Study warns climate change is "irreversible"

Many effects of global warming are irreversible and global temperatures could remain high for 1,000 years even if carbon emissions could be halted, warn scientists.

This content was published on January 27, 2009 - 18:01

The study by a team of United States-Swiss-French researchers comes as President Barack Obama announces a review of vehicle emission standards and promises global leadership on climate change as part of his new green agenda.

"People think that if we start doing something about carbon emissions the problem will just go away... this is not the case," climate researcher Gian-Kaspar Plattner, of the Swiss Federal Institute of Technology in Zurich, told swissinfo.

Kasper and his Swiss colleague, Reto Knutti, were co-authors of the scientific paper published in Tuesday's edition of the Proceedings of the National Academy of Sciences journal.

It has long been known that some of the carbon dioxide (CO2) emitted by human activities stays in the atmosphere for thousands of years, but the new study advances the understanding of how this affects the climate system.

The paper describes what will happen if the atmospheric concentration of CO2 reaches 450-600 parts per million (ppm), up from 385 ppm today. Most climate researchers consider 450 ppm virtually inevitable and 600 ppm difficult to avoid by 2050 if the use of fossil fuels continues at the present rate.

The authors found that the scientific evidence was strong enough to quantify some irreversible climate impacts, including rainfall changes in certain key regions, and sea level rises.

"Our study convinced us that current choices regarding carbon dioxide emissions will have legacies that will irreversibly change the planet," said the report's lead author, Susan Solomon, from the US National Oceanic and Atmospheric Administration.

Dust Bowl

The study showed that if CO2 was allowed to peak at 450-600 ppm, the results would include persistent decreases in dry-season rainfall comparable to that experienced in the 1930s North American Dust Bowl in zones including southern Europe, southwestern North America and western Australia.

The researchers say the oceans are currently slowing down global warming by absorbing heat, but will eventually release that heat back into the air.

And increases in CO2 that occur in this century "lock in" sea level rises that would slowly follow in the next 1,000 years, they state.

Looking at just the expansion of warming ocean waters - without melting glaciers and polar ice sheets - the authors found that the irreversible global average sea level rise by the year 3000 would be at least 1.3–3.2 feet (0.4–1.0 metres) if CO2 peaked at 600 ppm, and double that amount if CO2 peaked at 1,000 ppm.

Not too late

"I don't think that the very long time scale of the persistence of these effects has been understood," said Solomon.

But it was wrong to view the report as evidence that it was already too late to do much good by reducing carbon emissions, she added.

"You have to think of this stuff as being more like nuclear waste than acid rain," said Solomon. "So if we slow it down we have more time to find solutions."

"We need to act now," added Plattner. "Waiting for another ten years means we add another ten years of carbon emissions. The higher the carbon emissions the larger the irreversible fraction of climate change we'll see in the future."

Some climate specialists welcomed the new study.

The new analysis showed that "some dangerous consequences could be triggered and persist for a long, long time, even if emissions were cut radically", Michael Oppenheimer, a geoscientist at Princetown University, told the New York Times.

"It's not like air pollution where, if we turn off a smokestack, in a few days the air is clear," Alan Robock, of the Center for Environmental Prediction at Rutgers University, told Associated Press. "It means we have to try even harder to reduce emissions."

Obama's green agenda

The team's conclusions come as President Obama made his opening move towards a green shift in America's economy.

On Monday the US state department named Todd Stern, a former Clinton administration official who played a key role in the Kyoto negotiations, as its envoy on climate change.

Obama also ordered the Environmental Protection Agency to reconsider its refusal to allow California and more than a dozen other states to impose stricter controls on emissions from new cars and trucks. He followed up by raising fuel efficiency standards on all cars and light trucks rolling off the assembly line from 2011 onwards.

"Amidst the array of challenges facing his administration, President Obama's actions today send a clear signal to America and the world that his administration will play a leadership role on energy and global warming," said Phyllis Cuttino, director of the Pew Environment Group's global warming campaign.

swissinfo, Simon Bradley

Key facts

Temperatures in Switzerland have risen by an average of 0.57 degrees Celsius each decade since 1970. The increase is twice as much as the average for the northern hemisphere.
Carbon dioxide is one of the major gases responsible for the greenhouse effect and global warming. In Switzerland it represents around 80% of harmful emissions. Other gases include methane, nitrous oxide and hydrocarbons.
Despite ambitious emission targets, greenhouse gas emissions have actually risen by 0.4% in Switzerland since 1990.

End of insertion

Switzerland and Kyoto

Kyoto, a 178-nation accord, is a 1997 annex to the 1992 UN climate treaty that requires 37 industrial nations to reduce greenhouse gas emissions by an average of 5% below 1990 levels by 2010.

The Swiss parliament ratified the Kyoto Protocol on climate change in 2003. Switzerland undertook to reduce its CO2 emissions to 10% less than 1990 levels by 2010.

Despite ambitious emission targets, greenhouse gas emissions have actually risen by 0.4% in Switzerland since 1990.

A CO2 law came into force in 2000 to ensure that the Kyoto target was achieved. About a thousand enterprises have taken voluntary measures to reduce their emissions.

But it became clear by 2005 that these measures were not sufficient. It is proving difficult, however, to agree on how to strengthen them.

End of insertion

Articles in this story

In compliance with the JTI standards

In compliance with the JTI standards

More: SWI certified by the Journalism Trust Initiative

You can find an overview of ongoing debates with our journalists here. Please join us!

If you want to start a conversation about a topic raised in this article or want to report factual errors, email us at

Sort by

Change your password

Do you really want to delete your profile?

Your subscription could not be saved. Please try again.
Almost finished... We need to confirm your email address. To complete the subscription process, please click the link in the email we just sent you.

Discover our weekly must-reads for free!

Sign up to get our top stories straight into your mailbox.

The SBC Privacy Policy provides additional information on how your data is processed.