National Geographic : 2012 Sep
Something else is happening too: e Earth is steadily getting warmer, with signi cantly more moisture in the atmosphere. Decades of observa- tions from the summit of Mauna Loa in Hawaii, as well as from thousands of other weather sta- tions, satellites, ships, buoys, deep-ocean probes, and balloons, show that a long-term buildup of greenhouse gases in the atmosphere is trapping heat and warming up the land, oceans, and at- mosphere. Although some places, notably the Arctic, are warming faster than others, the aver- age surface temperature worldwide has risen nearly one degree Fahrenheit in the past four decades. In 2010 it reached 58.12°F, tying the record set in 2005. As the oceans warm, they're giving o more water vapor. "Everybody knows that if you turn up the re on your stove, you evaporate the water in a pot more rapidly," says Jay Gulledge, senior scientist at the Center for Climate and Energy Solutions (C2ES), a think tank in Arlington, Virginia. During the past 25 years satellites have measured a 4 percent average rise in water va- por in the air column. e more water vapor, the greater the potential for intense rainfalls. By the end of the century the average world temperature could rise anywhere from three to eight degrees Fahrenheit---depending in part on how much carbon we emit between now and then. Scientists expect the weather to change substantially. Basic circulation patterns will move toward the Poles, just as some plants and animals are doing as they ee (or take advantage of) the expanding heat. e tropical rain belt is already widening, climatologists report. e subtropical dry zones are being pushed poleward, into re- gions such as the American Southwest, southern Australia, and southern Europe, making these regions increasingly susceptible to prolonged and intense droughts. Beyond the subtropics, in the midlatitudes, including the lower 48 of the United States, storm tracks are moving poleward too---a long-term trend superimposed on the year-to-year uctuations triggered by La Niña or El Niño. One of the biggest wild cards in our weather future is the Arctic Ocean, which has lost 40 WHY SO WILD? The atmosphere is getting warmer and wetter. Those two trends, which are clear in data averaged globally and annually, are increasing the chances of heat waves, heavy rains, and perhaps other extreme weather. GRAPHS ABOVE ARE SMOOTHED USING A TEN YEAR MOVING AVERAGE. *AVERAGE TEMPERATURE OVER LAND AND OCEAN JOHN TOMANIO, NGM STAFF; ROBERT THOMASON SOURCES: JEFF MASTERS, WEATHER UNDERGROUND; NATIONAL CLIMATIC DATA CENTER TEMPERATURE, HEAT WAVES, AND RAINFALL ; NOAA HUMIDITY +0.9° 0.1° 1.0° 1920 2010 1970 10.6 10.2 1957 2010 1970 +4% 4% 35% 1920 2010 1970 +31% 9% 16% 2010 1970 1920 +7% Global temperature* deviation from 20th-century average Percentage of U.S. experiencing summer minimum temperatures much above normal Average global specific humidity at sea level Percentage of U.S. getting an elevated portion of precipitation from extreme events AIR TEMPERATURE at Earth's surface has increased 0.9 degree Fahrenheit since 1970. MOISTURE has risen about 4 percent since 1970, according to satellite data. HEAT WAVES of which nighttime lows are one indicator--- are striking a growing portion of the U.S. EXTREME RAINFALLS are now affecting larger areas of the U.S. as well.