The impacts of climate change will be widespread across the globe. Emissions of greenhouse gases have already altered the earth's atmosphere and the climate is already changing. We will live with the consequences of these changes for the next few decades, regardless of the actions we take now to reduce our emissions. However, beyond that time, future climate change depends on whether we continue to emit greenhouse gases into the atmosphere at the rate we currently do, or whether we take effective steps to dramatically reduce our emissions.
The difference between these two courses of action is the difference between some inevitable climate change, and more severe, "high-end" climate change in the longer term. This is a decision that faces politicians at the global climate change negotiations at Copenhagen in December.
In order to understand more about what the human impact of high-end climate change might be, and therefore what would happen if a successful agreement can not be reached at Copenhagen, the United Kingdom's Met Office Hadley Centre has produced a map outlining some of the impacts that may occur if the global average temperature rises by 4 degrees Celsius (7 degrees Fahrenheit) above the pre-industrial climate average.
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The map was produced by the Met Office Hadley Centre, but contains contributions from climate scientists from other institutions conducting the latest research on climate impacts.
Although the average temperature rise over the globe is 4 degrees Celsius (7 degrees Fahrenheit) the projection on the map shows that this average rise will not be spread uniformly across the globe. The land will heat up more quickly than the sea, and high latitudes, particularly the Arctic, will have larger temperature increases. The average land temperature will be 5.5 degrees Celsius above pre-industrial levels.
The impacts on human activity shown on the map are only a selection of those that may occur, and highlight the severe effects on water availability, agricultural productivity, extreme temperatures and drought, the risk of forest fire and sea level rise.
Agricultural yields are expected to decrease for all major cereal crops in all major regions of production. The availability of water will be affected by melting of glaciers, particularly in areas such as the Indus basin and western China, where much of the river flow comes from melt water. Population increases, combined with changes in river run off as a result of changes in rainfall patterns and increased temperatures, could mean that by 2080 significantly less water is available to approximately 1 billion people already living under water stress. For many areas of the world sea level rise, combined with the effect of storms, will threaten low lying coastal communities. There are often very dense populations living along coasts, as well as important infrastructure and high value agricultural land, which makes the impact of coastal flooding particularly severe. The intrusion of salt water on farming land, and the risk to lives of flooding events could affect millions of people worldwide every year.
The impacts are frightening, and the list is not exhaustive. However, the map represents a world where climate change has gone unmitigated, where we have continued to emit greenhouse gases at the rates we are today. If we continue to do this, then the likelihood of the planet warming by 4 degrees Celsius (7 degrees Fahrenheit) increases, and as it does so the risk of these impacts being realised also increases. By taking strong and effective action to curb greenhouse gases emissions, it may be possible to limit this temperature rise to 2 debrees Celsius (4 degrees Fahrenheit). Although this would still bring some adverse impacts, the risk of the very severest impacts, as shown in the Met Office Hadley Centre map, is significantly reduced.