Beware: the heat is on

PUBLISHED : Saturday, 09 September, 2006, 12:00am
UPDATED : Saturday, 09 September, 2006, 12:00am

Our planet is getting a little hotter every year; it may be just half a degree Celsius in the past 100 years, but some predict the Earth will heat up by as much as seven degrees by 2100.

The effects of rising temperatures are particularly visible at the Poles. Ice cover is shrinking and if the trend continues, increasing temperatures will melt the ice packs and water levels will rise all over the planet.

If all the ice melts, the seas may rise by 70 metres. This won't bother you if you're living on Mount Tai Mo, the highest peak in Hong Kong at 957 metres, but people on reclaimed and lowlands might want to build up those dikes.

Rising seas aren't the only problem: as the polar ice packs melt, climate is also affected. While ice reflects the sun's energy, liquid water absorbs it. Also, when oceans warm and ice thins, a feedback loop is created.

The more open water there is, the slower formation of fresh ice in winter, and the earlier the sprint melt starts the following year.

Scientists worry this chain reaction will change the temperature of oceans, affecting ocean circulation and altering marine ecosystems. As oceans cover about 70 per cent of the Earth's surface, there will be a knock-on effect on the rest of the planet.

The big question is whether this meltdown is a man-made catastrophe due to increased pollution or part of a natural cycle of temperature change.

An ongoing cycle?

Many people think global warming is the result of burning fossil fuels to obtain energy.

They say that if we stopped burning coal, oil and natural gas that release carbon dioxide and a host of other gasses that trap heat in the atmosphere, global warming would decrease.

Others argue that our planet has always suffered periods of intense cold and heat along with rising and falling sea levels. Although we may think that the frozen continents at the top and tail of the planet are a permanent feature, the truth is this is the first time in our planet's 4.6 billion-year- history that we have ever had ice at both poles.

Recent discoveries show the Earth's climate has alternated between frosty ice house conditions and steaming hot house conditions for the past two billion years. While the dinosaurs lived in hot house times, we are living in an ice house era.

The ice epoch we live in has already lasted 30 million years and includes various ice ages along with warmer periods known as interglacials. Typical ice ages last around 100,000 years while interglacials last just 10,000.

As temperatures wax and wane, sea levels and ice cover change. During the last ice age, one third of the planet was covered in glaciers and sea levels were 122 metres lower than today.

As the last ice age ended 10,000 years ago, we are now at the end of an interglacial age. But don't worry, climatologists say change is very gradual and we

probably won't see the full effect of an ice age for 1,000 years.

Matter of degrees

In the 1920s, Serbian geophysicist Milutin Milankovitch suggested climate change was caused by tiny variations in the Earth's orbit around the sun. Earth's course is constantly shifting. Over 100,000 years its orbit swings from an almost perfect circle to an ellipse and then back again. Over every 40,000 years the Earth's tilt varies between 65.6 degrees and 68.2 degrees. Finally, force from the moon and occasional proximity to the sun causes a slight vibration in the Earth's rotation every 22,000 years.

While all these events are quite minor, Milankovitch suggested that together they affect where solar energy arrives: there may be periods when most hits the equator, and at others it will concentrate on one hemisphere. Because the hemispheres are quite different in the amount of land and water they have, they have different heat-storage capacities. This means that when our relationship to the sun changes, the temperature and climate of the planet changes too.

What's next?

There are lots of different ideas put forward about the types of climate changes we can expect to see in the future, and plenty more opinions on what is causing these changes.

Inescapable facts are that the Arctic ice cap been shrinking by 10 per cent a year for the past 25 years, and that more than

13,000 square kilometres of sea ice in the Antarctic Peninsula has been lost in the past 50 years.

Looking globally, sea levels are already rising by about two millimetres a year. What do you think will happen next?