Know Your Numbers

Winter                                                            Seed Catalog Moon

I’ve finished the first two lessons and the first week of Climate Change in 4 Dimensions. There is so much here already.   First is how simple the proofs are for the reality of climate change.  And how they might be difficult to believe at first.

The concentration of carbon dioxide in the atmosphere is the best example.  It’s expressed in ppm’s or parts per million.  At its pre-industrial revolution norm it was around 280 ppm’s.  Now, if you check out the latest ppm data from Mauna Loa on CO2 Now, it was at 396.1 ppm.  That’s parts per million.  Here’s a graphic to make it harder to grasp CO2′s significance:

atmosphere composition


How, any sensible person might ask, can such a tiny, tiny portion of the atmosphere create problems?  Here’s the answer.  Nitrogen and oxygen, the major components of earth’s atmosphere are transparent to sunlight coming and going.  That is, they don’t impeded it in either direction.  CO2, methane, water vapor, and nitrous oxide, these last three in even smaller ppm’s than CO2, are transparent to sunlight coming into the atmosphere.  They let it get through.

They are not, however, transparent to infrared energy transmitted back out into space.  Their relatively homogenous presence over the whole globe, due to the mixing factor of the winds, means that their effect is felt worldwide.   Their amount of opaqueness is sufficient to force back to the lower atmosphere and surface of the earth infrared energy.  If you want a brief summary of these mechanism, go here.*



*Here’s what all scientists agreed they knew by 1988

To stay at a constant temperature, the Earth must radiate as much energy as it receives from the Sun. We receive this energy mostly as visible light which warms the surface. Being much cooler than the Sun, the Earth radiates most of its energy as infrared rays. A calculation using basic laws of physics shows that a planet at our distance from the Sun, emitting the same total amount of energy as it receives, will have a temperature well below freezing. Then why is the actual average surface temperature higher, about 14°C? Infrared radiation beaming up from the surface is intercepted by “greenhouse” gas molecules in the lower atmosphere, and that keeps the lower atmosphere and the surface warm. The radiation that finally escapes is mostly emitted from higher levels of the atmosphere, levels that are indeed well below freezing (-18°C, for details see the essay on simple models).

The nitrogen and oxygen gases that make up most of the atmosphere don’t intercept infrared radiation. The most important greenhouse gases are water vapor and carbon dioxide (CO2). The level of carbon dioxide in the atmosphere was observed to be rising rapidly, and the only reasonable explanation was that this was due to the enormous emissions from human activities.

A rather straightforward calculation showed that doubling the level of carbon dioxide in the atmosphere… which would arrive in the late 21st century if no steps were taken to curb emissions… should raise the temperature of the surface roughly one degree C. However, a warmer atmosphere would hold more water vapor, which ought to cause another degree or so of warming. Beyond that the calculations got problematic. Cloudiness was likely to change in ways that could either enhance or diminish the warming, and scientists did not understand the complex processes well. Moreover, humanity was emitting ever increasing amounts of smoke and other pollution; again scientists were not sure how this might affect climate. Only better observations and computer models could attempt to project the outcome.