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Scientists studying the last major period of intense global warming have more bad news: The atmosphere, it seems, is even more sensitive of carbon emissions than previously thought.
According to geologists at Yale University, a relatively small increase in atmospheric carbon dioxide was responsible for a significant increase in temperature—as much as three or four degrees Celcius—during the Pliocene era three to 5 million years ago.
Using current models, scientists estimate the planet's climate sensitivity—the mean global temperature response to a doubling of carbon dioxide in the atmosphere—to be between 1.5 and 4.5 degrees Celsius. Mark Pagani, associate professor of geology and geophysics at Yale, explained:
These models take into account only relatively fast feedbacks, such as changes in atmospheric water vapor and the distribution of sea ice, clouds and aerosols...we wanted to look at Earth-system climate sensitivity, which includes the effects of long-term feedbacks such as change in continental ice-sheets, terrestrial ecosystems and greenhouse gases other than CO2.
The team's research showed that, over the past five million years, a small change in atmospheric carbon has been responsible for significant increased in temperature. Atmospheric carbon during the Pliocene reached a level between 365 and 415 parts per million, but was associated with an average global temperature two to three degrees higher than that of today.
Noting that the commonly accepted concentration of carbon in the atmosphere is 386 ppm, Pagani commented that "this work and other ancient climate reconstructions reveal that Earth's climate is more sensitive to atmospheric carbon dioxide than is discussed in policy circles."
There is no reason, Pagani explains, for us to assume today's earth will respond differently to changes in atmospheric carbon than the earth of five million years ago did. If this is the case, "we should expect a couple of degrees of continued warming even if we held CO2 concentrations at the current level."
Read more about climate modeling:
Earth's Temperature 30-50% More Sensitive to CO2 than Previously Thought
Animated Climate Model By Geophysical Fluid Dynamics Laboratory
Climate Versus Economy: Yale Model Allows You to Decide
A Breakthrough in Climate Modeling Shows Past Temperatures and Future Changes