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Energy and Atmospheric Carbon Dioxide

Paul Kando

Two studies at NASA’s Goddard Institute for Space Studies (GISS) examined the nature of Earth's greenhouse effect clarifying the role that greenhouse gases and clouds play in “trapping heat”, i.e. absorbing infrared radiation that would otherwise escape into space. The researchers found that non-condensing greenhouse gases -- carbon dioxide (CO2) methane, nitrous oxide, ozone, and chlorofluorocarbons – are at the core of Earth’s greenhouse effect.

CO2 levels over the last 10,000 years
photo credit: skeptical science

Various materials in the atmosphere contribute differently to the greenhouse effect. Some do it through “forcings” – directly driving or "forcing" the climate system to change. Others do it through feedbacks that amplify the impact of forcings. Water vapor and clouds, for instance, are major contributors to the greenhouse effect, but climate modeling studies show that without CO2 and other non-condensing greenhouse gases, water vapor and clouds would be unable to contribute to the warming effect. Therefore the planet's temperature ultimately depends on the atmospheric level of CO2.

In global climate modeling described in Science magazine scientists zeroed out all non-condensing greenhouse gases and aerosols. The model was then run forward in time to see what would happen to the greenhouse effect. The result: Without CO2 and the other non-condensing greenhouse gases Earth’s greenhouse effect would collapse. In the cool atmosphere water vapor would condense, plunging the Earth into an ice age. In short, while water vapor contributes 50% of the total greenhouse warming, it does so only through a feedback process, which cannot by itself sustain the greenhouse effect.

CO2 is responsible for 20% of the greenhouse effect, other non-condensing gases make up another 5% and water vapor and clouds together account for 75%. Still, it is the 25% non-condensing gas component, which includes CO2, that sustains the greenhouse effect. In effect, CO2 causes 80% of the radiative forcing.

Climate modeling provides researchers with a better understanding of the working mechanics of Earth’s greenhouse effect, enabling them to demonstrate the direct relationship between rising atmospheric CO2 and rising global temperature.

The geologic record shows that the atmospheric CO2level has fluctuated between about 180 parts per million (ppm) during ice ages, and about 280 ppm during warmer interglacial periods. Over the past century, the global mean temperature has increased by nearly 1ºC (1.8ºF), and the global mean temperature difference between ice ages and interglacial periods is estimated to be only about 5ºC (9ºF).

When atmospheric CO2 increases, warming occurs. More water evaporates and more vapor accumulates in the atmosphere, warming it further. This is what helped melt the glaciers that once covered much of the US East Coast. But today's above 400 ppm atmospheric CO2 level puts us into uncharted territory.

To sum up, atmospheric CO2 acts like a thermostat that regulates the temperature of our planet. As the Intergovernmental Panel on Climate Change (IPCC) has documented, human activity is responsible for the rapidly increasing levels of atmospheric CO2 and other greenhouse gases. Global warming is directly linked to the observed increase of atmospheric CO2, and thus to humans burning carbon-based fuels.

Some still fool themselves by denying this, even though there is conclusive proof. That’s what we will explore next week.