Sunday, March 1, 2009
Change in Heat Content
It is normal to think of Global Warming in terms of rising air temperatures. However, the earth is composed of many things that can absorb heat energy. Warming of the oceans and melting ice and permafrost are some other ways that the earth can warm. Interestingly, there is not as much coverage on all the other parts of the earth as they don’t have as much of an impact on our daily lives. The IPCC Technical Summary has some good technical information of where and how the globe is warming.
Figure TS.15 on page 47 list the changes of earths energy content (heating) in terms of 10^22 joules. By far the largest component of the earths energy system are the Oceans. Not just the surface of the oceans, but their entire depth. Ice (Glaciers, Greenland, Antarctica and Sea Ice), the Continents and the Atmosphere are the other main components. It is a simple matter to convert these values to percentages as shown the following:
Percent of Heating (1961-2003)
Notice that while the atmosphere has warmed, both the oceans and ice have absorbed more heat. To put this into perspective, the rest of the earth has absorbed 50 times as much heat as the atmosphere!
Some skeptics like to suggest that global warming is due to changes in the earth’s oceans, implying that the atmosphere has warmed because less heat is being absorbed by the oceans. However, as can be seen from above, just the opposite is true. That is every major component of the earth is warming with the oceans absorbing the bulk of it.
It’s also interesting to consider how the oceans warm. Warm water is less dense and tends to float on the surface, while the deepest water is the coldest. This make it difficult to transport heat energy into the depths of the oceans and theoretically it would be possible for a stagnant condition to occur. That is the surface waters could warm significantly without heating the depths. Normally heat is transported to the depths from mixing thru wind and wave action along with the meridional overturning circulation. However, long term records of the relative strengths of these processes are sparse and computer models are all over the place with predictions. Of course, the science will gradually advance to better understand the coming changes, but there could be some surprises along the way.