The new study uses satellite data from the southern hemisphere to understand the global composition of clouds during the Industrial Revolution. This study removes one of the biggest uncertainties in today̵7;s climate models – the long-term effects of small atmospheric particles on climate change.
Climate models currently include the global impact 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 automotive and industrial emissions, as well as natural sources such as phytoplankton and marine splashes.
They can directly affect the flow of sunlight and heat in the Earth’s atmosphere, as well as interact with clouds. One way to do this is to enhance the ability of clouds to reflect sunlight into space by increasing the concentration of their droplets. This in turn cools the planet. The amount of sunlight reflected in space is indicated by the Earth’s albedo.
However, there has been very limited understanding of how aerosol concentrations have changed from the early industrial period to the present day. This lack of information limits the ability of climate models to accurately estimate the long-term effects of aerosols on global temperatures and what effects they may have in the future.
An international study now led by the Universities of Leeds and Washington has found that remote, unspoiled parts of the Southern Hemisphere provide a window into what the early industrial atmosphere looked like.
The team used satellite measurements of cloud droplet concentrations in the atmosphere in the northern hemisphere – heavily polluted by today’s industrial aerosols – and above the relatively unspoiled Southern Ocean.
They used these measurements to estimate possible changes due to industrial aerosols in Earth albedo since the 1850s.
The results, published today in the journal PNAS, show that the concentration of early industrial aerosols and the number of cloud droplets were much higher than currently calculated for many global climate models. This may mean that man-made atmospheric aerosols do not have as strong a cooling effect as some climate models estimate. The study suggests that the impact is likely to be weaker.
The co-author, Daniel McCoy, a research fellow at Leeds School of Earth and the Environment, said: “Our ability to measure aerosols in an early industrial atmosphere makes it difficult to reduce uncertainty about what the heat will be. In the 21st century.
“Ice cores provide concentrations of carbon dioxide in the past millennia, but aerosols don’t accumulate as well. One way we can try to look back is to explore that part of the atmosphere that we haven’t polluted yet.
“These remote areas allow us to look at our past and it helps us understand climate change and improve our predictions of what will happen in the future.”
The 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 droplets is in the southern ocean cloud. The way the concentration of cloud droplets increases in the summer tells us that ocean biology plays an important role in determining the brightness of clouds in uncontaminated oceans now and in the past.
“We see high concentrations of cloud droplets in satellite and aircraft observations, but not in climate models. This suggests that there are gaps in the representation of aerosol-cloud interactions and aerosol production mechanisms in an intact environment.
“By continuing to monitor the pristine environment through satellite, aircraft and ground platforms, we can improve the representation of complex cloud-brightness control mechanisms in climate models and increase the accuracy of our climate forecasts.”
Co-author Leighton Regayre, a researcher at Leeds School of Earth and the Environment, said: “The science that supports our climate models is constantly evolving. These models address some of the most pressing and complex environmental issues. the modern era and climate scientists have always been prejudiced by the existence of uncertainty.
“We will only achieve the answers we need to combat global warming by regularly interrogating science. Our team has used millions of model variants to investigate all possible uncertainties, which equates to a clinical trial involving millions of participants.
“We hope that our findings, together with comprehensive studies of the aerosol production process and aerosol-cloud interactions in an unfamiliar environment, motivated by our work, will help to develop a new generation of climate models.”
The article “Hemispheric contrast in the microphysical properties of clouds limits aerosol tightening” is published PNAS, 2020 July 27
Fire aerosols are changing the productivity of terrestrial ecosystems as the climate changes
Isabel L. McCoy el. Al., “Hemisphere contrast due to the microphysical properties of clouds restricts aerosol.” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1922502117
Presented at the University of Leeds
Citation: Undefeated environments offer a window into our murky past (2020, July 27), Received in 2020. July 29, From https://phys.org/news/2020-07-pristine-environments-w window-cloudy.html
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