Carbon Dioxide Keeps Warming the Climate

The Earth's greenhouse effect is mainly caused by water vapors and clouds, but a new atmosphere-ocean climate modeling research shows that it is ultimately the carbon dioxide who is in control of the planet's temperature.

A study led by Goddard Institute for Space Studies (GISS) co-author Gavin Schmidt, accepted for publication in the Journal of Geophysical Research, says that CO2 triggers 20% of the greenhouse effect whereas water vapors and clouds have 75% of the responsibility, with other minor gases and aerosols accounting for the remaining 5%.

This study, as well as the one carried out by Andrew Lacis and colleagues at NASA's GISS in New York, says that it's actually the 25 percent of non-condensing gas components, CO2 included, that maintain the greenhouse effect.

This means that carbon dioxide is responsible for 80% of the radiative forcing that sustains global warming.

Lacis' study looked at the nature of the greenhouse effect and experimented to see the exact role played by CO2 and clouds in absorbing infrared radiation.

The team built a global climate model without the non-condensing greenhouse gases and ran it forward in time to see what happens.

In time, the Earth's greenhouse effect collapsed as it no longer had the support of the non-condensing gases (carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons).

The water vapor precipitated from the atmosphere, and the planet was plunged into an icebound state.

“Our climate modeling simulation should be viewed as an experiment in atmospheric physics, 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,” said Lacis.

The link between the planet's temperature and carbon dioxide has also been proved by geologic records of CO2 levels during ice ages – nearly180 parts per million, and interglacial periods – almost 280 parts per million.

The interesting thing is that the difference of the global temperature between an ice age period and an interglacial period is of only 5°C/9°F.

Co-author David Rind, of NASA's Goddard Institute for Space Studies explained that “when carbon dioxide increases, more water vapor returns to the atmosphere, [and] this is what helped to melt the glaciers that once covered New York City.

“Today we are in uncharted territory as carbon dioxide approaches 390 parts per million in what has been referred to as the 'superinterglacial.'”

And as Lacis said, “the bottom line is that atmospheric carbon dioxide acts as a thermostat in regulating the temperature of Earth.”

The study's results will be published today, October 15 in Science.