Cold Air Rises – a new study challenges climate model

A new study published by the University of California, Berkley; and funded by the David and Lucille Packard Foundation and the U.S. Department of Energy has identified an unexpected aspect of energy movement through the atmosphere. Conventional wisdom is that warm air will rise above cool air. This study has identified that the humidity of the air has a significant impact on the dynamics of atmospheric movement, and as a result, in the tropics, the lightness of water vapour results in cooler moist air rising, while warmer, drier air sinks.

The study found that the lightness of water vapor increases Earth’s thermal emission by about 1-3 watts per square meter over the tropics. That value compares with the amount of energy captured by doubling carbon dioxide in the atmosphere. The authors’ calculations further suggest that the radiative effects of vapor buoyancy increase exponentially with climate warming. The abstract states:

Moist air is lighter than dry air at the same temperature, pressure, and volume because the molecular weight of water is less than that of dry air. We call this the vapor buoyancy effect. Although this effect is well documented, its impact on Earth’s climate has been overlooked. Here, we show that the lightness of water vapor helps to stabilize tropical climate by increasing the outgoing longwave radiation (OLR). In the tropical atmosphere, buoyancy is horizontally uniform. Then, the vapor buoyancy in the moist regions must be balanced by warmer temperatures in the dry regions of the tropical atmosphere. These higher temperatures increase tropical OLR. This radiative effect increases with warming, leading to a negative climate feedback. At a near present-day surface temperature, vapor buoyancy is responsible for a radiative effect of 1 W/m2 and a negative climate feedback of about 0.15 W/m2 per kelvin.

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