Saturday, February 13, 2010

Climate Change and Snowstorms - It's All About the Energy

Snow on rosemary, 2/13/2010, Cary, NC

The story of climate change is the story of energy, in particular, the Earth's balance between incoming and outgoing energy. Our planet's energy equation begins with sunlight. More and more sunlight energy arrives at Earth with each passing day. That sunlight energy warms the ground, bodies of water, plants and animals. Each of those objects in turn radiates its own energy according to its temperature. Since those objects are much cooler than the sun, they radiate energy of a different wavelength than the sun. The sun radiates in the visible wavelengths, but the Earth and everything on it radiates in the infrared wavelengths, which are invisible to our eyes.

Greenhouse gases such as carbon dioxide and methane in our atmosphere are transparent to sunlight just like the nitrogen and oxygen that make up most of our air. However, what makes CO2 and methane effective greenhouse gases is their ability to absorb infrared radiation, something nitrogen and oxygen cannot do. So the greenhouse gases let in sunlight, which warms the Earth, but they do not let infrared radiation escape. Instead, they absorb that infrared radiation and themselves get warmer. As CO2 and methane get warmer, they radiate more infrared radiation themselves, much of it heading back towards the Earth, adding to the warming effects of sunlight.

So the more greenhouse gases reach the atmosphere, the more infrared radiation is absorbed, and the warmer the entire planet becomes. But why would a warmer planet mean more snow or more severe storms?

It's all about the energy. More sunlight coming in and less infrared radiation going out means more energy here. And more energy means higher temperatures, on average. But how can higher temperatures mean more snow?

Because it takes energy to evaporate water. As temperatures rise everywhere, water evaporates faster and faster. More water evaporates from the oceans, from lakes and rivers, even from moist soil. More water even evaporates through the tiny pores covering the leaves of plants growing around the world.

More water evaporation means more total water vapor in the atmosphere, and that inevitably leads to more precipitation. With temperatures above freezing, that precipitation comes down as rain. Drop the temperature below 32°F, and the precipitation comes down as snow or sleet or freezing rain.

Ask a native of Buffalo, New York about the role that water evaporation plays in snowfall. "Lake effect" snow results when water evaporates from a nearby lake - in the case of Buffalo, Lake Erie to the west or Lake Ontario to the north. More water evaporating into the air means more precipitation, and in the winter, even with the greenhouse effect, temperatures can drop below freezing and that precipitation will be frozen. And remember that one inch of rainfall can, if frozen, produce somewhere between 6 and 10 inches of snow.

What is it about a warmer planet that can lead to more severe storms? Storms, with strong winds, heavy precipitation, perhaps even lightning, release a great deal of energy. Where does that energy come from?

Much of the energy in a storm comes from the water vapor in the air within the storm. Remember that it took energy to evaporate that water in the first place. Water vapor carries all the energy it took to evaporate it up into the atmosphere. And as that air rises it cools, and the water vapor cools with it. Eventually the cooling water vapor does not have enough energy to stay a gas, and condenses back into tiny droplets of liquid water, forming clouds. Condensation releases the energy it took to evaporate the water, and that released energy passes to the surrounding air, adding to the strength of the storm.

Global warming driven by a stronger greenhouse effect upsets the energy balance of the planet. More energy evaporates more water. More water vapor makes more precipitation and stronger storms. And in the winter, more precipitation and stronger storms can mean snow and blizzard conditions. Greg Craven, a high school physics teacher, suggested global "weirding" might be a better title than global warming. And that was before the 2010 snowpocalypse hit the mid-Atlantic states.


  1. Llewellyn Reese tried to post this comment to no avail, so I have posted it for him:

    Very good article, except that I hate hate hate the phrase "global weirding". Most of the implications - yes, including stronger snowstorms - are relatively straightforward, and not all that "weird" once one has a halfway decent science background. The fact that warmer air, and much more importantly, warmer water (all other things being equal) generally results in more snow and stronger snow storms, so long as it is still cold enough to snow, is talked about in a good many popular books on weather, including many that didn't mention global warming at all, going back as far as I can remember.

    It's better to teach people that global warming, like many other things in life, can have surprising implications. It's better to retain the phrase which indicates the direction of the change in global average temperature anomalies. I suspect "global weirding" encourages "Day After Tomorrow" style thinking, resulting in confusion.

  2. Thanks for the clear explanation - very helpful. I visited from Scientia Pro Publica, by the way. Cheers!