limate changes

Rising levels of greenhouse gases are expected to cause changes in climate. Already, the global average surface temperature has increased by about 0.6oC. Globally, the 1990's was the warmest decade and 1998 was the warmed year since 1861, when instrumental records began. Temperature analyses also show that they were also the warmest for the northern hemisphere during the previous 1000 years. As well as temperature changes, snow cover and ice extent has decreased by about 10% since the 1960's, global average sea level has risen and ocean heat content has increased.