Worldwide atmospheric greenhouse gas concentrations reached record highs in 2013, according to a report from the World Meteorological Organization. The resulting radiative forcing averaged 2.9 watts per square meter (see chart at right).
(Click on chart for larger view.)
Let me explain. The earth constantly receives energy from the sun, and radiates it back into space. Greenhouse gases trap some of the radiation, holding it in the earth’s atmosphere rather than letting it escape into space. If energy is being absorbed at the same rate, but the rate at which it is radiated back into space is reduced, then the earth will warm. This is the basic theory behind global warming and the concern with greenhouse gases.
The difference between the rate at which the earth radiates energy into space today vs. the rate during pre-industrial times (the year 1750) is called radiative forcing. It represents how much excess energy the earth is holding compared to 1750.
So how much energy is that? Well, the earth is a big place. It’s surface area is 510.2 trillion square meters. At 2.9 watts per square meter, the Earth is holding an excess of 1.48 quadrillion watts of heat (1,480,000,000,000,000).
That’s a big number, it boggles the mind. But what does it mean – how much energy is 1.48 quadrillion watts? We could compare it to train locomotives. The largest locomotives in the world have a power output of about 5,400 kilowatts. Global radiative forcing would be roughly equal to the output of 274 million of them. Even that is such a large number it is hard to imagine, however.
Let’s compare it to the output of nuclear generating stations. We only have one in Missouri, the Callaway Nuclear Generating Station, so let’s use it for our comparison. The output of the Callaway Plant is 1,279 megawatts, so the solar forcing affecting the earth would be roughly equal to 1.16 million Callaway Plants. Imagine covering the earth with 1.16 million nuclear generating stations. (As of May, 2014, there were only 435 nuclear reactors operating around the world.)
Now, let’s break it down a bit. How much of that excess heat should be attributed to the United States? How much to Missouri? The surface area of the USA is 9,857,306 square kilometers. At 2.9 watts per square meter, that yields a total solar forcing of 28.59 trillion watts, the equivalent of 5.9 million locomotives, or 22,353 Callaway Nuclear Generating Stations.
The surface area of Missouri is 180,533 square kilometers. At 2.9 watts per square meter, that represents 523.5 billion watts of solar forcing, the equivalent of 96,944 locomotives, or 409 Callaway Nuclear Generating Stations. The campus of the Callaway Nuclear Generating Station is irregular, but it is roughly 1 mile across north-to-south, half-a-mile across east-to-west. If you kept with those dimensions, and said that each generating station had to have its own campus that size, then they would require a rectangular footprint that stretched from the Missouri-Iowa border on the north to Little Rock on the south, and from Independence on the west to St. Charles on the east.
Some may argue that the radiative forcing is small compared to the total energy budget of the earth, and therefore trivial. I disagree. The fact that it is small compared to the earth’s total energy budget does not make it trivial. If you had a fever of 104°, it would be small compared to your overall energy budget – an increase in temperature of less than 1%. But that would not make it trivial. In fact, it would be life-threatening.
The amount of excess energy represented by radiative forcing is significant, and on a human scale, it is large.
In an upcoming post, I will go into the gases contributing to radiative forcing.
World Meteorological Organization Global Atmosphere Watch. 2014. WMO Greenhouse Gas Bulletin. Accessed 11/21/14 at http://www.wmo.int/pages/prog/arep/gaw/ghg/GHGbulletin.html.
“List of Largest Locomotives.” Wikipedia. Accessed 11/21/14 at http://en.wikipedia.org/wiki/List_of_largest_locomotives.
Nuclear Energy Institute. World Statistics. http://www.nei.org/Knowledge-Center/Nuclear-Statistics/World-Statistics.
“Earth.” Wikipedia. Accessed on 11/11/14 at http://en.wikipedia.org/wiki/Earth.
“United States.” Wikipedia. Accessed 11/12/14 at http://en.wikipedia.org/wiki/United_States.
“Missouri.” Wikipedia. Accessed 11/12/14 at http://en.wikipedia.org/wiki/Missouri.
Unit Juggler. Accessed 11/11/14 at http://www.unitjuggler.com.