The ancient atmosphere provides a window to our cloudy past


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A new study uses satellite data over the Southern Hemisphere to understand global cloud composition during the Industrial Revolution. This research is one of the biggest uncertainties in today’s climate models – the long-term effect of small atmospheric particles on climate change.


Climate models currently include the global warming effects of greenhouse gases as well as the cooling effects of atmospheric aerosols. The small particles that make up these aerosols are produced by man-made sources such as emissions from cars and industry, as well as natural sources such as phytoplankton and sea spray.

They can directly affect the flow of sunlight and heat within the Earth’s atmosphere as well as interact with clouds. One way they do this is by increasing the ability of the clouds to reflect sunlight back into their small concentration. This in turn cools the planet. Sunlight reflected in space is referred to as the albedo of the Earth.

However, there is a very limited understanding of how aerosol concentration has changed between early industrial times and current times. This lack of information restricts the ability of climate models to accurately estimate the long-term effects of aerosols on global temperatures — and how much they may have in the future.

Now, an international study led by the universities of Leeds and Washington has assumed that remote, ancient parts of the Southern Hemisphere provide a window into which the early industrial environment resembled.

The team used satellite measurements of cloud droplet density in the Northern Hemisphere’s atmosphere — much more polluted with today’s industrial aerosols and from the relatively ancient Southern Ocean.

He used these measurements to determine potential changes due to industrial aerosols in the albedo of the Earth since 1850.

The result, published today in the magazine PNAS, Suggests that early-industrial aerosol concentrations and cloud droplets numbers were currently much higher than many global climate models. This may mean that man-made atmospheric aerosols are not giving strong cooling effects as some climate models estimate. The study suggests that the effect is likely to be more moderate.

Co-lead author, research fellow at the School of Earth and Environment in Leeds, Daniel McCoy said: “The limitations in our ability to measure aerosols in early industrial environments make it difficult to reduce uncertainties about how much warming there will be in the 21st. In the century.

“Ice cores provide carbon dioxide concentrations for millennia in the past, but aerosols do not rotate in the same way. One way we can try to look back in time is that we have not polluted a part of the atmosphere. Check. So far.

“These remote areas allow us to have a glimpse into our past and this helps us understand the climate record and improve predictions of what will happen in the future.”

Isabel McCoy, co-lead author of the Department of Atmospheric Sciences in Washington, said: “The biggest surprise for us was how high the concentration of cloud droplets was in the clouds of the Southern Ocean. The way the concentration of cloud droplets increased in summer Tells us that ocean biology is playing an important role in establishing cloud brightness in unpublished oceans now and in the past.

“We observe high cloud droplets concentrations in satellite and aircraft observations, but not in climate models. This suggests that there are gaps in the model representation of aerosol – cloud interactions and aerosol production mechanisms in ancient environments.

“As we continue to observe ancient environments via satellite, aircraft, and ground platforms, we can improve the representation of complex mechanisms governing cloud brightness in climate models and increase the accuracy of our climate estimates Huh.”

Co-author Layton Regere, a research fellow at the School of Earth and Environment in Leeds, said: “The science that supports our climate model is improving all the time. These models are dealing with the most pressing and complex environmental questions. The modern era and climate scientists have always been upfront about the fact that uncertainties exist.

“We’re only going to reach the answers we need to deal with global warming by regularly questioning science. Our team used millions of variants of a model to explore all possible uncertainties, including It is equivalent to having a clinical trial with millions of participants.

“We hope that our findings have inspired our work as well as studies on the detailed process of aerosol production and aerosol – cloud interactions in ancient environments, which will help in the development of next-generation climate models.”

The paper is published in “Hemispheric Contrast in Cloud Microphysical Properties Constrains Aerosol Forcing” PNAS, 27 July 2020.


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more information:
Isabel L. McCoy al al., “Hemispheric Contrast Aerosol Forcing in Cloud Microphysical Properties,”. PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1922502117

Provided by University of Leeds

Quotes: Pristine environments provide a window to our cloud past (2020, 27 July) from 28 July 2020 to https://phys.org/news/2020-07-pristine-en enhancement- window-cloudy.html.

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