"Models 'key to climate forecasts'"

From the BBC
The only way to predict the day-to-day weather and changes to the climate over longer timescales is to use computer models.

These models solve complex mathematical equations that are based on well established physical laws that define the behaviour of the weather and climate...

Now, current state-of-the-art climate models include fully interactive clouds, oceans, land surfaces and aerosols, etc. Some models are starting to include detailed chemistry and the carbon cycle.

It is worth thinking a little about why these processes are important, and a few examples are highlighted here:

1. Clouds affect the heating and cooling of the atmosphere
For example, on a cloudy day, less radiation (heating) from the sun reaches the Earth's surface and we feel cool.

On the other hand, on a cloudy night the heat generated during the day is trapped and the temperature near the surface remains relatively warm.

However, it is not just the amount of cloud that is important, but also the detailed properties of the cloud. Thin cirrus cloud high up in the atmosphere has a different effect on climate to thick cloud nearer the Earth's surface.

High level clouds let sunlight through and trap infra-red radiation. Their dominant effect is to warm surface climate

Low level clouds reflect sunlight and trap little infra-red radiation. Their dominant effect is to cool surface climate

2. The oceans take much longer to warm up than the land
They also move heat around the globe; for example, the Gulf Stream in the north Atlantic Ocean brings warm water from the tropical Atlantic up to northern Europe, and has a strong effect on the temperatures that the UK experiences.

3. The land surface influences how much radiation is absorbed at the surface
An area that is covered in trees will be dark and will heat up more by absorbing more radiation. Areas covered in ice, or at the opposite extreme desert, will both reflect more radiation and absorb less heat.

4. Aerosols
These are atmospheric particles, such as sulphate and black carbon that are produced naturally from volcanoes and forest fires, as well as by humans from fossil fuel power stations and other industrial activities.

They generally have a cooling effect on climate, by reducing the amount of sunlight reaching the surface (the so-called global dimming effect) and by changing the properties of clouds. The presence of man-made aerosols is reducing global warming in the short term.

5. The chemistry and carbon cycle determine how much carbon dioxide remains in the atmosphere
Currently the biosphere (plants, soils, phytoplankton) absorbs half of the carbon dioxide that man produces.

The latest climate model predictions suggest that this will not continue indefinitely and that some parts of the biosphere (in particular soils) could start to release carbon if temperatures increase too much.