The warming effect of human-induced greenhouse gases is a given, but an international team of researchers is now seeking to predict the future influence. While science is making progress, the answers are still far from exact, say researchers from the Hebrew University of Jerusalem, the University of New South Wales, the University of Washington and the US National Oceanic and Atmospheric Administration.
The international study shows that there are still many unknowns about the main interaction between aerosols and clouds, which can counteract part of the effects of climate warming by increasing the amount of sunlight that is reflected back to space.
Further progress on the understanding of aerosol-cloud interactions and their effects on climate is being hampered by limited observational capabilities and coarse climate models, says Prof. Daniel Rosenfeld of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem. Rosenfeld wrote an article – recently published in Science – in cooperation with Dr. Steven Sherwood of the University of New South Wales, Sydney, Dr. Robert Wood of the University of Washington, Seattle, and Dr. Leo Donner of the US National Oceanic and Atmospheric Administration.
Their studies show a much more complicated picture of aerosol-cloud interactions than considered previously. Depending on the meteorological circumstances, aerosols can have dramatic effects of either increasing or decreasing the cloud sun-deflecting effect, the researchers say.
Explicit computer simulations of these processes even at the scale of a whole cloud or multi-cloud system, let alone that of the planet, require hundreds of hours on the most powerful computers available. Therefore, a sufficiently accurate simulation of these processes at a global scale is still impractical.
However, researchers have been able to create groundbreaking simulations in which models were formulated presenting simplified schemes of cloud-aerosol interactions. This approach offers the potential for model runs that resolve clouds on a global scale for time scales up to several years, but climate simulations on a scale of a century are still not feasible.
The scientists say achieving the required improvement in observations and simulations is within technological reach — provided that the financial resources are invested.
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