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    Global climate change

    Shading the Planet could Reduce Global Rainfall

    11/01/2013, 10:29:35 AM

    One controversial approach to reducing future global warming is geoengineering.

    Geoengineering is the intentional, large-scale technological manipulation of the Earth’s systems.

    However, a new international study has found that geoengineering could cause the average global precipitation to decrease by 4.5 percent and reduce critical monsoonal rainfall in North America, East Asia and other regions by 5-7 percent compared to pre-industrial conditions.

    This new study from the National Center for Atmospheric Research (NCAR) focused on efforts to shade the planet.


    The research team turned to 12 of the world’s leading climate models to simulate global precipitation patterns if the atmospheric level of carbon dioxide, a leading greenhouse gas, reached four times the level of the preindustrial era. They then simulated the effect of reduced incoming solar radiation on the global precipitation patterns, according to the NCAR/UCAR Atmospheric News.

    The team found that precipitation amounts and frequency, especially for heavy rain events, would decrease significantly. The effects were greater over land than over the ocean, and particularly pronounced during months of heavy, monsoonal rains. Monsoonal rains in the model simulations dropped by an average of 7 percent in North America, 6 percent in East Asia and South America, and 5 percent in South Africa. In India, however, the decrease was just 2 percent. Heavy precipitation further dropped in Western Europe and North America in summer. (via NCAR/UCAR)

    The two main reasons for this decrease in precipitation were the following.....

    1. As Earth is shaded and less solar heat reaches the surface, less water vapor is pumped into the atmosphere through evaporation.

    2. With more carbon dioxide in the atmosphere, plants partially close their stomata, the openings that allow them to take in carbon dioxide while releasing oxygen and water into the atmosphere. Partially shut stomata release less water, so the cooled atmosphere would also become even drier over land.

    “Geoengineering the planet doesn’t cure the problem,” says NCAR scientist Simone Tilmes, lead author of the new study. “Even if one of these techniques could keep global temperatures approximately balanced, precipitation would not return to preindustrial conditions.” (via NCAR/UCAR)

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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    Global climate change