不同的数据，同样的趋势

英国气象局观测数据

每一年，来自全球几大主要气象研究所——美国国家航天航空局下属的戈达德太空研究所（GISS），美国国家海洋和大气管理局的国家气象数据中心（NCDC），日本气象厅和英国气象局的哈德利气象中心——的科学家们会统计世界各地气象站的数据，独立的得出这一年与之前相比是更温暖了还是更寒冷。

On January 12, 2011, the NASA group announced that 2010 had tied 2005 as the warmest year in their 131-year instrumental record. NOAA also declared 2010 to be tied with 2005. The Japanese Meteorological Agency noted in a preliminary analysis that 2010 was the second warmest. The Met Office Hadley Centre has yet to make its announcement.

2011年1月12日，美国国家航天航空局（NASA）宣布2010年和2005年的一样，是在他们有仪器记录的131年里最温暖的一年。美国国家海洋和大气管理局（NOAA）也宣布2010和2005年温度持平。日本气象厅的初步分析结果是2010年是历史上第二温暖的年份。哈德利气象中心还没有得出结论。

But how much does the ranking of a single year matter? Not all that much, said James Hansen, the director of NASA GISS. In his group’s analysis, 2010 differed from 2005 by less than 0.01°C (0.018 °F), a difference so small that the temperatures of the two years are almost indistinguishable, given the uncertainty of the calculation. Meanwhile, the third warmest year, 2009, is so close to 1998, 2002, 2003, 2006, and 2007 (the maximum difference between years is 0.03°C), that all six years are virtually tied.

但是仅一年的排名能说明什么问题呢？并没有太大价值，戈达德太空研究所的主任James Hansen说。在他小组的分析中，2010年的平均气温只比2005年低了不到0.01摄氏度（0.018华氏度），如果考虑到计算统计中的误差，这点相差可以忽略。同时，历史上第三温暖的年份——2009年与1998、2002、2003、2006和2007年的平均气温最大相差只有0.03摄氏度；可以说，这六年的气温实际上是一样的。

What matters more than a yearly record from a single group is the longer trend, as shown in the plot at the top of this page. The four records are unequivocal: the world has warmed since 1880, and the last decade has been the warmest on record.

比研究一年一年的记录更有价值的是研究长期的趋势，正如本文一开始所展示的图表。四个研究所的数据明确的说明了地球从1880年温度开始逐年上升，近十年是记录上最温暖的年份。

When we focus on the annual rankings, the differences between the temperature analyses can be confusing. For example, GISS previously ranked 2005 as the warmest, while the Met Office listed 1998. The discrepancy helped fuel a misconception that findings from the research groups varied sharply or contained large degrees of uncertainty. It also fueled a misconception that global warming had stopped in 1998.

当我们把注意力放在年份的排名上时，数据分析间的不同很让人迷惑。例如GISS之前的记录表明2005年是最温暖的一年，而英国气象局的记录是1998年。这样的分歧加剧了人们对于气象研究数据的误解。他们往往认为不同研究所得研究结果有很大的差别并且有着相当的不确定性。甚至还有人认为全球变暖在1998年就已经停止了。

“The official records vary slightly because of subtle differences in the way we analyze the data,” said Reto Ruedy, one of Hansen’s colleagues at GISS. “But they also agree extraordinarily well.”

“这些官方数据间微小的差别产生的主要原因是数据分析方法间的微妙差别，”Hansen在GISS的同事Reto Ruedy说，“但大体上还是一致的。”

All four records above show peaks and valleys in sync with each other. All show particularly rapid warming in the past few decades. And all show the last decade as the warmest.

以上的四组数据所展示的峰和谷都是一致的。他们都表明温度在最近的几十年中上升的速度很快以及近十年是历史上最温暖的十年。

The small discrepancies between the records are mostly due to the way scientists from each institution handle regions of the world where temperature-monitoring stations are scarce—parts of Africa, Antarctica, the Arctic, and the Amazon. For instance, GISS fills in the gaps (see the first global map above) with data from the nearest land stations. The Met Office analysis (second of the two global maps above) leaves areas of the Arctic Ocean out.

这些数据间的小差异大多是由于不同研究所在处理一些边远地区气候数据的方法不同而导致的。这些地方的气象站很稀少，包括非洲的部分地区、南极洲、北极和亚马逊雨林。例如，GISS记录最近的陆地上的气象站的数据（见第一张世界地图）；英国气象局的数据则未包括北极（见第二张世界地图）

Both approaches pose problems. By not inferring data, the Met Office assumes that the areas without stations have a warming equal to that of the entire Northern Hemisphere—a value that satellite and field measurements suggest is too low, given the observed rate of Arctic sea ice loss. On the other hand, GISS’s approach may either overestimate or underestimate Arctic warming.

这两种方法都有问题。英国气象局的方法是不估测数据，没有气象站的地区用整体北半球的暖化程度来代替。整体北半球的暖化程度是由卫星和地球上的一系列的测量计算出的。这个值往往偏低，因为当中含有北极冰块的消融。另一方面，GISS的方法也不能对北极的暖化程度有一个准确的反映。

“There’s no doubt that estimates of Arctic warming are uncertain, and should be regarded with caution,” Hansen said. “Still, the rapid pace of Arctic ice retreat leaves little question that temperatures in the region are rising fast, perhaps faster than we assume in our analysis.”

“毫无疑问，对于北极暖化得现象的估计是不确定的，所以应该谨慎评估，”Hansen说。“然而，北极冰块融化的速度逐渐加快也表明该地区的温度在迅速升高，速度可能超过我们在分析报告里的假设。”

The temperature records also differ slightly because the point of reference that each group uses to calculate global temperature is different. It is not possible to reliably calculate absolute global average surface temperatures, so scientists instead calculate a relative measure called a “temperature anomaly.” They compare average temperatures at any given time and place to a long-term average, or base period, for each area. GISS uses a base period of 1951 to 1980; the Met Office uses 1961 to 1990; the Japanese Meteorological Agency uses 1971 to 2000; and NCDC uses the entire 20th century.

温度的记录间的细微差别的原因还有一点是不同研究所运用的测量温度的参考不一样。要直接得到真实的全球地表气温是不太可能的，所以科学家们要在计算结果中加入“气候异常”的因素。在每个地区，他们都用一个时间点的平均气温和长期或者一段时间内的平均气温进行比较。GISS用的是1951年到1980年的气温数据；英国气象局用的是1967年到1990年的气温数据；日本气象厅用的是1971到2000年的气温数据；NCDC用得失整个20世纪的气候数据。

This means that numerical values of the temperature anomalies differ. But it does not change the magnitude of temperature changes over the past century.

这意味着：尽管在数字上这些温度反常会不一样，但是上世纪气温变化的总量是不会变化的。

NASA images by Robert Simmon, based on data from the NASA Goddard Institute for Space Studies, NOAA National Climatic Data Center, Met Office Hadley Centre/Climatic Research Unit, and the Japanese Meteorological Agency. Caption by Adam Voiland and Mike Carlowicz.

制图/Robert Simmon

数据来源/NASA Goddard Institute for Space Studies, NOAA National Climatic Data Center, Met Office Hadley Centre/Climatic Research Unit, and the Japanese Meteorological Agency

文字说明/Adam Voiland and Mike Carlowicz