Climate change

【导读】：近些年，随着气候变暖，极端天气的发生越加频繁。

美国戈达德太空研究所的负责人汉森博士被尊为“气候变暖研究之父”，他与他的同事将一起揭晓六十年来气候变暖到底有多严重。

Climate change气候变化Bell weather呈“钟形曲线”变化的天气A statistical analysis shows how things really are heating up一项统计分析显示出天气究竟是如何变热的Aug 11th 2012 | from the print editionARE heatwaves more common than they used to be? That is the question addressed by James Hansen and his colleagues in a paper just published in the Proceedings of the National Academy of Sciences. Their conclusion is that they are—and the data they draw on do not even include the current scorcher that is drying up much of North America and threatening its harvest. The team’s method of presentation, however, has caused a stir among those who feel that scientific papers should be dispassionate in their delivery of the evidence. For the paper, interesting though the evidence it delivers is, is far fromdispassionate.热浪来袭真的比以前更加频繁了吗？詹姆斯•汉森①与他的同事试图在《美国国家科学院院报》上发表的一篇新文章中回答这一问题。

他们得出的结论是，情况的确如此，而且得出这一结论的依据这还不包括最近北美的酷热天气。

现在那里的大部分地区已经干旱无比，当地农作物的收成也因此受到了威胁。

然而，詹姆斯•汉森与他的同事所采用的展示方案却在一群人中引起了骚动。

这些人认为科技论文在表述证据时应客观公正，但有意思的是，该文章在表述证据时却远未做到不偏不倚。

Dr Hansen, who is head of the Goddard Institute for Space Studies, a branch of NASA that is based in New York, is a polemicist of the risks of man-made global warming. Despite his job running a government laboratory, he has managed to get himself arrested on three occasions for protesting against those he thinks are causing such climate change.He clearly states in the paper’s introduction that he was looking for a way of conveying his fears to a sceptical public.总部在纽约的戈达德太空研究所(GISS)②是美国国家航空航天局的一个分支部门，该研究所的负责人汉森博士能言善辩，他声称人为因素导致的全球变暖将给人类带来危害。

尽管汉森博士主管政府实验室，他却参加过抗议活动，以此来反对那些他认为将造成此类气候变化的行为，而他也因此“如愿”被警察逮捕过三次。

汉森博士在他的文章序言中明确指出，他正在寻找一种方法，以此让那些对他的观点持怀疑态度的公众体会到他的焦虑。

Some of that scepticism is connected with the fact that although changes in the climate will inev itably result in changes in the weather, ascribing any given event—such as a local heatwave—to climate change is impossible. Dr Hansen has therefore tried to go beyond the study of individual causes by demonstrating that what was once unusual is now common.尽管气候变化将不可避免地导致天气变化，但不能将所有特定事件（如地方性的热浪）都归因于气候变化，而公众的怀疑态度中有一部分就与这一事实有关。

因此，汉森博士通过论证过去人们眼中的异常天气如今已是十分常见，试图使他的研究不仅仅局限于个别原因。

Longer, hotter summers夏天愈加漫长炎热了To do so, he and his colleagues took 60 years’ worth of data (the period from 1951 to 2011) from the Goddard Institute’s surface air-temperature analysis. This analysis divides the planet’s surface into cells250km(about 150 miles) across and records the average temperature in each cell. The researchers broke their data into six decade-long blocks and compared those blocks’ statistical properties.为此，汉森博士与其同事从戈达德研究所收集了60年（从1951年至2011年）地表气温分析数据。

这些分析材料将地球表面分成了一个个宽250公里（约150英里）的区块，并记录了每个区域内的平均温度。

研究者将这些数据按十年一组分成了六个时间段，并对这些时间段内的统计特性进行了比较。

They looked in particular at the three months which constitute summer in the northern hemisphere (June, July and August). First, they created a reference value for each cell. This was its average temperature over those three months from 1951-80. Then they calculated how much the temperature in each cell deviated from the cell’s reference value in any given summer. That done, they plotted a series of curves, one for each decade, that showed how frequently each deviant value occurred.研究者特别关注了北半球夏季三个月（六月、七月、八月）的温度。

首先，他们计算出了1951年至1980年每一个区块夏季三个月的平均温度，并将这些数据作为每个区块的参考值。

接着，研究者又计算在任意指定的夏季内每个区块内的温度分别与各自的参考值存在多少偏差。

这一步完成后，他们以十年为单位绘制了六条曲线，这些曲线显示出了每一个偏差值发生的频率。

Since small deviations are common and large ones are rare, the result of plotting data in this way is a curve shaped somewhat like the cross-section of a bell. Such distributions can be modelled by a mathematical function known as the normal distribution—or “bell curve”.由于小的偏差时有发生，而大的偏差则较为少见，因此用这一方法对数据进行描绘，得出的曲线形状就像一个钟的横截面。

这样的分布状态可以用数学上的一个函数来表示，即正态分布，又称“钟形曲线”③。

Whether based on data or a mathematical ideal, such a curve always has two parameters. These are its mean (the value of all of the data points added together and div ided by the number of points; this is also the peak of an ideal curve) and its standard deviation, which measures how wide the bell is. The standard deviation is calculated from all of the individual deviations of the data points.无论是基于数据还是理想数学模型，钟形曲线都有两个参数。

一个是平均值（将所有数据的值相加，除以总数所得；同时也是这条理想曲线峰值的横坐标值），另一个是它的标准差④（代表钟形曲线的“胖瘦”）。

标准差可以通过计算所有数值的方差（再开方）得到。

To see what was going on, Dr Hansen superimposed the actual curves for each decade from the fifties to the noughties on a normal distribution, which acted as a reference curve. To make all the curves comparable, he expressed the values of the actual deviations as fractions of a standard deviation, and their frequencies as proportions of their total number.为了弄清气候变化，汉森博士以正态分布曲线为参照曲线，将其与六十年中每十年一条的实际曲线相叠加。