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Climate Change
Many scientists agree that climate change is the biggest threat facing coral reefs around the world. The Earth is getting warmer, and as temperatures rise faster and faster, natural environments such as coral reefs find it hard to adapt to the pace of change. Higher sea temparatures stress the tiny animals that make up corals, leading to coral bleaching and death. Causes of global climate changeGlobal climate change is the result of many complex environmental factors, but a principal cause is the increasing amount of greenhouse gases in the atmosphere as a result of human activity. The most significant greenhouse gas is carbon dioxide, which has increased in concentration by more than a third in the last 200 years due to burning of fossil fuels and deforestation. The concentrations of other gases, such as methane and nitrous oxide, and the ozone-depleting halocarbon gases have also greatly increased over the same period. Greenhouse gases in the atmosphere warm the air by trapping heat from the Sun that would otherwise radiate from Earth back towards space. The warming that results is similar to that which occurs inside a greenhouse. Mathematical modelling of climate change is a complex task because some of the carbon dioxide produced by human activity is removed from the atmosphere by natural processes that can be highly variable. In addition, other gases such as aerosols, and the reduction in ozone cause a decrease in atmospheric temperature. The longevity of different gases in the atmosphere varies. Carbon dioxide is particularly long-lived and likely to persist at elevated levels for centuries. Over the twentieth century, the average temperature of the Earth's surface rose by 0.6°C. According to a recent international study, it is projected to increase by another 1.4 - 5.8°C over the next 100 years. At the same time, average sea surface temperatures have also increased, although at a slower rate. Even small changes in sea surface temperature can have dramatic effects on the global climate. These include changes in ocean circulation patterns; increased frequency of storm events; and rising sea level due to expansion of warmed oceanic water and loss of land ice.
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