科学美国人60秒 SSS 二氧化碳浓度回到过去水平（在线收听）

Climate 420 Million Years Ago Poised for Comeback 二氧化碳浓度回到过去水平

“We’re hearing a lot of the arguments against action on reducing CO2being based on, ‘well CO2 was higher in the past, so we don’t have to worry about it.’

我们听到很多关于反对减少CO2的争论,”CO2含量本来就很高,我们不用担心.”

Gavin Foster, a geochemist at the University of Southampton. But Foster says that’s a flawed argument. For starters, just how far back in time do you have to look to find CO2 concentrations like what we expect to see in the future, and does it even make sense to compare the levels now and then?

加文·福斯特,是南安普顿大学的地球化学家。但是福斯特表示,这是一个有缺陷的观点.首先,那得追溯到过去什么时候,二氧化碳的浓度才和现在一样高,其次, 将现在二氧化碳的浓度和当时相比有什么意义呢?

To answer these questions, Foster and his colleagues reconstructed the history of atmospheric carbon dioxide for the last 420 million years. They compiled roughly 1,500 estimates of CO2 concentrations from 112 previous studies. When the researchers combined these data, they found that atmospheric carbon dioxide went up and down over time, but that, in general, it gradually declined from almost 3,000 parts per million down to less than 300 parts per million before humans started burning fossil fuels.

为了回答这些问题,福斯特和同事们重构了过去4.2亿万年前大气中二氧化碳的历史.他们对之前关于112个研究中关于二氧化碳浓度的近1500种估计进行了编纂. 研究人员综合这些数据,他们发现,随着时间的推移,大气中的二氧化碳含量也在上下起伏,但是总体而言,在人类开始燃烧矿物燃料之前,大气中的二氧化碳含量从3000ppm下降到了不足300ppm.

However, we have already started to reverse that trend. If we continue on a business-as-usual scenario, by the middle of this century, CO2 could reach levels not seen in 50 million years, according to Foster’s reconstruction. That’s long before humans evolved, back when the climate was much warmer and there were no large ice sheets at the poles. If we continue on that trajectory, by the year 2250, concentrations could approach what they were in the Triassic, 200 million years ago, when dinosaurs roamed the Earth.

但是，现在我们已经开始扭转这一趋势。如果我们继续按照“一切如常”，根据福斯特的数据，到本世纪中叶，二氧化碳的浓度将会突破过去5千万年新高。而在5千万年前，气候还非常的温暖，地球的两极还没有冰原。如果我们继续这种轨迹，那么在2250年，大气中二氧化碳的浓度将会达到2亿年三叠纪时的水平，而那时恐龙还在地球上漫步。

But greenhouse gases aren’t the only factor impacting Earth’s climate. The sun also plays a major role. It’s grown brighter over time, offsetting most of the cooling related to dropping CO2 levels, Foster’s team found. And that fact has important implications for modern climate change. Because while we’re headed toward a world with CO2 levels similar to what they were in the distant geologic past, it won’t just be like rewinding the clock.

但是温室气体并不是影响地球气候的唯一因素。太阳也起着重要的作用。福斯特团队发现，随着时间的推移，太阳的亮度增加，这会抵消降低二氧化碳含量的多数冷却成分。这一事实对于现代气候的变化有着重要的意义。因为未来的世界二氧化碳的水平和遥远的地质时代的水平相似，这并不像时间倒流这么简单。

“So, because the sun is now brighter than it was 200 million years ago, or 400 million years ago, that radiative forcing from CO2 in the future is going to be that much more potent. And that, we thought, was quite a strong message that hadn’t been noted before.”

现在与2亿年前相比，或者4亿年前相比，现在的太阳亮度增加了，这会使未来二氧化碳的辐射强度更加强大。我们认为，这是我们之前没有注意到一个强有力的信息。

The findings are published in the journal Nature Communications.

该研究结果发表在《自然通讯》杂志上。

Foster stresses that this isn’t a vision of what will be, but what could be. “It’s more of cautionary note that, in the absence of any action, we will be entering a world quite rapidly—in the next 150 years—where the climate is receiving a magnitude of forcing that, as far as we know, it hasn’t received for 420 million years…it’s outside the bounds at which the Earth is normally functioning. Doesn’t sound like a good place to be to me.”

福斯特强调，这并不是一个愿景，而是未来会实现的。“这更多的是警示，如果不采取任何的行动，在未来150年，我们将迅速进入一个世界——据我们所知，未来气候将达到强迫级别，而在4.2亿年前，也未达到这种情况。表面看来地球运行正常，但是似乎对于我来说，不再像一个完美的地方了。”