Sunday, October 19, 2008

We all need the polar ice caps

I need to get one more thing off my chest before I can breathe deeply and go to sleep. This morning, I heard a woman on the radio talking to someone who referred to the "global warming hoax". She countered that the polar ice caps are melting. The man asked who cares?

She could only mumble something about how she supposes the polar bears care.

Big sigh. It is clear that scientists are not getting through to the media. Let me try to explain why we all need the polar ice cap if we plan on continuing to live on this planet.

This is the oft-distributed graphic showing the Earth's radiative budget (that is a fancy term for energy in--energy out) from the Intergovernmental Panel on Climate Change (IPCC) report.

The units are watts per square meter, Wm-2. Globally averaged, 342 Wm-2 of energy from the Sun hits the earth and clouds reflect 77 Wm-2. 30 Wm-2, almost 10%, are reflected from the surface. From the vantage point of the sun, the earth appears as a disk (area = πr2 ), with a reflective ice cap in the middle, instead of a sphere (area = 4πr2 ).

The earth's rotational axis is tilted so that the poles point toward the sun. The polar ice caps are responsible for much of the 30 Wm-2 that reflect back out into space. Now visit the Sea Ice in Retreat web widget and see how the polar ice cap has shrunk in the last 10 years. You might wonder, what is the big deal if the Boreal summer polar ice cap covers only one half to two thirds of the area it used to cover? Does it matter if they reflect only 7% of the Sun's incident radiation instead of 9%? 2% is small potatoes!

That 342 Wm-2 (with minor variations in solar sunspot activity) is an average over the entire Earth's surface, 4πr2 , on both the day and night sides. You can bet that the solar radiation density for the part of the earth pointed directly at the sun is quite a bit higher than 342 Wm-2.

For extra credit, calculate the surface area of the earth and figure out how many extra watts we will get without the ice caps. Use an average for the earth's radius, say 6378 km.

Simply put, without the polar ice caps, we are all gonna fry.


Off to bed.

1 comment:

  1. I was going to take on your homework assignment when I came across this article on Scientific American (through Slashdot):

    "As early as 1965, when Al Gore was a freshman in college, a panel of distinguished environmental scientists warned President Lyndon B. Johnson that CO2 emissions from fossil fuels might cause 'marked changes in climate' that 'could be deleterious.' Yet the scientists did not so much as mention the possibility of reducing emissions. Instead they considered one idea: 'spreading very small reflective particles' over about five million square miles of ocean, so as to bounce about 1 percent more sunlight back to space — 'a wacky geoengineering solution.' In the decades since, geoengineering ideas never died, but they did get pushed to the fringe — they were widely perceived by scientists and environmentalists alike as silly and even immoral attempts to avoid addressing the root of the problem of global warming. Three recent developments have brought them back into the mainstream."