Climate Change
A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.
On Earth, human activities are changing the natural greenhouse effect. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases [1].
Human influence on the climate system is therefore clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen. Climate change is therefore a natural phenomenon that is being amplified by human activities which currently are making it happen in a much faster way.