Two new research studies quantify greenhouse gas contribution and amplifying effect of CO2
It has long been understood that the natural greenhouse effect, the blanket of heat-trapping “greenhouse” gases, clouds, and water vapor keep Earth from being a frozen, ice-covered ball.
One principal skeptic argument regarding the role CO2 plays in global warming has been the vast preponderance of water vapor in the atmosphere as compared to carbon dioxide. The logic being that water vapor would thus be the driving factor in any global warming, and therefore carbon emissions play little or no role. But this line of thinking is fundamentally mistaken, ignoring the role CO2 plays on the amount of water vapor in the atmosphere.
Many studies have confirmed the role of CO2 and other greenhouse gases, but a recent study by Andrew Lacis at the NASA Goddard Institute for Space Studies (GISS), published earlier this month in the journal Science, further demonstrates that increasing concentration of carbon dioxide in particular leads to more greenhouse warming than from just the heat absorbed in the gas itself.
Gavin Schmidt, a climate scientist at GISS and lead author of a companion study published in the Journal of the Geophysical Research-Atmospheres, says that of all the previous research done on the interplay of water vapor, CO2, and other greenhouse gases, none have systematically estimated the contribution of the “main players” to the greenhouse effect. Schmidt’s work set out to do just that – quantify the role of the various greenhouse gases to global warming.
The contribution of the constituent atmospheric greenhouse gases “are among the most misquoted statistics in public discussions of climate change,” writes Schmidt’s colleagues in the report.
“The existing literature is quite confused,” Schmidt says. “If you ask a lot of climate scientists, straight up, ‘how much of the current greenhouse effect is due to carbon dioxide?’, you get all sorts of numbers.”
Schmidt’s study found that water vapor is indeed the largest single contributor to natural global warming, responsible for about 50 percent of the greenhouse effect. Following water vapor are clouds, contributing about 25 percent, and next comes carbon dioxide with 20 percent. The final 5 percent of the greenhouse effect comes from trace gases and aerosols – including methane and nitrous oxide. In other words, condensing gases – water vapor and clouds – comprise 75 percent of the greenhouse effect, and a variety of non-condensing gases only one quarter.
Condensing gas vs. non-condensing gas
Lacis’ research further showed that without the “non-condensing” gases in play, clouds and water vapor – that quickly condense and precipitate from the atmosphere – are unable to provide “the feedback mechanisms that amplify the greenhouse effect.” The climate modeling showed that without the non-condensing gases, Earth’s greenhouse effect quickly collapses, plunging Earth into a frozen wasteland, clearly demonstrating that despite it’s larger contribution of the greenhouse effect, it cannot sustain that contribution without the support of the non-condensing gases, of which CO2 is the major player.
“Our climate modeling simulation should be viewed as an experiment in atmospheric physics,” Lacis said, “illustrating a cause and effect problem which allowed us to gain a better understanding of the working mechanics of Earth’s greenhouse effect, and enabled us to demonstrate the direct relationship that exists between rising atmospheric carbon dioxide and rising global temperature.”
Research from both studies showed that a doubling of CO2 in the atmosphere amplifies the greenhouse effect by a factor of five.
“When carbon dioxide increases, more water vapor returns to the atmosphere. This is what helped to melt the glaciers that once covered New York City,” said GISS researcher David Rind. “Today we are in uncharted territory as carbon dioxide approaches 390 parts per million in what has been referred to as the ‘superinterglacial.'”
“The bottom line is that atmospheric carbon dioxide acts as a thermostat in regulating the temperature of Earth,” Lacis said. “The Intergovernmental Panel on Climate Change has fully documented the fact that industrial activity is responsible for the rapidly increasing levels of atmospheric carbon dioxide and other greenhouse gases. It is not surprising then that global warming can be linked directly to the observed increase in atmospheric carbon dioxide and to human industrial activity in general.”
Image credit: NASA GISS/ Lilly Del Valle