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Monday, April 18, 2011

James Hansen et al.: Earth's energy imbalance and implications

Earth's Energy Imbalance and Implications

James Hansen, Makiko Sato, Pushker Kharecha (NASA Goddard Institute for Space Studies, New York, NY 10025, and Columbia University Earth Institute, New York, NY 10027, U.S.A.) and Karina von Schuckmann (Centre National de la Recherche Scientifique, Laboratoire de Physique des Oceans, IFREMER, Brest, France)


Improving observations of ocean temperature confirm that Earth is absorbing more energy from the sun than it is radiating to space as heat, even during the recent solar minimum. This energy imbalance provides fundamental verification of the dominant role of the human-made greenhouse effect in driving global climate change. Observed surface temperature change and ocean heat gain constrain the net climate forcing and ocean mixing rates. We conclude that most climate models mix heat too efficiently into the deep ocean and as a result underestimate the negative forcing by human-made aerosols. Aerosol climate forcing today is inferred to be ‒1.6 ± 0.3 W/m² implying substantial aerosol indirect climate forcing via cloud changes. Continued failure to quantify the specific origins of this large forcing is untenable, as knowledge of changing aerosol effects is needed to understand future climate change. A recent decrease in ocean heat uptake was caused by a delayed rebound effect from Mount Pinatubo aerosols and a deep prolonged solar minimum. Observed sea level rise during the Argo float era can readily be accounted for by thermal expansion of the ocean and ice melt, but the ascendency of ice melt leads us to anticipate a near-term acceleration in the rate of sea level rise.

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