海洋吸热延缓全球变暖

    有更多证据表明，大气升温的速度明显放缓可能是因为深海吸收了热量。

    在东南亚海域的底部，海水温度正在上升。太平洋一片水域海水温度上升的速度比过去1万年快了至少14倍。这个发现目前仅限于太平洋与印度洋交汇的深海区域，如果这个现象在全球都普遍存在，那么气候变化问题将变得更加紧迫。

    美国新不伦瑞克市罗格斯大学（Rutgers University）的伊尔•罗森塔尔同来自纽约哥伦比亚大学（Columbia University）拉蒙特•多赫帝地球观测实验室（the Lamont-Doherty Earth Observatory）以及麻省伍兹霍尔海洋研究所（the Woods Hole Oceanographic Institution in Massachusetts）的同行们在《科学》（Science）杂志上发表文章称，气象学家们原以为会被大气吸收的热量，很多现在被海洋所吸收，导致深海水温升高。

    过去几年，虽然温室气体排放量有增无减，但全球变暖速度却在放缓。现在有证据显示，温室气体所产生的热量大部分都被海洋吸收、储存起来。

    透明虫外壳中的记录

    不过，现存有关海洋温度的记录少得可怜，人们最多只能找到半个世纪前的记录。罗森塔尔等人于是决定寻找别的可信的方法，他们将目光瞄准了一种古老海洋生物的沉积物。

    一种名为透明虫（Hyalinea balthica）的单细胞生物只生活在500到1000米深的海域。这种生物身上有一层极其微小的外壳，透明虫死后，这层外壳便会沉入海底。构成外壳的原料是溶解于海水中的成分，而各种成分的结构随着海水温度的变化而变化。水温越高，海水中镁元素相对于钙元素的比重就越大，而这种不同被残存的透明虫外壳记录了下来。

    因此，印尼附近的海洋沉积物保存着随时间变化的热量记录。科学家通过研究海洋中心，解读自冰河时代结束以来近1万年的气候变化模式。从海洋沉积物获取的数据印证了一系列已知的气候变化，比如在冰河时代末期曾出现一段很温暖的时期，又比如“中世纪暖期”曾使得葡萄园在英国兴起，再比如在“小冰河期”，伦敦的泰晤士河等河流常常会结冰。

    More evidence has emerged that the apparent slowdown in the rate of atmospheric warming may be explained by heat absorption in the deep ocean.

    Far below the surface, the waters of south-east Asia are heating up. A region of the Pacific is now warming at least 15 times faster than at any time in the last 10,000 years. If this finding – so far limited to the depths where the Pacific and Indian Oceans wash into each other – is true for the blue planet as a whole, then the questions of climate change take on a new urgency.

    Yair Rosenthal of Rutgers University in New Brunswick and colleagues from the Lamont-Doherty Earth Observatory at Columbia University in New York, and at the Woods Hole Oceanographic Institution in Massachusetts, report in the journal Science that deep ocean warming could right now be taking much of the heat that meteorologists had expected to find in the atmosphere.

    In the last few years, even though greenhouse gas levels in the atmosphere have gone up, the rate of increase in global average temperatures has slowed and there is evidence that much of the expected heat is being absorbed by the oceans and carried beneath the surface.

    Record in shells

    But records of ocean temperatures are patchy, and in any case date back only half a century. Rosenthal and his colleagues decided that they could reliably calculate a pattern of temperature changes by looking at a record of deposition through time.

    One little single-celled organism called Hyalinea balthica has evolved to live only at depths of 500 to 1,000 metres. H.balthica makes a microscopic shell, and when it dies, this shell falls to the ocean bottom. It takes the ingredients for the shell from the elements dissolved in the water around it, and the chemical mix available varies with temperature: the warmer the water, the greater the ratio of magnesium to calcium – and this difference is then recorded in the surviving shell.

    So the marine sediments around Indonesia preserve a thermal record of changes with time. The scientists studied ocean cores to “read” a pattern of climate change over the last 10,000 years, since the end of the Ice Age. The readings from the sediments mirror a series of already-known climate shifts – a very warm spell at the end of the Ice Age, a “medieval warm period” when vineyards flourished in Britain, and a “Little Ice Age” when rivers like the Thames of London routinely froze.