mate variables other than temperature – such as precipi- and snow have high albedo. This means that they reflect
tation or wind conditions
11
. most of the solar radiation. With warmer polar tempera-
tures, the area of sea ice and snow cover decreases, expos-
Antarctica ing new expanses of ocean and land surfaces that absorb
an increased amount of solar radiation. This increase of
The temperature trends for Antarctica show that late 20th total absorbed solar radiation contributes to continued
century warming was primarily along the Antarctic Penin- and accelerated warming. Many IPCC climate models
sula without significant warming trends elsewhere on the suggest a major loss in sea ice cover by the mid 21st
continent. The proximate cause for the warming on the century caused by albedo feedback from shrinking snow
Peninsula was the increase in the magnitude of the South- cover and increased open water areas in summer
15
.
ern Annular Mode during the period from 1960 to 2001, a
change that implies stronger winds, reduced sea ice, and A second feedback is negative: the cloud-radiative feed-
warmer temperatures upwind of the Peninsula, which back. Its future impact is important but uncertain. In-
contributed to the local warming. There are indications creased cloud cover, an expected result of global warm-
of warming higher up in the atmosphere over Antarctica ing, increases the reflection of solar radiation away
over the last 30 years, but causes cannot be assessed
12
. from the Earth’s surface, but it also increases the net
long-wave radiation emitted downward from the same
Model experiments for the end of the 21st century do clouds back to the surface
16
. The net effect of increased
show broader patterns of warm surface temperatures cloudiness is expected to be a small decrease in radiation
throughout Antarctica. The delay in the response is received by the Earth’s surface.
thought to be the result of the large thermal inertia of the
Southern Ocean
13
or details of the internal physics of the One of the great challenges of climate change science
Southern Annular Mode
14
, but uncertainties are large. is to understand the net effect of these rather complex
interactions (Figure 3.6). This is not just a question of
understanding the physics of climate systems – many
Feedbacks and interactions of these interactions and feedbacks also involve the liv-
ing world. For example, the increase in shrub growth in
Feedback refers to the modification of a process by tundra regions due to high-latitude warming leads to a
changes resulting from the process itself. Positive feed- decrease in albedo in summer, but an increase in snow
backs accelerate the process, while negative feedbacks retention in winter over large areas of land. Another
slow it down. Part of the uncertainty around future cli- feedback comes from melting permafrost that releases
mates relates to important feedbacks between different methane, a powerful greenhouse gas, into the atmos-
parts of the climate system: air temperatures, ice and phere, which then amplifies the greenhouse effect. The
snow albedo (reflection of the sun’s rays), and clouds. need to understand these interactions has led to an in-
crease in interdisciplinary studies in recent years and is
An important positive feedback is the ice and snow a focus of research being conducted through the Inter-
albedo feedback (see also Chapters 2, 4 and 5). Sea ice national Polar Year 2007–2008.
36 GLOBAL OUTLOOK FOR ICE AND SNOW