Construction workers in Marseille, Summer 2006.

Claude Paris/AP

Scientists are certain that our globe is warming—because they've been tracking the global average temperature for decades. All told, Earth's average temperature has risen by about 0.8°C (1.4°F) over the past 100 years.

This temperature change may not seem like much, but even small changes can wreak havoc with the conditions around us. And Earth shows no signs of cooling off anytime soon. The temperature rise began around 1910, leveled off in 1940s, and then accelerated in the late 1970s. As of 2007, the years 1998, 2005, and 2007 are the three warmest ever recorded.

IPCC Working Group I Contribution to the Fourth Assessment Report, ch. 3, faq 3.1 p.253

Global mean temperature, 1850-2000.

Is Earth Warming Everywhere?

No. As a whole, Earth is warming, but not all places are heating up at the same rate, as is evident in a map in the exhibition showing regional changes in the average surface air temperature between 1979 and 2005. The Arctic has been warming more than other regions, land areas have been warming more than ocean areas, and a few places are actually cooling.