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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



FLICRK/JOHNLEGEAR

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.

Those models do suggest that failure to stem industrial exhaust will push global temperatures four degrees Fahrenheit above today's readings – well beyond a threshold many scientists fear will produce dreadful consequences. Sea levels under such a scenario rise at least nine inches - likely more – by century's end. Massive ice sheets are destabilized. The Arctic, hit the hardest, would undergo dramatic change.

"We are now completely in charge," said NASA scientist James Hansen, who was not a part of the study but who first urged Congress to stem emissions in 1988.

"We are going to determine the climate for our children and grandchildren. We're much more powerful than the natural forces.... We could be sending the planet back toward an ice-free state."

Hansen and others argue that the only way to avoid such a fate is to slap carbon-based fuels with a significant tax - $115 per ton of carbon dioxide emitted, or about $1 extra on each gallon of gasoline - as well as a heavy push into renewable and nuclear fuels.

A poll conducted by the London Guardian and published today exposes that gulf between what scientists and politicians think possible. While world leaders – and this NCAR study – suggest prompt action can still avert the worst consequences, a majority of scientists polled at a major international conference last month told the paper they fear society is incapable of such action and faces dangerous warming.

The NCAR study, whose authors also hailed from the Institute for Atmospheric and Climate Science in Zurich and from Climate Central, a website founded by NOAA Administrator Jane Lubchenco, took no sides in that debate.

The scenarios, the authors state, should be seen as "storylines" illustrating the outcomes of different choices. "It is clear that emissions reductions in the 21st century need to be large," they said.

"We do not claim they are necessarily politically or economically feasible.... The aim is to provide policy-relevant information for a range of options."

Douglas Fischer is editor of the Daily Climate. This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.

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