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oto.com
Why are Ice and Snow Changing?
A main conclusion of the Intergovernmental Panel on Overall Arctic temperatures have been increasing at
Climate Change (IPCC) Fourth Assessment Report of almost double the global rate. Climate model simula-
2007 was that it is very likely that most of the global tions for the Arctic project further increases in aver-
warming during the last 50 years is due to the increase age temperatures plus a trend to warmer high and low
in human-made greenhouse gases. temperature extremes.
The largest recent increases in annual temperatures In Antarctica the recent warming has not been wide-
for the planet are over the North American Arctic, spread, but model projections for the end of the 21st
north central Siberia and on the Antarctic Peninsula. century indicate a broader pattern of warmer surface
The climate system is influenced both by natural vari- temperatures.
ability and external factors such as greenhouse gases Ongoing changes to ice and snow have a predominant-
and the sun. During the 21st century the most impor- ly positive feedback effect which will result in acceler-
tant external influence on snow and ice will be the in- ating rates of change.
crease in greenhouse gases.
CHAPTER 1 HIGHLIGHTS 9