In March 2001, George W. Bush refused to sign the Kyoto protocol on global warming. The large oil companies who control the American government are apparently more interested in their profits over the next few years than the health of the planet over the next million.

Over the last twenty-five years, there has been a dramatic thinning of the Arctic ice-sheet. According to Drew Rothrock, from the University of Washington, it has dropped from 3.1m in 1976 to 1.8m in the 1990s. It continues to thin at 0.1m per year.

It now covers 6% less area than it did 20 years ago. As a result, polar bears are starving. Ian Stirling, a polar researcher at the Canadian Wildlife Service, has found that polar bears are 80 to 90 Kg lighter than they were 15 years ago.

This is a particular problem for mothers with young cubs because they don't have big enough fat reserves to produce milk. Stirling found that birth rates have dropped by 15% and infant mortality has increased. For each week lost in hunting time because the pack-ice has broken up early, the polar bears lose 10Kg of body weight. Break-up now occurs from two to four weeks earlier than it did 20 years ago.

There are two reasons why the loss of pack-ice is having such a serious effect on the bears. Polar bears eat during the winter, and hibernate through the other nine months of the year. They move to the edge of the pack ice and hunt seals. Over the past three decades, the pack ice has broken up on average three weeks earlier. This means that their hunting season is shorter than before. The bears start their hibernation with smaller fat reserves, and mother bears have fewer cubs.

In addition to this problem, the retreating pack-ice means that there is less food in the entire ecosystem. In the 1970s, a Russian biologist called Melnikov found that the food-chain in the Arctic Ocean starts with algae and zooplankton attached to ice floes. The algae are eaten by arctic cod; these, in turn, are eaten by seabirds, whales and seals. Polar bears feed on the seals.

When Melnikov returned to the area a few years ago he found that the ice had gone, and along with it, the zooplankton and algae. Animals such as bears and seals had moved north with the retreating pack-ice; however, this created a widening gap of open sea which they had to cross.

How can we be sure that high temperatures are to blame? Because cold temperatures have the reverse effect. In 1991 the volcano Mt. Pintubo erupted, throwing particles of dust into the upper atmosphere. The winter that year was particularly severe, and polar bears were especially well-fed and plentiful, since they had an extra month to hunt seals.

According to Harvey Lemelin, the Executive Director of the Churchill Northern Study Centre in Churchill, Manitoba, polar bears are becoming increasingly desperate for food. "[They] now have to be moved from property using everything from dogs to vehicles to cracker shells."

Lemelin says that the number of violent encounters with hungry bears has almost doubled in the past three years. To cope with this, the town council has set up a prison where the bears are incarcerated before being transported away from the town. There are now more bears in the prison than humans. The fate of the polar bears may seem far removed from what is happening elsewhere on Earth. In fact, it is a clue as to what is going to happen next.

In the early days of coal mining, methane explosions used to be a big problem in coal mines. To give them an early warning system, miners imprisoned canaries and took them down the shaft. Canaries can detect methane before humans can: when they saw the canaries gasping for breath, the miners got out fast.

The polar ice caps are the Earth's early warning system. Like the canaries, they show the first signs of trouble, and tell us when to take action. Our canary is about to keel over.

As the Arctic ice melts, the permafrost will thaw out, releasing yet more carbon dioxide into the atmosphere. Bush has sold his soul to the devil and the rest of us are about to pay the price.