There is a note in the "Science in the News" e-mail newsletter from Sigma Xi today that January 2007 was the warmest January on record. The Sigma Xi newsletter quotes from The Seattle Times newspaper. World-wide, January was 1.53°F warmer than the average or one-quarter degree warmer than the previous record for January.
In spite of a colder than normal February, the world is warming steadily. It seems to bother some folks that a local area, like North America for instance, can be colder than usual while the planet is growing steadily warmer. Let's see if I can explain the apparent paradox in understandable terms.
First, the heat balance. The planet gets its heat mainly from the Sun. Some solar radiation comes in through the atmosphere and warms the surface of the Earth. The rest of it is reflected back out into space, lost to us forever. In an equation, Total Solar Radiation = Absorbed Heat + Reflected Radiation. Rearranged,
Absorbed Heat = Total Solar Radiation - Reflected Radiation
The amount reflected and lost is regulated by the atmosphere. Carbon dioxide (CO2) and methane (CH4) are called "greenhouse gases" because they absorb some of that radiation that would otherwise be lost back out into Space. That is why the earth is getting warmer -- we are producing lots of gases that trap heat from the Sun, heat that would otherwise be lost into outer Space.
So how can a hotter Earth produce a colder February?
The climate engine of the Earth -- the air and the water -- operate a little like a steam engine or a gasoline engine. The more energy (heat) you put into it, the harder it can work. It's that simple!
The extra heat we are trapping in Earth's atmosphere and oceans is forcing the Climate Engine to drive the weather to more extreme conditions. Global Warming is going to mean hotter weather, colder weather, wetter weather, and drier weather, all at the same time. A warmer January globally is followed by a colder February locally in eastern North America. It's all part of a hotter, more energetic Earth.