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. More...

2.1 What changes have already been observed?

2.1.1 Recent records of increasing temperatures; melting glaciers, 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 increase of greenhouse gases in the atmosphere induced by human activities. More...

2.1.2 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. More...

2.2 How is the Arctic climate expected to change in the future?

2.2.1 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 greenhouse gas emissions,
• 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 20^th 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). More...

2.2.2 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). More...

	Over land areas	Over oceans
Increase in average temperatures	3-5°C (5.4-9°F)	up to 7°C (12.6°F)
Increase in winter temperatures	4-7°C (7.2-12.6°F)	7-10°C (12.6-18°F)

2.2.3 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%. More...

2.2.4 Sea ice 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. More...

2.2.5 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 marine systems. More...

2.3 At what speed are those changes expected to happen?

2.3.1 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 possible.

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. More...

2.3.2 There are many thresholds 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 climate (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 to. More...

2.3.3 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. More...