think climate. think change.
Our climate is the result of the interaction of the Sun's radiation with the atmosphere, oceans, polar ice and the land. Many processes contribute to our climate, including the absorption and emission of heat by materials such as gases and water, reflection of heat from different surfaces such as snow and trees and the circulation of the oceans and atmosphere.
Climate models are the best tools we have for projecting future climate. This includes assessing the effect of human activities on climate over the coming decades, and explaining the causes of climate change over past decades.
A climate model is a simplified mathematical representation of the Earth's climate system. Models have a three-dimensional grid of points over the globe, extending into the ocean and the atmosphere. Regional models can provide more detailed information over a smaller area. Since regional models operate at finer resolution than global models, they give a much better representation of the effect of topographic features such as mountain ranges and local variations in climate. Climate models can reproduce present climatic features reasonably well, along with past climatic changes such as the last Ice Age and the global warming of the 20th century.
Economists and other experts have developed a number of scenarios or possibilities for how the world might develop over the next century based on a set of assumptions, such as how fast population might increase and how quickly renewable energy sources might replace fossil fuels. In 2000, a set of greenhouse gas and aerosol emission scenarios for the 21st century were developed for use in climate model simulations. Research groups around the world use these scenarios to project climate changes. The results are featured in the report of the Intergovernmental Panel on Climate Change (www.ipcc.ch/).
A wide range of scenarios for global temperature rise is possible, the lowest are the most likely to be exceeded. However, even the most optimistic scenario for stabilising carbon dioxide concentrations at 450-550ppm in the atmosphere would lead to a warming of 1 to 3°C by the year 2100. This level of warming is considered by some scientists to represent a major threat for some regions and some ecosystems. Other systems may benefit from warming e.g. high latitude agriculture. The challenge facing us now is to determine how much we need to reduce our carbon dioxide emissions to minimise the risk of dangerous climate change.
Schematic representation of a climate model. Various physical quantities such as temperature and rainfall are typically computed in half-hour time steps over a three-dimensional grid.
