Everyone talks about global warming, but it’s not easy to get one’s mind around just how much heat we’re talking about. Even more difficult is putting that heat energy in terms that the average layperson can grasp. Fortunately, some scientists are making an effort to do just that.
In a recent paper in Geophysical Research Letters, “Observed changes in surface atmospheric energy over land,” Thomas Peterson, of NOAA’s National Climatic Data Center in Asheville, NC, Katharine M. Willett of the Met Office Hadley Centre in Exeter, UK, and and Peter W. Thorne, who works alongside Peterson at the Cooperative Institute for Climate and Satellites, try to separate the various elements of all that energy being trapped by the greenhouse effect. There’s surface temperature, kinetic energy (wind) and latent heat (energy associated with water changes from one state to another, such as during evaporation).
All that is useful stuff from people who make their living studying climate. But what’s really interesting for our purposes is the team’s effort to express the energy being absorbed by the atmosphere. As part of the paper’s concluding section, they convert that energy into a gravitational equivalent: the energy required to lift an object:
The density of the atmosphere in lowâlying land areas is approximately 1.2 kg m [Committee on Extension to the Standard Atmosphere, 1976]. So a cylinder of air 100 meters in diameter and two-meter-high holds approximately 18,800 kg of air. Our analysis indicates that on average, this amount of air is gaining energy at a rate of 1.1 Ã 107 J decadeâ1. The Gravitational Potential Energy (in joules) of an object held above the earth equals the mass of the object, times gravity, times the distance it is above the earth. The heaviest car we own, Dr. Thorne’s SUV, weighs 1,535 kg and our lightest vehicle, Dr. Willett’s bicycle, weighs 9.5 kg. For these objects to gain the equivalent amount of gravitational potential energy as this two-m-tall by 100-m-diameter cylinder of air gained in heat content, the car would have to rise 700 meters decadeâ1 while after 10 years the bicycle would be just above the mesosphere at an elevation of 110 km.
Doing a little bit more math, and we can apply all that the planet as a whole:
… a two-meter-high layer of the atmosphere covering the global land surface would contain 3.37 Ã 1014 kg of air and be gaining heat content at a rate of 1.9 Ã 1017 J decadeâ1. This seems like a tremendous amount of energy and it is. Yet it is a drop in the bucket, three orders of magnitude less than the concurrent increase in heat content of the top two meters of the ocean and five orders of magnitude less than the concurrent increases in ocean heat content from 0 to 700 m depth.
That’s a lot of heavy lifting.
Peterson, T., Willett, K., & Thorne, P. (2011). Observed changes in surface atmospheric energy over land Geophysical Research Letters, 38 (16) DOI: 10.1029/2011GL048442