The Earth’s climatic system is enormously complex. However, basic physics has long told us that the composition of the atmosphere has a profound influence on our climate, and that, if the composition of the atmosphere changes, so too will the climate. The UK Government Office for Science provides a clear account of the science of climate change. Below, we draw out the key points.
The climate is naturally variable
The Earth’s climate is driven by the sun’s energy. The amount of energy remaining in the earth system, and the amount reflected back into space, depends on the reflectivity of the earth’s surface and the composition of the atmosphere (of gases, clouds and particles). The composition of the atmosphere creates a natural ‘greenhouse effect’ whereby energy is trapped in the system and heats it up. Indeed, without this the world would be too cold to inhabit.Changes in its composition will affect the planet’s energy balance and thus its climate.
People are affecting the climate
An enormous amount of research is being devoted both to detecting changes in our climate, and to attributing these observed changes to plausible causes. The evidence is reviewed periodically by the Intergovernmental Panel on Climate Change (IPCC). Their most recent assessment reflects the scientific consensus on climate change and its impacts. The Earth’s climate naturally varies over long time-scales, but over the past 20 years it has become increasingly evident that human activity is causing excessive warming.
The warming is attributed to human activity releasing additional greenhouse gases (GHG) into the atmosphere, creating an enhanced greenhouse effect. Several GHGs are involved, although carbon dioxide (CO2) is the most important according to the IPCC. Atmospheric CO2 concentrations are now far higher than at any time in the past 600,000 years and emissions of this and other GHGs, directly or indirectly as a result of human actions, continue at an accelerating rate.
Our effect on the climate could have dangerous consequences
Climatic changes as a result of the greenhouse effect created by these emissions are already being felt and will become ever more disruptive into the future.
Global warming will increasingly impact on an environment already rendered fragile by human activity, putting people, species and whole ecosystems at risk.
The precise effects of the changes on specific regions or localities remain difficult to predict with confidence, but the overall impacts will be profound. Climatic zones will shift, rainfall patterns will change, sea-levels will rise and the intensity of storms will increase. Up to 40% of all species could be threatened with extinction under plausible scenarios.
Data suggest that the Earth’s average surface temperature has already warmed by some 0.75 degrees centigrade since 1900.