地球的碳预算只有一半大的第一个念头

从化石燃料生产电力的时代可能即将结束。 图片来源:Flickr的菲利普·米尔恩从化石燃料生产电力的时代可能即将结束。 图片来源:Flickr的菲利普·米尔恩

化石燃料的使用将有两倍的速度下降,因为预测,如果全球变暖是要保持2°国际公认的作为是不归路C点范围内,研究人员说。

Climate scientists have bad news for governments, energy companies, motorists, passengers and citizens everywhere in the world: to contain global warming to the limits agreed by 195 nations in Parislast December, they will have to cut fossil fuel combustion at an even faster rate than anybody had predicted.

Joeri Rogelj, research scholar at the International Institute for Applied Systems Analysis in Austria, and European and Canadian colleagues propose in 自然气候变化that all previous estimates of the quantities of carbon dioxide that can be released into the atmosphere before the thermometer rises to potentially catastrophic levels are too generous.

Instead of a range of permissible emissions estimates that ranged up to 2,390 billion tons from 2015 onwards, the very most humans could release would be 1,240 billion tons.

Available levels

In effect, that halves the levels of diesel and petrol available for petrol tanks, coal for power stations, and natural gas for central heating and cooking available to humankind before the global average temperature – already 1°C higher than it was at the start of the Industrial Revolution – reaches the notional 2°C mark long agreed internationally as being the point of no return for the planet.

事实上,在 UN Framework Convention on Climate Change summit in Paris agreed a target “well below” 2°C, in recognition of ominous projections − one of which was that, at such planetary temperatures, sea levels would rise high enough to submerge several small island states.

The Nature Climate Change paper is a restatement of a problem that has been clear for decades. Carbon dioxide proportions in the atmosphere are linked to planetary surface temperatures and, as they rise, so does average temperature. For most of human history, these proportions oscillated around 280 parts per million.

The global exploitation, on a massive scale, of fossil fuels drove the expansion of agriculture, the growth of economies, a sevenfold growth in human population, a sea level rise of 14cms, and a temperature rise of, so far, 1°C.

To stop temperatures increasing another 3°C or more and sea levels rising by more than a metre, humans have to reduce fossil fuel emissions. By how much these must be reduced is difficult to calculate.

“We have been overestimating the budget by 50 to more than 200%. At the high end, this is a difference of more than 1,000 billion tons of carbon dioxide”

全球碳预算 is really the balance between what animals emit – in this context, the word animals includes humans with cars and aeroplanes and factories – and what plants and algae can absorb. So the calculations are bedevilled by uncertainties about forests, grasslands and oceans.

To make things simpler, climate scientists translate the target into the billions of tons of carbon dioxide that, ideally, may be released into the atmosphere from 2015 onwards. Even these, however, are estimates.

There is general agreement that a limit of 590 billion tons would safely keep the world from overheating in ways that would impose ever greater strains on human society. The argument is about the upper limit of such estimates.

Dr Rogelj says: “In order to have a reasonable chance of keeping global warming below 2°C, we can only emit a certain amount of carbon dioxide, ever. That’s our carbon budget.

“This has been understood for about a decade, and the physics behind this concept are well understood, but many different factors can lead to carbon budgets that are either slightly smaller or slightly larger. We wanted to understand these differences, and to provide clarity on the issue for policy-makers and the public.

“This study shows that, in some cases, we have been overestimating the budget by 50 to more than 200%. At the high end, this is a difference of more than 1,000 billion tons of carbon dioxide.”

The same study takes a closer look at why estimates of the “safe” level of emissions have varied so widely.

One complicating factor has been, of course, uncertainty about what humans might do, and another has been about the other more transient greenhouse gases, such as methane and the oxides of nitrogen.

Although short-lived and released in smaller quantities, some of these are potentially far more potent than carbon dioxide as an influence on planetary temperatures.

Complex calculations

But Dr Rogelj and his colleagues found that a significant cause of variation was simply a consequence of the different assumptions and methodologies inherent in such complex calculations.

So the researchers have re-examined both the options and the approaches, and have worked out a global figure that, they suggest, could be relevant to “real-world policy”.

It takes into account the consequences of all human activity, and it embraces detailed outlines of possible low-carbon choices. It also offers, they say, a 66% chance of staying within the internationally-agreed limit.

“We now better understand the carbon budget for keeping global warming below 2°C,” Dr Rogelj says. “This carbon budget is very important to know because it defines how much carbon dioxide we are allowed to release into the atmosphere, ever.

“We have figured out that this budget is at the low end of what studies indicated before, and if we don’t start reducing our emissions immediately, we will blow it in a few decades.” – 气候新闻网

作者简介

蒂姆·雷德福,自由撰稿人蒂姆·雷德福是一个自由撰稿人。 他工作了 “卫报” 对于32年,成为(除其他事项外)的信件编辑,美术编辑,文学编辑和科学编辑。 他赢得了 英国科学作家协会协会 奖每年四次的科普作家。 他曾在英国委员会为 减少自然灾害国际十年。 他演讲了关于科学和几十个英国和外国城市的媒体。

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科学改变世界:其他1960s革命的不为人知的故事
蒂姆·雷德福.

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