Even Deep Cuts in Greenhouse Gas Emissions Will Not Stop Global Warming

Drastic emissions cuts won't stop the global warming from gases already in the atmosphere
Douglas Fischer, Scientific American 14 Apr 09;

BOULDER – Drastic, economy-changing cuts to greenhouse gas emissions will spare the planet half the trauma expected over the next century as the Earth warms.

And that's the good news.

Because failure to significantly curb these planet-warming gases will truly transform our world in less than 100 years.

A new study to be published by scientists at the National Center for Atmospheric Research finds that a 70 percent cut in emissions should stabilize temperatures at a mark not too much higher than today.

Such a cut, most experts agree, would require vast retooling of a fossil-fuel-based economy and an unprecedented level of global cooperation.

But that major effort to slash emissions, the scientists warn, won't stop global warming. The question confronting politicians throughout the world, in other words, is not whether they want the planet to warm: It is to what degree.

"We can no longer avoid significant warming during this century," NCAR scientist Warren Washington, the lead author, said in a statement. But "we could stabilize the threat of climate change and avoid catastrophe."

The study, employing the latest-generation computer models, will be published next week in the journal Geophysical Research Letters. Mitigating emissions, the authors reported, blunts projected climate impacts and avoids the most dangerous potential impacts of climate disruption:

*The late-summer polar ice cap, already at historic lows today, would shrink only another quarter and hold steady by century's end, instead of melting by more than three-quarters with no let-up in sight.

*Arctic warming is potentially cut in half, stabilizing the northern Bering Sea and reducing impacts on commercial and subsistence fisheries.

*Regional heat wave intensity also drops by half, with the greatest reduction occurring over the western United States, Canada and most of Europe, Russia and Northern Africa.

*Flooding risk drops in half for the western tropical Pacific, Northeast United States and Canada, eastern Asia and South America.

But the emissions slash will not stem the tide: Global average temperatures would still rise by nearly 1º F, about what scientists attribute to date from industrial emissions since 1900.

Sea levels would creep up nearly six inches as a result of that extra heat, with any additional rise due to melting ice sheets unaccounted for in the study's calculations. And they would keep rising beyond 2100, given the oceans' thermal inertia.

"Note that despite a 70 percent reduction in emissions over the 21st century," the authors write, "there is virtually no cooling."

And while the cut would stabilize atmospheric carbon dioxide levels, it holds them at about 450 parts-per-million, according to the study. That's nearly 20 percent higher than today's concentrations and at or even above a threshold many scientists fear will trigger a series of cascading and transformative catastrophes.

Pre-industrial carbon dioxide levels were 284 ppm. Unchecked, emissions are on track to reach 750 ppm by 2100. Scientists don't even know what that would look like: Assumptions used by the computer models were drawn up before recent large emission increases from China and elsewhere, leaving scientists to conclude that their "business-as-usual" benchmark is a conservative estimate for what might actually happen.

Massive emissions cuts can save Arctic ice: study
Yahoo News 15 Apr 09;

WASHINGTON (AFP) – Cutting greenhouse gases by 70 percent this century would spare the planet the most traumatic effects of climate change, including the massive loss of Arctic sea ice, a study said Tuesday.

Warming in the Arctic would be almost halved, helping preserve fisheries, as well as sea birds and Arctic mammals like polar bears in some regions, including the northern Bering Sea, according to scientists at the National Center for Atmospheric Research (NCAR).

But the massive cuts of greenhouse gas emissions advocated by the researchers would only "stabilize the threat of climate change and avoid catastrophe," said NCAR scientist Warren Washington, the study's lead author.

The cuts would also prevent huge losses of permafrost and a significant rise in the sea level, said the study to be published next week in Geophysical Research Letters.

"This research indicates that we can no longer avoid significant warming during this century," said Washington, who ran a series of global supercomputer studies.

The planet's average temperatures have warmed by nearly one degree Celsius (1.8 degrees Fahrenheit) since the pre-industrial era. Most of the warming is due to emissions from greenhouse gases, chief among them carbon dioxide, the study noted.

Those gases have increased from a pre-industrial level of about 284 parts per million (ppm) in the atmosphere to more than 380 ppm today. Recent studies have found that temperatures would reach the threshold for dangerous climate change if they rise by an additional one degree Celsius.

If carbon dioxide emissions were to plateau and maintained at 450 ppm -- cited as an attainable target by the US Climate Change Science Program if dramatic emissions cuts are enacted -- global temperatures would rise by 0.6 degrees Celsius (one degree Fahrenheit) by the end of the century, the study said.

But if emissions were allowed to continue their current trend, temperatures would rise by almost four times that amount, to 2.2 degrees Celsius (four degrees Fahrenheit).

The researchers pointed to several major benefits from cutting carbon dioxide emissions.

Holding emissions at 450 ppm would translate to sea levels rising by 14 centimeters (5.5 inches) instead of 22 centimeters (8.7 inches) due to thermal expansion.

Arctic ice volume would shrink by almost a quarter in summertime and stabilize by 2100, rather than shrinking at least by three-quarters and continuing to melt.

The researchers also found that the climate system would stabilize by about 2100, rather than continuing to warm.

"This study provides some hope that we can avoid the worst impacts of climate change--if society can cut emissions substantially over the next several decades and continue major cuts through the century," Washington said.

European Union nations have agreed to cut their greenhouse gas emissions by 20 percent by 2020 from 1990 levels, rising to 30 percent if the rest of the developed world -- mainly the United States and Japan -- agrees to follow suit.

During the 2008 US presidential campaign, Barack Obama vowed to match the European Union's mid-century objectives of cutting CO2 emissions by 80 percent.

But as president, Obama has offered a more modest goal for 2020 of returning the United States to 1990 level emissions, a reduction of about 14 percent from current levels.

Obama's promise of a leading US role on climate change broke with his predecessor George W. Bush's stance, which had long frustrated Washington's EU partners.