Fire Earth

Earth is fighting to stay alive. Mass dieoffs, triggered by anthropogenic assault and fallout of planetary defense systems offsetting the impact, could begin anytime!

Posts Tagged ‘aerosols’

CO2 Controls Earth’s Temperature

Posted by feww on October 15, 2010

Atmospheric CO2  acts as Earth’s thermostat: Study

A new modeling study shows that the planet’s temperature is controlled by the atmospheric CO2, NASA says.


Various atmospheric components differ in their contributions to the greenhouse effect, some through feedbacks and some through forcings. Without carbon dioxide and other non-condensing greenhouse gases, water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect. Source: NASA GISS

Water vapor and clouds are the major contributors to Earth’s greenhouse effect, but a new atmosphere-ocean climate modeling study shows that the planet’s temperature ultimately depends on the atmospheric level of carbon dioxide.

The study, conducted by Andrew Lacis and colleagues at NASA’s Goddard Institute for Space Studies (GISS) in New York, examined the nature of Earth’s greenhouse effect and clarified the role that greenhouse gases and clouds play in absorbing outgoing infrared radiation. Notably, the team identified non-condensing greenhouse gases — such as carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons — as providing the core support for the terrestrial greenhouse effect.

Without non-condensing greenhouse gases, water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect. The study’s results will be published Friday, Oct. 15 in Science.

A companion study led by GISS co-author Gavin Schmidt that has been accepted for publication in the Journal of Geophysical Research shows that carbon dioxide accounts for about 20 percent of the greenhouse effect, water vapor and clouds together account for 75 percent, and minor gases and aerosols make up the remaining five percent. However, it is the 25 percent non-condensing greenhouse gas component, which includes carbon dioxide, that is the key factor in sustaining Earth’s greenhouse effect. By this accounting, carbon dioxide is responsible for 80 percent of the radiative forcing that sustains the Earth’s greenhouse effect.

The climate forcing experiment described in Science was simple in design and concept — all of the non-condensing greenhouse gases and aerosols were zeroed out, and the global climate model was run forward in time to see what would happen to the greenhouse effect. Without the sustaining support by the non-condensing greenhouse gases, Earth’s greenhouse effect collapsed as water vapor quickly precipitated from the atmosphere, plunging the model Earth into an icebound state — a clear demonstration that water vapor, although contributing 50 percent of the total greenhouse warming, acts as a feedback process, and as such, cannot by itself uphold the Earth’s greenhouse effect.

“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,” Lacis said.

The study ties in to the geologic record in which carbon dioxide levels have oscillated between approximately 180 parts per million during ice ages, and about 280 parts per million during warmer interglacial periods. To provide perspective to the nearly 1 C (1.8 F) increase in global temperature over the past century, it is estimated that the global mean temperature difference between the extremes of the ice age and interglacial periods is only about 5 C (9 F).

“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 co-author David Rind, of NASA’s Goddard Institute for Space Studies. “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.”

More Reading

by Kathryn Hansen, NASA’s Earth Science News

Related Links:

Posted in anthropogenic CO2, feedbacks, forcings, Global Warming, greenhouse effect, superinterglacial | Tagged: , , , | Leave a Comment »

Global temps could rise higher than expected

Posted by feww on December 21, 2009

Global temperatures could rise more than expected, new study shows

The kinds of increases in atmospheric carbon dioxide taking place today could have a significantly larger effect on global temperatures than previously thought, according to a new study led by Yale University geologists. Their findings appear December 20 in the advanced online edition of Nature Geoscience.

The team demonstrated that only a relatively small rise in atmospheric carbon dioxide (CO2) was associated with a period of substantial warming in the mid- and early-Pliocene era, between three to five million years ago, when temperatures were approximately 3 to 4 degrees Celsius warmer than they are today.

Climate sensitivity—the mean global temperature response to a doubling of the concentration of atmospheric CO2—is estimated to be 1.5 to 4.5 degrees Celsius, using current models.

“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,” said Mark Pagani, associate professor of geology and geophysics at Yale and lead author of the paper. “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.”

To do this, the team focused on the most recent episode of sustained global warmth with geography similar to today’s. Their reconstructed CO2 concentrations for the past five million years was used to estimate Earth-system climate sensitivity for a fully equilibrated state of the planet, and found that a relatively small rise in CO2 levels was associated with substantial global warming 4.5 million years ago. They also found that the global temperature was 2 to 3 degrees Celsius higher than today while CO2 levels were only between about 365 and 415 parts per million (ppm)—similar to today’s concentration of about 386 ppm.

“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,” Pagani said. “Since there is no indication that the future will behave differently than the past, we should expect a couple of degrees of continued warming even if we held CO2 concentrations at the current level.”

0O0

Other authors of the paper include Zhonghui Liu (Yale University and The University of Hong Kong), and Jonathan LaRiviere and Ana Christina Ravelo (University of California, Santa Cruz).

This study used samples provided by the Integrated Ocean Drilling Program and was funded by the National Science Foundation and the Yale Climate and Energy Institute.

Contact: Suzanne Taylor Muzzin
suzanne.taylormuzzin@yale.edu
Yale University

0O0

Global warming likely to be amplified by slow changes to Earth systems

Researchers studying a period of high carbon dioxide levels and warm climate several million years ago have concluded that slow changes such as melting ice sheets amplified the initial warming caused by greenhouse gases.

The study, published in the journal Nature Geoscience, found that a relatively small rise in atmospheric carbon dioxide levels was associated with substantial global warming about 4.5 million years ago during the early Pliocene.

Coauthor Christina Ravelo, professor of ocean sciences at the University of California, Santa Cruz, said the study indicates that the sensitivity of Earth’s temperature to increases in carbon dioxide in the atmosphere is greater than has been expected on the basis of climate models that only include rapid responses.

Carbon dioxide and other greenhouse gases trap heat in the atmosphere, leading to increased atmospheric and sea-surface temperatures. Relatively rapid feedbacks include changes in atmospheric water vapor, clouds, and sea ice. These short-term changes probably set in motion long-term changes in other factors–such as the extent of continental ice sheets, vegetation cover on land, and deep ocean circulation–that lead to additional global warming, Ravelo said.

“The implication is that these slow components of the Earth system, once they have time to change and equilibrate, may amplify the effects of small changes in the greenhouse gas composition of the atmosphere,” she said.

The researchers used sediment cores drilled from the seafloor at six different locations around the world to reconstruct carbon dioxide levels over the past five million years. They found that during the early and middle Pliocene (3 to 5 million years ago), when average global temperatures were at least 2 to 3 degrees Celsius warmer than today, the concentration of carbon dioxide in the atmosphere was similar to today’s levels, about 30 percent higher than preindustrial levels.

“Since there is no indication that the future will behave differently than the past, we should expect a couple of degrees of continued warming even if we held carbon dioxide concentrations at the current level,” said lead author Mark Pagani, an associate professor of geology and geophysics at Yale University.

0O0

Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California – Santa Cruz

0O0

Related Links:

Posted in Climate Change, CO2, Geophysics, greenhouse gasses, Warming | Tagged: , , , , , | 2 Comments »