Global Dimming

Okay. Let's see if I can explain this theory I saw on PBS the other night.

We have determined that global warming is taking place. The earth's temperature is going up. Over the eons there has been a relationship between rising carbon dioxide levels and global warming. I guess things are going off the charts lately. BUT --

Did you know that global dimming is also going on? Despite the increasing temperature, there is actually less sunlight reaching us. The sun isn't flaming out by the way.

However, there is as much as thirty per cent less sunlight reaching the earth in parts of Siberia, a trend that has taken place over the last fifty years. The amount if reduction is sixteen per cent in the U.S.

You would think those two things -- less sun, more heat -- would be mutually exclusive. Hang on. There is more.

The pan evaporation rate has been reduced by 100 ml in some places during recent years. This refers to the amount of evaporation of water from a container [a pan, who knew?] measured daily. For a hundred years there have been people around the world who go out back every day and check how much water is gone from the tank. Then they fill the pan back up.

Apparently there is a direct correlation between the amount of water evaporation in a given area and the amount of sunlight reduction. 

Here again you would expect more water to evaporate when the temperature goes up.

AHA!  Apparently evaporation isn't affected as much by temperature. Instead it is affected by photons from the sun that interact with the water molecules, causing the water to become vapor. More sunlight, more photons, more evaporation. And vice versa. Wind and humidity are two other factors. Temperature isn't.

How did we discover there was less sunlight hitting the earth? Some guy got curious. The reduction of sunlight from jet trails alone was discovered following 911, when all the planes in the US were grounded for weeks and the sky cleared.

Air pollution has also made a huge contribution to the reduction in sunlight and evaporation. Also global warming. The particulates in the pollutiion reflect the sunlight back to the earth and may be the greatest contributor to global warming.

We have more air pollution from many sources. Therefore there are more particles in the air that act like mirrors to reflect heat from the sun back to earth, increasing the temperature.

The air pollution that causes more heat simultaneously blocks the sun's photons from reaching the earth. The warm air melts the glaciers and ice packs, which is bad news for polar bears. The lack of evaporation means Venice will soon be under water.

So fix the air pollution and the earth cools off. The oceans evaporate more, the polar bears don't become extinct, and you can take that gondola ride on your honeymoon.

I wonder what kind of time we have on this one.