View larger image | New research shows that extreme summer heat, such as the 2010 heat wave that enveloped Moscow in smoke from wildfires (above right), is becoming more common in the Northern Hemisphere. Average summer temperatures in 1951–1980 fell along a bell curve (gray), with as many cooler-than-normal days (blue) as warmer ones (orange). Over time, the distribution of Northern Hemisphere temperatures shifted to the right, or warmer. Scientists use the analogy that the weather dice have become loaded: The odds of hot temperatures in recent years would cover four and a half sides of a six-sided die instead of two sides as before. Credit: Source: GISS/NASA; Photo: Mikhail Metzel/Associated Press