Man-made climate change could turn Antarctica green, with plants colonizing the land as ice sheets shrink, scientists have warned.

Experts believe clues about the future of the planet can be gleaned from the Pliocene period 3 million years ago, the last time carbon dioxide levels in the atmosphere were as high as they are today.

Carbon dioxide levels in the atmosphere reached 400 parts per million (ppm) on average in 2015 for the first time since records began, World Meteorological Organization figures show.

There is likely to be a “lag” before the true effects of reaching such a threshold are felt, said Professor Martin Siegert, co-director of the Grantham Institute at Imperial College.

However, he added, looking to the Pliocene era could offer clues as to how humans might deal with the challenges this creates.

During that period, sea levels were around 15 meters higher and temperature estimated to be between 2 and 3.5 degrees Celsius warmer than now. “[If] you put your oven on at home, and set it to 200 degrees Celsius, the temperature doesn’t get to that immediately,” Siegert said. “It takes a bit of time, and it’s the same with the climate.”

Professor Dame Jane Francis, director of the British Antarctic Survey, said remnants of the forests of Antarctica have been found, which are probably dated to the Pliocene age.

“The really important significance of this is that we’ve got 400 ppm now, and if we had 400 ppm in the past, this is maybe where we are going back to,” she said. “Which is the ice sheets are going to shrink at times, not all the time but at times... which may allow plants to colonize in Antarctic land again.”

Before the industrial revolution in 1850 carbon dioxide levels were about 280 ppm, and since then the temperature has increased globally by around 1 degree Celsius, Siegert added.

“What it means is that by the end of this century, we might expect another 1 degree,” he said.

If carbon dioxide emissions continue at current rates, levels could soar to 1,000 ppm by 2100, he added. This is the same as estimated levels around 100 million years ago, when dinosaurs roamed the earth and Antarctica was warmer and much greener.

Words to Learn 相关词汇

【搜集】sōují glean gather information or material bit by bit

【游荡】yóudàng roam travel through a wide area

科学家警告说，人为的气候变化可能会让南极洲“变绿”，随着冰川消退，南极洲大陆上将会被植被覆盖。

专家认为，地球未来演变的趋势可以从300万年前的上新世时期找到线索，当时地球大气中的二氧化碳水平和现在一样高。

世界气象组织的数据显示，2015年大气中的二氧化碳平均水平达到了百万分之400，是有记录以来的最高水平。

帝国理工学院格兰瑟姆研究所的联合主任马丁•西格特说，人们对达到这样一个临界点的真实后果的感知会有一个“滞后期”。

但是他补充说，人类要如何应对二氧化碳水平过高带来的挑战，可以从上新世时期找到线索。在这一时期，海平面上升了约15米，温度比现在高出2到3.5摄氏度。

西格特教授说：“如果你在家里打开炉子，把温度调到200度，不会立刻达到这一温度。这需要一段时间，气候也是一样。”

英国南极观测站的站长德蒙•简•弗朗西斯教授说，南极洲森林遗迹已经被找到，这些森林很可能来自上新世时期。

她说：“这些森林遗迹之所以非常重要，是因为我们现在的二氧化碳水平已经达到百万分之400，如果过去地球的二氧化碳水平也曾经达到百万分之400，这也许就是地球将回归的状态。冰川时不时地会消退，不是一直消退而是偶尔消退，这可能会让植被重新覆盖南极洲大陆。”

西格特教授补充说，在1850年工业革命之前，二氧化碳水平约为百万分之280，自那以后全球温度上升了约1摄氏度。

他说：“这意味着到本世纪末，全球温度将再上升1摄氏度。”

他还说，如果二氧化碳排放量以目前速度持续下去，到2100年，大气中的二氧化碳水平将高达百万分之1000。

届时二氧化碳水平将和1亿年前持平，那时候的地球恐龙横行，南极洲比现在更温暖，也绿得多。(Chinadaily.com.cn)