Steep emissions cuts take a chunk of warming with them – study

The Grangemouth Refinery in England. Scientists say society must cut its use of carbon-intensive fossil fuel by 70 percent this century to avoid the most dangerous aspects of climate change. Photo by Sebastien Krebs, flickr.

14 April 2009 (UPDATED 4:30 pm EDT)

But "we can no longer avoid significant warming during this century," lead scientist warns.

By Douglas Fischer
Daily Climate editor

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

And that’s the good news.

Because a 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 society's fossil-fuel-based economy and an unprecedented level of global cooperation.

That major effort to slash emissions, the scientists warned on Wednesday, 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’re on a very dangerous path," said NCAR senior scientist Warren Washington, the lead author. "We can no longer avoid significant warming during this century."

But "we could stabilize the threat of climate change and avoid catastrophe."

The study, employing the latest-generation computer models, is one of the first to assess different scenarios, or storylines, and the effects different efforts to stem warming will have on the future climate. It will be published next week in the journal Geophysical Research Letters.

"The absolute numbers that come out" – be it a temperature increase of 1.5 degrees or an eight- or nine-inch sea-level rise – "may not be the exact things we’re going to see," said Claudia Tebaldi, a study co-author and a statistician with Climate Central, a science and media nonprofit dedicated to improving information on climate change.

"The significance of the difference is important. And that we have a lot of confidence in."

The research suggests that, while the world will see some warming no matter what, prompt action to mitigate emissions can blunt the most dangerous disruptions:

• 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.

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

Global average temperatures would still rise by nearly 1º F, about what scientists say the globe has seen 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 no matter what happens, they continue to rise beyond 2100, given the oceans’ thermal inertia.

And while a steep 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, absent severe cuts, industrial exhaust will push global temperatures four degrees Fahrenheit above today’s readings – well beyond a mark 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.

But that kind of a levy will be a tough sell: The White House has stepped back from a cap-and-trade emissions limit in its budget proposal, while the G20 world leaders returned earlier this month from an economic summit with no progress to report on emissions.

Indeed, a poll conducted by the London Guardian and published Wednesday exposes that gulf between what scientists and politicians think possible. While world leaders 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 Climate Central, 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."

Contact Daily Climate editor Douglas Fischer at dfischer@dailyclimate.org

Find more Daily Climate stories in the TDC Newsroom

This work by The Daily Climate is licensed under a Creative Commons Attribution-No Derivative Works 3.0 United States License.

Based on a work at www.dailyclimate.org.