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IT MAY not be immediately obvious, but the world outside your window is already a changed one. Since the industrial revolution, global temperatures have risen by about 1掳C, which has had an impact at even the largest scales. For example, melting glaciers in Greenland are shifting the distribution of water on Earth, and nudging the planet鈥檚 axis. As a result, the position of the North Pole has moved eastwards by more than 1 metre since 2005. An upshot of this is that Earth will spin faster and, by 2200, days could be 0.12 milliseconds shorter.

Earth鈥檚 tilt is unlikely to affect your life or even that of your children, but other changes are happening closer to home. In the UK, for instance, spring is beginning about two weeks earlier on average than it did half a century ago, and autumn a week later. In the seas, many animals have shifted their range hundreds of kilometres polewards. On land, we are seeing similar shifts, but it can be much harder for terrestrial wildlife to move, not least because of roads and cities.

Another subtle change is that nights are warming faster than days. Night-time is a chance for heat to escape back out into space, but the extra greenhouse gases in the atmosphere are trapping ever more of it. This is particularly bad news during heatwaves: if our bodies don鈥檛 get a chance to cool down at night, it is harder to cope with the heat of the day.

Not only are heatwaves more difficult to deal with in our changing world, they are also more frequent and more extreme. The 2003 European heatwave killed 70,000 people, many of them elderly or young children 鈥� groups who are less able to regulate their core temperature. A 2004 study showed that global warming has at least doubled the risk of such a weather event occurring.

Heatwaves are just one example of extreme weather affected by global warming. Of course, there have always been floods, storms and droughts, but now more rain can fall because a hotter atmosphere can hold more moisture, storms are more violent because there is more energy to power them and droughts can be more severe because water is evaporating faster.

Researchers are working on systems that would give an indication of how likely it is that extreme weather events are a result of climate change, in near-real time. But all weather events are affected to some degree.

Satellite studies show that rising carbon dioxide levels are also making the planet greener, particularly in dry areas. The results are complex, and not always good. In Australia, for instance, the extra vegetation is sucking up more water and reducing river flows by as much as a third.

All the changes due to climate change are overlaid on top of natural swings in the weather and climate, making it difficult to tell what is down to climate change. But long-term studies leave no room for doubt: as temperatures slowly climb, 鈥渘ormal鈥� is a constantly shifting state.听Michael Le Page

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Back to basics: how we know CO₂ is at fault

It makes up just 0.04 per cent of the atmosphere, but carbon dioxide is a small molecule with a big bite. We have known the mechanism behind this for more than 150 years.

In 1861, John Tyndall discovered that CO₂鈥檚 three atoms vibrate when hit by certain photons. Photons from the sun pass straight through the atmosphere, unhindered by CO₂, but when they reach Earth鈥檚 surface they bounce back as infrared photons 鈥� or heat, in other words.

Instead of passing through the atmosphere, these photons are absorbed by CO₂ and released again, only this time they fly off in random directions. As a result, more heat stays within the atmosphere than goes back out into space. This is the greenhouse effect, a double-edged sword that fosters life, but is also causing rapid global warming.

The other greenhouse gases act in the same way: methane, nitrous oxide, CFCs, ozone and water. Because there is so much of it, water vapour is the biggest heat trapper, but human activity is not directly increasing the atmosphere鈥檚 water content. What we are doing is digging up fossil stores of carbon in the shape of coal, gas and oil. When we burn them to produce energy, we release CO₂. Some CO₂ is taken up by plants and returned to the soil, some is absorbed by the oceans, and some is stored in rocks that react with CO₂ when exposed to air. But these natural processes cannot keep up with the rate at which we are releasing greenhouse gases.

The final blow is CO₂鈥檚听extraordinarily long life. It can stay in the atmosphere for thousands of years, so each molecule we produce adds to atmospheric concentrations and thickens Earth鈥檚 blanket. 鈥淚f we want the temperature to fall,鈥� says Ed Hawkins at the University of Reading, UK, 鈥渨e will have to invent a way to remove CO₂ from the air on a huge scale. In the meantime we鈥檒l need to adapt to a warmer world.鈥� Julia Brown

This article appeared in print under the headline 鈥淟iving with climate change: The new normal鈥�