Heatwaves and droughts

By studying weather and climate data gathered from all over the world, and transmitted from orbiting satellites, scientists can compare it with past records to work out how much the world has warmed up. But for many people, the evidence of climate change is much more obvious. They are suffering heatwaves that can raise temperatures to lethal levels, and living with droughts that make drinking water scarce, kill their crops and farm animals, and turn fertile land to desert. Some of the droughts may be caused by natural cycles, and deserts can be partly created by poor farming methods such as overgrazing by livestock. But there is little doubt that periods of seriously hot or dry weather are getting more frequent.

HEATWAVES

Higher extreme temperatures are becoming more common. They are not always the highest daytime temperatures known since records began, but long periods of sustained high temperatures known as heatwaves. During the European heatwave of August 2003, Paris suffered nine days in a row with temperatures above 95°F (35°C). Aug 10 of that year was the hottest day ever recorded in London, peaking at 100.6°F (38.1°C), and 117.1°F (47.3°C) was recorded at Amareleja in Portugal. Here a fountain in Prague helps a woman cool down during a heatwave that hit the Czech Republic in July 2007.

THE HUMAN TOLL

Heat can be a killer, especially when it continues through the day and night. In the US, people cope with heat by using air conditioning—which itself contributes to climate change. In regions where people are not equipped to deal with the heat, they are more vulnerable. The elderly are the first to suffer, like this victim of a heatwave in Chicago in 2006, because their bodies cannot lose heat easily. In Rome, Italy, half the city's 700 casualties of the 2003 European heatwave were over 85 years old—and the heat is believed to have killed as many as 50,000 people throughout Europe.

1973 2001

SHRINKING LAKES

Heat makes water evaporate from the ground surface, drying the soil. If this moisture is not replaced by rainfall, the level of groundwater sinks, draining the water from lakes. People often make the problem worse by diverting water into irrigation schemes designed to revive wilting crops. Over the last 40 years, a combination of these factors has caused the near-disappearance of Lake Chad on the southern fringes of the Sahara. The lake is seen here in two satellite views taken 26 years apart. Once the sixth-largest lake in the world, it is now one twentieth of its original size.

DESERTIFICATION

If there is not enough rain to make up for the evaporation of water from the ground, the soil can gradually turn to dust. This process can be accelerated or even caused by poor farming methods, as happened in the Great Plains states in the 1930s, or more recently in the Sahel region on the southern fringes of the Sahara in Africa. But if rainfall dwindles to below the critical level, even well-managed land will turn to desert. This may be happening in eastern and southeastern Australia, where the rainfall of 2006 was among the lowest on record. Low rainfall is also causing the expansion of the central Asian Gobi Desert, driving dust storms across huge areas of China and Mongolia. This Mongolian woman is carrying water to her home during one of the dust storms.

Scarf protects the woman from airborne dust during the storm

Scarf protects the woman from airborne dust during the storm

DRIED-UP RIVERS

Reduced rainfall is making some rivers dry up. In 2005 they included the greatest river of all, the Amazon, which suffered its worst drought in 40 years. Many of its tributaries shrank to a fraction of their normal width, exposing broad areas of dried, cracked mud littered with dead fish. The Rio Negro, the main northern tributary of the Amazon, was reduced to its lowest level since records began in 1902.

DROUGHT AND FAMINE

Many people who live on the dry fringes of deserts rely on seasonal rains to make their crops grow and provide water for their farm animals. If these rains fail owing to changed weather patterns, the crops and animals may die, as seen here in southern Ethiopia in 2006. This leaves the people with nothing to eat, and facing the threat of famine.

WILDFIRES

The firefighters on top of this house are desperately trying to save it from a forest fire that ignited during very hot and dry weather. In dry regions such as Australia, many plants are able to cope with regular fires, but during long droughts, the risk of fire can spread to areas where the vegetation is not adapted to survive it. In parts of Amazonia, a combination of drought and deforestation is making the ground so dry that wildfires are raging through forests that have never suffered them before.

Melting ice

Melting ice

In cold climates snow builds up and gradually become compacted into virtually solid ic forming mountain glaciers and polar ice sheets. Polar oceans al; freeze at the surface in winter, creating floating pack ice. But a of this ice is melting. Arctic pad ice is shrinking, vast Antarctic ice shelves are collapsing, and mountain glaciers are retreating On the polar fringes, higher temperatures are also melting ice that lies beneath the ground transforming tundra landscapes

Ice acts like a mirror, reflecting solar energy

Dark water absorbs energy and gets warmer

ACCELERATING THE MELT

Glittering white sea ice reflects most of the Sun's energy. But if it melts, it gives way to dark ocean water, which absorbs most of the energy and warms up, melting more ice. This positive feedback effect is probably increasing the rate of Arctic sea ice melting.

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ICELAND

States, Halt ot this area melts in summer, leaving the central Arctic Ocean still icy. Since 1979 the size of this summer ice sheet has dwindled by about 600,000 sq miles (1.5 million sq km)—an area about twice the size of Texas. During the 1990s its average thickness also decreased by 3 ft 4 in (1 m).

GREENLAND

Most of Greenland is covered by a huge ice sheet, more than 1.9 miles (3 km) thick at its center. Every summer the edges of the ice get thinner, and the area affected by this is increasing. The glaciers that flow from the ice sheet to the sea are also moving faster, increasing the rate at which icebergs break away and melt. Both of these processes are causing the sea level to rise.

Iceberg has broken off floating edge of ice sheet

Iceberg has broken off floating edge of ice sheet

MELTING PERMAFROST

About a quarter of the land in the Northern Hemisphere is so cold that it is permanently frozen beneath the surface. This permafrost is covered by a surface layer that is frozen in winter but thaws in summer, creating vast areas of swampland. In many areas of the lower Arctic, the active surface layer is getting deeper each year, melting ancient ice and undermining buildings like this house in Irkutsk, Siberia, which is slowly sinking into the ground.

RETREATING GLACIERS

Glaciers form as snow builds up over the years, packing down to form rivers of ice that creep slowly downhill, scouring deep U-shaped valleys. In the polar regions, many glaciers flow all the way to the sea, where ice breaks off to form icebergs. But most glaciers that form in high, cold mountain valleys turn to streams and lakes of meltwater long before they reach the coast. All over the world, rising temperatures are making these mountain glaciers melt away at their lower, warmer ends, which retreat uphill to where temperatures are lower. The retreat can be dramatic, as shown by these two images of the Upsala glacier in Patagonia, South America—the upper photograph was taken in 1928, and the lower one in 2004.

ANTARCTICA

Antarctica is covered by a colossal ice sheet up to 2.8 miles /ering an area of 5.4 million sq miles :onsists of the huge east Antarctic ransantarctic Mountains, which ■e, and the smaller west Antarctic ice I ice.The ice is melting fastest on isula, where temperatures are rising n anywhere else on Earth, by up to :e 1951.

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was found nearby. But all the ice in the spot where he was found has now melted.

PSING ICE SHELVES

_ 2002, 1,250 sq miles (3,250 sq km) of the 650-ft (200-m) thick Larsen-B ice shelf near the tip of the Antarctic Peninsula disintegrated within 35 days, and the fragments drifted away as icebergs. These satellite images show blue pools of meltwater forming on the surface on January 31 (top), and the ice shelf collapsing 23 days later.

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