Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Climate sensitivity to CO2 more limited than extreme projections

25.11.2011
A new study suggests that the rate of global warming from doubling of atmospheric carbon dioxide may be less than the most dire estimates of some previous studies – and, in fact, may be less severe than projected by the Intergovernmental Panel on Climate Change report in 2007.

Authors of the study, which was funded by the National Science Foundation and published online this week in the journal Science, say that global warming is real and that increases in atmospheric CO2 will have multiple serious impacts.

However, the most Draconian projections of temperature increases from the doubling of CO2 are unlikely.

"Many previous climate sensitivity studies have looked at the past only from 1850 through today, and not fully integrated paleoclimate date, especially on a global scale," said Andreas Schmittner, an Oregon State University researcher and lead author on the Science article. "When you reconstruct sea and land surface temperatures from the peak of the last Ice Age 21,000 years ago – which is referred to as the Last Glacial Maximum – and compare it with climate model simulations of that period, you get a much different picture.

"If these paleoclimatic constraints apply to the future, as predicted by our model, the results imply less probability of extreme climatic change than previously thought," Schmittner added.

Scientists have struggled for years trying to quantify "climate sensitivity" – which is how the Earth will respond to projected increases of atmospheric carbon dioxide. The 2007 IPCC report estimated that the air near the surface of the Earth would warm on average by 2 to 4.5 degrees (Celsius) with a doubling of atmospheric CO2 from pre-industrial standards. The mean, or "expected value" increase in the IPCC estimates was 3.0 degrees; most climate model studies use the doubling of CO2 as a basic index.

Some previous studies have claimed the impacts could be much more severe – as much as 10 degrees or higher with a doubling of CO2 – although these projections come with an acknowledged low probability. Studies based on data going back only to 1850 are affected by large uncertainties in the effects of dust and other small particles in the air that reflect sunlight and can influence clouds, known as "aerosol forcing," or by the absorption of heat by the oceans, the researchers say.

To lower the degree of uncertainty, Schmittner and his colleagues used a climate model with more data and found that there are constraints that preclude very high levels of climate sensitivity.

The researchers compiled land and ocean surface temperature reconstructions from the Last Glacial Maximum and created a global map of those temperatures. During this time, atmospheric CO2 was about a third less than before the Industrial Revolution, and levels of methane and nitrous oxide were much lower. Because much of the northern latitudes were covered in ice and snow, sea levels were lower, the climate was drier (less precipitation), and there was more dust in the air.

All these factor, which contributed to cooling the Earth's surface, were included in their climate model simulations.

The new data changed the assessment of climate models in many ways, said Schmittner, an associate professor in OSU's College of Earth, Ocean, and Atmospheric Sciences. The researchers' reconstruction of temperatures has greater spatial coverage and showed less cooling during the Ice Age than most previous studies.

High sensitivity climate models – more than 6 degrees – suggest that the low levels of atmospheric CO2 during the Last Glacial Maximum would result in a "runaway effect" that would have left the Earth completely ice-covered.

"Clearly, that didn't happen," Schmittner said. "Though the Earth then was covered by much more ice and snow than it is today, the ice sheets didn't extend beyond latitudes of about 40 degrees, and the tropics and subtropics were largely ice-free – except at high altitudes. These high-sensitivity models overestimate cooling."

On the other hand, models with low climate sensitivity – less than 1.3 degrees – underestimate the cooling almost everywhere at the Last Glacial Maximum, the researchers say. The closest match, with a much lower degree of uncertainty than most other studies, suggests climate sensitivity is about 2.4 degrees.

However, uncertainty levels may be underestimated because the model simulations did not take into account uncertainties arising from how cloud changes reflect sunlight, Schmittner said.

Reconstructing sea and land surface temperatures from 21,000 years ago is a complex task involving the examination of ices cores, bore holes, fossils of marine and terrestrial organisms, seafloor sediments and other factors. Sediment cores, for example, contain different biological assemblages found in different temperature regimes and can be used to infer past temperatures based on analogs in modern ocean conditions.

"When we first looked at the paleoclimatic data, I was struck by the small cooling of the ocean," Schmittner said. "On average, the ocean was only about two degrees (Celsius) cooler than it is today, yet the planet was completely different – huge ice sheets over North America and northern Europe, more sea ice and snow, different vegetation, lower sea levels and more dust in the air.

"It shows that even very small changes in the ocean's surface temperature can have an enormous impact elsewhere, particularly over land areas at mid- to high-latitudes," he added.

Schmittner said continued unabated fossil fuel use could lead to similar warming of the sea surface as reconstruction shows happened between the Last Glacial Maximum and today.

"Hence, drastic changes over land can be expected," he said. "However, our study implies that we still have time to prevent that from happening, if we make a concerted effort to change course soon."

Other authors on the study include Peter Clark and Alan Mix of OSU; Nathan Urban, Princeton University; Jeremy Shakun, Harvard University; Natalie Mahowald, Cornell University; Patrick Bartlein, University of Oregon; and Antoni Rosell-Mele, University of Barcelona.

Andreas Schmittner | EurekAlert!
Further information:
http://www.oregonstate.edu

More articles from Earth Sciences:

nachricht NASA eyes Pineapple Express soaking California
24.02.2017 | NASA/Goddard Space Flight Center

nachricht 'Quartz' crystals at the Earth's core power its magnetic field
23.02.2017 | Tokyo Institute of Technology

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

NASA eyes Pineapple Express soaking California

24.02.2017 | Earth Sciences

New gene for atrazine resistance identified in waterhemp

24.02.2017 | Agricultural and Forestry Science

New Mechanisms of Gene Inactivation may prevent Aging and Cancer

24.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>