GUIDE TO CLIMATE CHANGE

Climate forecast

In 2001, scientists predicted the Earth would warm by 1.4 - 5.8C by 2100.
Most of the warming, they believed, was a result of humanity's use of fossil fuels, like oil and coal.
The scenarios (right) compare a fossil-fuel driven future with one where sustainable development is a priority.

Greenhouse effect

The greenhouse effect is the natural process by which the atmosphere traps some of the Sun's energy, warming the Earth enough to support life.
Most mainstream scientists believe a human-driven increase in "greenhouse gases" is increasing the effect artificially.
These gases include carbon dioxide, emitted by fossil fuel burning and deforestation, and methane, released from rice paddies and landfill sites.

The carbon cycle

Carbon dioxide (CO2) is the main greenhouse gas of concern. A finite amount of carbon is stored in fossil fuels, the sea, living matter and the atmosphere.
Without human influence, transfers between these stores roughly balance each other – for example, plants absorb carbon as they grow, but release it as they decay.
But when humans cut down trees or burn fossil fuels, they release extra carbon into the atmosphere, increasing the

Feedback effects

Warming will trigger some processes which speed further warming, and other effects which mitigate it. The balance between these positive and negative feedbacks is a major cause of uncertainty in climate predictions.
For example, as the diagram shows, decreasing ice cover will mean exposed land absorbs more heat and speeds warming further.
In contrast, for example, plants' CO2 intake is likely to increase as higher temperatures increase growth rates, somewhat countering the warming effect.

Gulf Stream

Dramatic temperature shifts have happened in the past, driven partly by changes in a major ocean currents.
A "great ocean conveyor" helps transport heat around the globe via surface and deep-sea movements of water.
Scientists are exploring whether global warming might slow or shut it down - a scenario considered "low probability, high impact".
This could disrupt mostly wind-driven surface currents such as the Gulf Stream, which helps to bring milder weather to Northern Europe.