Greenhouse gas effect consistent over 420 million years

Mar 28, 2007

New calculations show that sensitivity of Earth's climate to changes in the greenhouse gas carbon dioxide (CO2) has been consistent for the last 420 million years, according to an article in Nature by geologists at Yale and Wesleyan Universities.

A popular predictor of future climate sensitivity is the change in global temperature produced by each doubling of CO2 in the atmosphere. This study confirms that in the Earth's past 420 million years, each doubling of atmospheric CO2 translates to an average global temperature increase of about 3° Celsius, or 5° Fahrenheit.

According to the authors, since there has continuously been life on the planet over this time span, there must be an ongoing balance between CO2 entering and leaving the atmosphere from the rocks and waters at Earth's surface. Their simulations examined a wide span of possible relationships between atmospheric CO2 and temperature and the likelihood they could have occurred based on proxy data from geological samples.

Most estimates of climate sensitivity have been based on computer simulations of climate or records of climate change over the past few decades to thousands of years, when carbon dioxide concentrations and global temperatures were similar to or lower than today. Such estimates could underestimate the magnitude of large climate-change events.

To keep Earth's carbon cycle in balance, atmospheric CO2 has varied over geologic time. Carbon-cycle models balance chemical reactions that involve carbon, such as photosynthesis and the formation of limestone, on a global scale. To better predict future trends in global warming, these researchers compared estimates from long-term modeling of Earth's carbon cycle with the recent proxy measurements of CO2.

This study used 500 data points in the geological records as "proxy data" and evaluated them in the context of the CO2 cycling models of co-author Robert Berner, professor emeritus of geology and geophysics at Yale who pioneered models of the balance of CO2 in the Earth and Earth's atmosphere.

"Proxy data are indirect measurements of CO2 — they are a measure of the effects of CO2," explained co-author Jeffrey Park, professor of geology and geophysics at Yale who created the computer simulations for the project. "While we cannot actually measure the CO2 that was in the atmosphere millions of years ago, we can measure the geologic record of its presence. For example, measurement of carbon isotopes in ancient ocean-plankton material reflects atmospheric CO2 concentrations."

Led by Dana L. Royer, assistant professor of Earth and Environmental Sciences at Wesleyan University, who did his graduate work in geology at Yale, the collaboration simulated 10,000 variations in the carbon-cycle processes such as the sensitivity of plant growth to extra CO2 in the atmosphere. They evaluated these variations for a range of atmospheric warming conditions, using the agreement with the geologic data to determine the most likely warming scenarios. The model-estimated atmospheric CO2 variations were tested against data from ancient rocks.

Other proxy measurements of soil, rock and fossils provided estimates of CO2 over the past 420 million years. Calculation of the climate sensitivity in this way did not require independent estimates of temperature. It incorporated information from times when the Earth was substantially warmer and colder than today, and reflects the sensitivity of the carbon-cycle balance over millions of years.

"Our results are consistent with estimates from shorter-term records, and indicate that climate sensitivity was almost certainly greater than 1.5, but less than 5.5 degrees Celsius over this period," said Park. "At those extremes of CO2 sensitivity, [1.5°C or 5.5°C] the carbon-cycle would have been in a 'perfect storm' condition."

Source: Yale University

Explore further: Radioisotope studies show the continental crust formed 3 billion years ago

Related Stories

New calculations to improve CO2 monitoring from space

Jun 15, 2015

How light of different colours is absorbed by carbon dioxide (CO2) can now be accurately predicted using new calculations developed by a UCL-led team of scientists. This will help climate scientists studying ...

Boreal peatlands not a global warming time bomb

Jun 10, 2015

To some scientists studying climate change, boreal peatlands are considered a potential ticking time bomb. With huge stores of carbon in peat, the fear is that rising global temperatures could cause the release of massive ...

Study reveals how rivers regulate global carbon cycle

May 13, 2015

Humans concerned about climate change are working to find ways of capturing excess carbon dioxide (CO2) from the atmosphere and sequestering it in the Earth. But Nature has its own methods for the remova ...

Recommended for you

ESA image: Northwest Sardinia

Jul 03, 2015

This image over part of the Italian island of Sardinia comes from the very first acquisition by the Sentinel-2A satellite.

Experiments open window on landscape formation

Jul 02, 2015

University of Oregon geologists have seen ridges and valleys form in real time and—even though the work was a fast-forwarded operation done in a laboratory setting—they now have an idea of how climate ...

NASA image: Canadian wildfires continue

Jul 02, 2015

Canada is reeling from an early fire season this year as dozens of fires ravage at least three provinces of the country. All of the following reports are as of July 2, 2015.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.