Scientists refute argument of climate skeptics.

From Science Daily:

Scientists at the GKSS Research Centre of Geesthacht and the University of Bern have investigated the frequency of warmer than average years between 1880 and 2006 for the first time. The result: the observed increase of warm years after 1990 is not a statistical accident.

Between 1880 and 2006 the average global annual temperature was about 15°C. However, in the years after 1990 the frequency of years when this average value was exceeded increased.

[...] With the help of the so called "Monte-Carlo-Simulation“ the coastal researchers Dr. Eduardo Zorita and Professor Hans von Storch at the GKSS-Research Centre together with Professor Thomas Stocker from the University of Bern estimated that it is extremely unlikely that the frequency of warm record years after 1990 could be an accident and concluded that it is rather influenced by a external driver.

The fact that the 13 warmest years since 1880 could have occurred by accident after 1990 corresponds to a likelihood of no more than 1:10,000.