氣候之惡兩害相權取其輕----中壢英文補習班－金學堂英語的部落格

【聯合報╱By JUSTIN GILLIS╱陳世欽譯】

Picking the Lesser Of 2 Climate Evils

Climate scientists long ago settled among themselves the question of whether human emissions of greenhouse gases are a problem, concluding that we are running some grave risks. But the field still features vigorous debate about how bad global warming will get, how quickly, and how to combat it.

One fight involves how much effort to put into stopping leaks of methane gas into the atmosphere.

In the United States, some academics complain that President Obama’s plan to make greater use of natural gas, which consists mostly of methane, will lock America into a supposed solution to climate change that will be worse than burning coal.

Is that claim plausible?

The basic scientific facts are pretty clear. By far the most important greenhouse gas that humans are spewing into the atmosphere is carbon dioxide, which comes from burning fossil fuels.

The second most important is methane, which is released when coal is mined; it escapes when wells are drilled for oil or natural gas; and it leaks from pipes that distribute natural gas. Certain agricultural practices also throw up a huge amount Methane is a far more potent greenhouse gas than carbon dioxide. But in stark contrast to CO2, methane breaks down quickly in the atmosphere.

Every time you flip on a light switch, causing more coal to be burned and CO2 to be released, you are slightly altering the earth’s climate for thousands of years. Release a puff of methane, scientists say, and the climate influence will be gone in decades.

“The methane is like a hangover that you can get over if you stop drinking,” said Raymond T. Pierrehumbert, a climate scientist at the University of Chicago .

“CO2 is more like lead poisoning — it sticks around, you don’t get rid of it, and it causes irreversible harm.”

Despite that difference, billions of dollars are being spent to control methane leaks . Dr. Pierrehumbert is challenging that approach. He argues that the world has yet to mount a serious effort to control carbon dioxide, which will be vastly more harmful in the long run, and that methane should be ignored until that bigger problem is fixed.

Scientists taking the opposite view say global warming is already a problem, noting the rise of extreme weather events.

Aggressively controlling methane, they say, would help slow the warming sharply over the coming decades.

By contrast, “our success in controlling CO2 emissions is likely to make very little difference on temperature over the next 40 years,” said Drew Shindell, a NASA climate scientist .

He and other scientists have had some success helping to persuade the United Nations, the United States Department of State and other organizations to back efforts to control the release of methane .

So what has all this got to do with the president’s climate plan? Mr. Obama’s administration intends to cut carbon dioxide emissions from power plants by 30 percent, from 2005 levels, by 2030. That will push states toward much greater use of natural gas to generate electricity — a shift that is seen as combating global warming because, in a power plant, burning natural gas emits roughly half the carbon dioxide as burning coal.

Experts say that it is critical to keep carbon dioxide out of the atmosphere now, even if that requires burning more gas. Dr. Pierrehumbert and Dr. Shindell largely agree on this point .

The larger issue is tough er. If only a limited amount of political capital and money is going to be available to tackle global warming, that would weigh in favor of Dr. Pierrehumbert’s argument for ignoring methane leaks for the time being. Dr. Shindell agrees that methane control should not be pursued at the expense of CO2 control.

But maybe there is a way out of this conundrum.

The idea would be to promise far more aggressive methane control to slow global warming for the benefit of people alive today, along with aggressive CO2 control for the benefit of future generations. If the prospect of near-term climate benefits could spur a notable increase in public support for longer-term measures, too, that would tilt the argument in Dr. Shindell’s favor.

中譯

氣候科學家早就針對人類排放溫室氣體是否造成嚴重問題一事達成共識。他們認為，我們已經面臨某種嚴重的風險。然而科學家對全球暖化究竟會變得多嚴重、速度多快與如何因應的問題，仍有熱烈的辯論。

爭執之一涉及該付出多少努力以阻止甲烷逸入大氣的問題。

天然氣主要的成分是甲烷。美國部分學術界人士指出，歐巴馬總統所提多用天然氣以因應氣候變遷之議，可能產生的後遺症勢必比燃燒煤炭更嚴重。

此說是否有理？

基本的科學事實非常明顯。人類排放的最重要溫室氣體是燃燒化石燃料所產生的二氧化碳，遙遙領先其他氣體。其次是開採煤炭所逸出的甲烷。甲烷會在人類鑿井開採石油或天然氣時逸出，也會自輸送天然氣的管線中逸出。某些農業操作也會產生巨量甲烷。

甲烷是破壞力遠大於二氧化碳的溫室氣體。然而與二氧化碳截然不同的是，甲烷會在大氣中迅速分解。每當你開燈，導致燃燒更多煤炭並釋出更多二氧化碳，無形中就會使氣候輕微改變達數千年之久。科學家說，釋出一陣甲烷，對氣候造成的影響會在數十年內消失。

芝加哥大學氣候科學家皮爾韓伯特說：「甲烷有如一旦你不再飲酒，即可拋開的宿醉。二氧化碳比較像鉛中毒；它會持續存在，你甩不掉它，它會造成無法扭轉的傷害。」

儘管有此差異，各國仍然以數十億美元控制甲烷逸出。皮爾韓伯特博士質疑這種做法。他認為，全球各國對於控制長久而言危害性高出許多的二氧化碳，尚未認真面對，在解決這個更嚴重的問題之前，應暫時擱置甲烷問題。

持相反見解的科學家舉極端氣候事例增加為證指出，全球暖化已經是一個問題。他們說，積極控制甲烷排放可使未來數十年暖化速度大幅減緩。

美國太空總署氣候科學家辛德爾說，相形之下，「我們控制二氧化碳排放的成果，可能無法使未來40年的溫度出現太大差異」。

他與另一些科學家聯手說服聯合國、美國國務院與其他相關組織支持控制甲烷排放的努力，已經取得一定進展。