单项选择题

Analysis of ice cores drilled from the glaciers of the Tibetan plateau shows that the region is warmer now than any other time since the so-called "Holocene maximum", between 6,000 and 8,000 years ago. And the temperatures in central China during the past 50 years were a full degree Celsius warmer than those of the previous 50 years. The results are important because computer simulations show that central Asia is likely to be the first place where significant global warming due to the greenhouse effect will show up.
Lonnie Thompson and his colleagues from Ohio State University have been working with researchers from Chinese Academy of Science and the University of Copenhagen. They drilled the ice cores from the large ice cap which lies high on the Tibetan plateau, south of the Gobi desert. The cores provide a record extending back well into the time of the latest ice age, and perhaps beyond 100,000 years ago. Such ice cores yield information about past climates in two ways—from analysis of the varying. dust conrent at different layers in the core, and from measurements of the relative abundance of isotopes (同位素) of oxygen locked up in the molecules of the ice. The amount of dust in the ice depends on how dry the atmosphere was when it was laid down, while the isotopic studies provide a direct measure of the average temperature.
The amount of water evaporating from sea and falling as snow is different for water containing each of the two main oxygen isotopes. The ratio between these depends on temperature in a well-determined way. Using these two lines of attack, Thompson and his colleagues have shown that, in the late stages of the most recent ice age, conditions were colder, wetter and dustier than today. This matches expectations based on the idea that stronger winds blew around an expanded northern ice cap. The new study is very interesting, however. It focuses on the discovery that the past 60 years were at least as warm as any period in the record, with highest values in the 1940s, 1950s and 1980s. Scientists have recently carried out computer simulations which show that the central part of the Asian continent is likely to be one of the regions most strongly affected by the anticipated global warming caused by the greenhouse effect.
In the new study, researchers are interested in the fact that ______.