Alice Westenra of Ohoka School asks :-

What is the latest knowledge of global warming?

David Wratt, a climate physicist with National Institute of Water and Atmospheric Research Ltd, responded.

The Earth's temperature has always gone up and down. For example 100 million years ago (the time of the dinosaurs) it was warmer than now, and there have also been ice ages when it was several degrees colder. These changes were natural effects. However it appears that human activities are now starting to change the climate. There is more carbon dioxide in the atmosphere now than at any time during at least the last 650,000 years. Scientists know this from measuring bubbles of air trapped in Antarctic ice. Most of this increase has been caused by the burning of fossil fuels like coal and petrol by humans. Carbon dioxide is a `greenhouse gas', and scientists expect that as more of it builds up in the atmosphere the Earth will continue to get warmer.

The temperature of the Earth increased by about 0.6 degrees Centigrade during the 20th Century. Most of the warming from 1950 to 2000 was probably caused by increasing amounts of greenhouse gases. More warming is expected in future. This could amount to between 1.4 degrees and 5.8 degrees Centigrade over the coming 100 years unless there is an effort by many countries to substantially reduce greenhouse gas emissions.

This warming is expected to cause a rise in sea level, and may lead to more heavy rain and floods in some places and also more droughts in some areas. Over a longer period (several hundred years) it is even possible that much of the ice in Greenland and a large amount of Antarctic ice could melt, raising sea levels by several metres. However there are things which humans could do to slow down global warming. For example. We might be able to trap carbon dioxide from power stations that burn coal or oil, and put it back down under the ground. We could use more wind generators for electricity, and use public transport more. We could better insulate our houses so we don't have to burn so much coal and oil to make electricity for heating and cooling. And we could plant more forests, as trees take carbon dioxide out of the air and turn it into wood.