From the “this is not the looney chemtrails idea” and the “how much of this can be attributed to climate jet-setter Bill McKibben?” department, comes this data.
Guest essay by Don Spencer
The recent “hiatus” in the global temperature record has thrown a dark cloud on carbon dioxide’s position in explaining climate change. Whereas the temperature record has been relatively constant for the last fifteen or so years the atmospheric carbon dioxide concentration has increased more-or-less unabated casting doubt over its influence. Climatologists have been scrambling to explain the temperature hiatus as just that, a hiatus or pause, where the greenhouse energy is temporarily stored away in the ocean to [wreak] its vengeance on us at a later time.
But maybe the simpler explanation is that we are backing the wrong gas and water vapor is the really important greenhouse gas, after all it currently accounts for more than 85% of the current greenhouse effect that supports life on this planet. Water vapor is a more effective greenhouse gas than carbon dioxide by virtue of its asymmetric molecular structure that allows more vibration modes hence more opportunities to capture and adsorb radiant energy.
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere
The trouble is that global water vapor concentration is difficult to measure and even harder to pin on humans. However since WWII humans have been conducting a great atmospheric seeding experiment. Thousands of large flying machines have been circling the earth day and night releasing millions of tons of water vapor into the upper atmosphere. The fuel used is typically kerosene (C12H26); when a molecule of kerosene burns in oxygen we ideally get twelve molecules of carbon dioxide and thirteen molecules of water vapor and a bunch of heat.
To estimate the amount of water vapor and carbon dioxide released we can look at the global aviation fuel usage from 1984-2010 which was obtained from
http://www.indexmundi.com/energy.aspx?product=jet-fuel. Note these statistics include both kerosene and naphtha aviation fuels.
We can see the consumption was less than two million barrels/day in 1984 and has risen to about five million barrels/day in 2010. The growth rate since about 2004 has been modest due to significant improvements in airliner efficiency. In the next figure the GISS global temperature has been plotted against the aviation fuel consumption. The correlation is quite good, better in fact than that for carbon dioxide. So if we all stop flying will we save the earth? Maybe, maybe not, as correlation alone does not necessarily imply causality but we do have a viable hypothesis, water vapor is a significant greenhouse gas and we are injecting vast quantities of it into the atmosphere via air travel. The temperature hiatus (if it is a hiatus) is explained by lower consumption and emissions due to more efficient jet engines. If this mechanism were correct and we did stop emitting water vapor then the atmospheric water vapor would soon reach a lower equilibrium and the temperature should fall back.
It is interesting to speculate what might happen if we do back the wrong gas. We shut down our fossil systems; coal-fired power stations, hydrocarbon based transportation and replace these with say renewable or nuclear energy and develop a “green” hydrogen economy producing nothing but “clean” water vapor. We would stop our CO2 emissions but vastly increase our water vapor output. This could actually make the earth warmer so we must make sure we get it right. The right answer is not known, more real science is needed with all hypotheses on the table.