from the Earth’s heat balance. If all ice and snow were Some of the feedbacks and interactions that result from
to disappear, and the effect of this were to be evened out warming in the polar regions are complex and very hard
across the globe, the Earth would receive 3 to 4 watts more to predict. In the Arctic there is another positive climate
heating per square metre than it does now
4
. For compari- feedback that may amplify global warming significant-
son, scientists believe that the climate forcing from all the ly. The uppermost part of the frozen tundra contains
additions and subtraction resulting from greenhouse gas- between 200 and 400 billion tonnes of carbon stored
es, particulate matter, aerosols, solar radiation changes, in organic material produced by the tundra vegetation
2

and volcanic eruptions over the last hundred years equal (Chapter 7). This organic material breaks down slow-
about 1.6 watts per square metre
3
. This illustrates that the ly and if the permafrost starts to thaw, decomposition
ice and snow covered surfaces in high latitude and high will speed up and release the greenhouse gases meth-
altitude regions contribute an important and essential ane and carbon dioxide. In addition, there are probably
cooling function for the whole planet. some thousand billion tonnes of methane frozen deep
Heat
Arctic Ocean
release
to air
Heat
release
to air
Atlantic Pacific
Ocean Ocean
Shallow
warm current
Indian
Ocean
Heat
Southern Ocean
release
to air
Deep current
cold and saline
Figure 2.1: Thermohaline circulation, showing areas of major ocean–air heat transfer.
22 GLOBAL OUTLOOK FOR ICE AND SNOW