Climate Wire: The underlying science behind climate models has greatly improved in the past couple of decades, partly due to a concerted research effort known as the Coupled Model Intercomparison Project. Through that work, scientists have improved the accuracy of climate models and their representation of Earth’s physical processes.
Another type of model used to project climate impacts, however, still has significant uncertainty, researchers say. These models, called impact models, take the climate model outputs that show changes in the atmosphere and ocean systems and translate them into effects on things like agriculture, flooding, drought and even human health.
Such results would be incredibly useful for planners and policymakers, but impact models are still in their early stages, with somewhat unreliable projections.
That’s a major reason why scientists engaged at the Potsdam Institute for Climate Impact Research in Germany have been working to improve them. That effort, known as the Inter-Sectoral Impact Model Intercomparison Project, or ISI-MIP, was launched in early 2012.
Earlier this week, a group of more than 30 research teams spanning 12 countries all involved in the ISI-MIP project published their first results in a special issue of the journal Proceedings of the National Academy of Sciences
Impact models are “the second step after the climate models, and it’s a relevant step for what climate change means for humans,” said Katja Frieler, a climate impacts researcher at the Potsdam Institute who is coordinating the project.
While the results from many of the model runs have considerable uncertainty, this first effort is part of a comparative, iterative process similar to the one that early climate models went through. Eventually, the effort will make impact models more robust, Frieler said.
“Even if there are differences between the models, it’s extremely helpful to analyze where they come from and where actually our uncertainties lie,” she said.
The papers from the project were also submitted to the Working Group 2 of the Intergovernmental Panel on Climate Change, which will be able to use their results in its assessment of the impacts of climate change.
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One of the project’s studies, for example, explored climate change’s impact on hydrological drought, which is a type of drought associated with decreased runoff, leading to water shortages in rivers, aquifers, reservoirs and other parts of a watershed.
Led by Christel Prudhomme, hydrologist with the Centre for Ecology & Hydrology in Wallingford, England, researchers concluded that under all but one of seven global impact models used in their study, drought is expected to increase in both global extent and frequency by the end of the century.
Although this study uses a different metric for drought (earlier work focused on soil moisture), this finding is not qualitatively different from the existing body of research on climate change and drought, said Martin Hoerling, a meteorologist with the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory.
But an inconsistent result in Prudhomme’s work raises questions about how a warming planet might interact with the biosphere, potentially altering future drought projections.
One impact model used in the study, which takes into account how plants might adjust to an increase in carbon dioxide, did not show a significant increase in drought. Called the JULES model, it assumes that plants will “breathe” less in a CO2-enriched atmosphere and therefore will not lose as much water in the process.
“If the plants don’t dry up the soil as much, then you have more water available for runoff,” Prudhomme said.
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