Saturday, August 27, 2011

The FLOOD / DROUGHT Paradox?



I've been asked to explain the apparent paradox of the planet seemingly getting drier, but also wetter.

The fact of the matter is that it cannot be more natural.

First, consider the fact that warmer air can "hold" more moisture than cooler air before saturation, or reaching the Dew Point. For example, air at 20C can hold 300% more moisture than air at 0C.

As a result of a warmer atmosphere today than a few decades ago, there is indeed a 5% increase in the absolute amount of water in the atmosphere now than then.


However, if the warmer air can hold, say, 15% more moisture before saturation than before, then, even given the 5% absolute increase in the atmospheric water content, the Relative Humidity would have declined by about 10%. Note from the following graph that the blue line, representing the relative humidity at an altitude of 6 miles, shows a decline of over 20% from 1950-2007.


Therefore, in the tropics and lower temperates, precipitation will likewise decline, thus causing droughts in these regions.

On the other hand, in the northern latitudes, where the air is still relatively cool, a local cold spot or cold front, or in the case of a hurricane, will dump 5% more precipitation than before, due to the 5% absolute increase in the atmosphere water content, thus causing floods.


Anthony Marr, Founder and President
Heal Our Planet Earth (HOPE)
Global Anti-Hunting Coalition (GAHC) (AM's 3rd-book-in-the-making)

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