Arctic Climate Change
2. How is the climate changing in the Arctic?
- 2.1 What changes have already been observed?
- 2.2 How is the Arctic climate expected to change in the future?
- 2.3 At what speed are those changes expected to happen?
Arctic climate is now warming rapidly and much larger changes are projected.
2.1 What changes have already been observed?
Recent records of increasing temperatures; melting
sea ice and
permafrost; and rising sea
levels provide clear evidence of a warming trend for the Arctic
as a whole. For example, in Alaska and western Canada, winter
temperatures have increased by as much as 3-4°C in the past 50
years (i.e. 5.4-7.2°F). In general, winter temperatures are
rising more rapidly than summer temperatures.
Observations also suggest that precipitation may have
increased by roughly 8% across the Arctic over the past 100
years, and that rain now falls mainly in winter, rather than in
spring or autumn.
Both natural factors, such as variations in solar
radiation, major volcanic
eruptions and interactions between the
atmosphere and oceans, and
factors linked to human activities can influence the climate.
Ice cores and other sources
of information about past climatic conditions reveal that the
current warming trend is unusual, and that it reflects the
greenhouse gases in the
atmosphere induced by human activities.
The sea ice presently
covering the Arctic Ocean and neighboring seas is highly
sensitive to temperature changes of the air and of the ocean.
Over the past 30 years, the average area covered by sea ice has
decreased by about 8%, an area larger than Norway, Sweden and
Denmark combined. The average thickness of Arctic sea ice has
also decreased by about 10 to 15% over this time period. A
reduction of sea ice as a result of the warming climate can in
turn affect the climate through changes in water temperatures,
ocean currents, and ocean evaporation rates.
2.2 How is the Arctic climate expected to change in the future?
In order to foresee future
climate change and its
potential impacts, two major factors that determine the impact
of human activities need to be assessed:
- the overall level of future
- the response of the climate system to these emissions
based on possible changes in clouds, ice cover, and effects
on sea level.
Even the most conservative forecasts expect the Earth to warm
more than twice as much in this century than it did during the
20th century. Furthermore, climate models indicate
that the warming in the Arctic will be substantially greater
than the average warming of the planet (in some places of the
Arctic up to twice as much).
Towards the end of this century, annual average
temperatures are projected to rise across the
entire Arctic, with increases of roughly 3-5°C over the land
areas and up to 7°C over the oceans. Winter temperatures are
projected to rise significantly more (see table below).
Over land areas
||up to 7°C
Global warming is already leading to increased evaporation
and, in turn, to increased precipitation. Over
the Arctic, annual total precipitation is projected to increase
by roughly 20% by 2100, with most of the additional
precipitation in the form of rain. The greatest increases are
expected over coastal regions, especially in the winter and
autumn when they are projected to exceed 30%.
has already declined considerably over the past 50 years. By
2100, the average area covered by sea ice is expected to have
declined further and some models project a complete
disappearance of summer sea ice. These reductions in sea ice
will increase regional and global warming as more solar energy
will be absorbed by the darker sea surface and less will be
reflected by the ice.
The area of Arctic land covered by snow has
declined by about 10% over the past 30 years, and an additional
decrease of 10-20% is projected before the end of this century.
This will reduce the beneficial effects of snow cover on certain
plants and animals. Increased rates of melting and refreezing
could prevent some creatures from accessing food or their
nesting sites. This will also affect flows of
freshwater across the land
to the ocean, and transfers of moisture and heat from the land
to the atmosphere and
2.3 At what speed are those changes expected to happen?
While most analyses of climate impacts focus on scenarios of
steady gradual warming, there is a possibility that the warming
could trigger abrupt changes in climate. The
mechanisms that underlie such potential abrupt changes are not
adequately taken into account by current climate models, which
means that surprises are
Records indicate that very large shifts in Arctic climate
patterns occurred very rapidly in the past. For example,
ice core records indicate
that temperatures over Greenland dropped by as much as 5°C (9°F)
within a few years during the period of warming that followed
the last ice age, before abruptly warming again. This sudden
change in the weather over Greenland was apparently driven by
changes in North Atlantic Ocean
salinity that led to a
sharp reduction in the ocean currents that brought warmth to
Europe and the Arctic.
There are many
in the Arctic environment which, if crossed, could lead to
substantial changes in that region and the world.
For instance, the likely temperature increase of 3ºC during
the 21st century is thought to be sufficient to initiate the
widespread and long-term melting of the
Greenland ice sheet. Over
many centuries, this could eventually result in its complete
disappearance and raise global sea level by 7 metres.
Moreover, observed changes in deep water currents in the
Atlantic Ocean, as a result of changes in
sea ice, a…re warning
signals that another threshold may soon be crossed. These
changes in currents could potentially disrupt the
Gulf Stream that brings
warm ocean water to north–west Europe. Its potential
interruption would have massive consequences for the European
(see section on thermohaline circulation).
While much uncertainty remains about which of these
thresholds will be crossed
and when exactly this might occur, records of the past suggest
that the potential for abrupt changes is real. Compared to
changes that occur gradually, abrupt changes will be harder both
(for scientists) to predict and (for societies) to adapt
The speed at which a change takes place may
be more important than the amount of change. For example, if
thawing of permafrost or
increasing coastal erosion were to occur very slowly, people
might be able to replace buildings and roads as part of the
normal replacement cycle of infrastructure. If changes occur
rapidly, adaptation costs
will be significantly higher.