cloudy past (2020, July 27) acquired on July 29, 2020 from https://phys.org/news/2020-07-pristine-environmentments-window-cloudy.html
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