For the second time in a month, an intense heat wave has hit Western Europe, particularly France. In Toulouse, temperatures reached 90 degrees Fahrenheit by 10 p.m. This heat wave is characterized by unusually high temperatures at night. Alain Pitton/NurPhoto via Getty Images hide caption
Earth's long-term warming, compared against a base line average from 1951 to 1980, can be seen in this visualization of NASA's global temperature record. Kathryn Mersmann/NASA's Scientific Visualization Studio hide caption
A fully loaded container ship sails along the coast. Historically, ships have taken most of the sea measurements that go into the estimate of Earth's average surface temperature. iStockphoto hide caption
Icebergs float in Iceland's Jökulsárlón glacial lake, where the Vatnajökull glacier is retreating quickly due to global warming. iStockphoto hide caption