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Arctic warming and its consequences have worldwide implications
The Arctic influences global climate through three major feedback mechanisms, all of which could be affected by global warming. These mechanisms involve the reflection of sunlight, ocean currents, and greenhouse gas releases. More...
As snow and ice are bright white, most of the solar energy that reaches them is reflected back to space. This is one reason why the Arctic remains so cold. As air temperatures are increasing, snow and ice now tend to form later in the autumn and melt earlier in the spring. The darker land and water surfaces, which absorb more of the sun's energy, are thus longer uncovered. This warms the surface further, which, in turn, causes faster melting, creating a ‘positive feedback loop’ that amplifies and accelerates the warming trend (see also Question 4.2). This is one reason why climate change is particularly rapid in the Arctic.
With Arctic warming, forests are projected to expand northward into areas that are currently tundra. Forests are darker than tundra and mask snow cover on the ground, reducing the reflection of sunlight and further increasing warming. However, the resulting warming could be partly offset by larger expanses of forests absorbing more CO2. More...
One of the ways the sun's energy is transported from the equator toward the poles is through the globally interconnected movement of ocean waters primarily driven by differences in heat and salt content, known as the thermohaline circulation (“thermo” for heat and “haline” for salt).
At present, the Gulf Stream current that flows from the Gulf of Mexico to the coasts of Europe warms the winds and provides much of the moisture that falls as precipitation over northwestern Europe. As the water moves northward, it becomes cooler, saltier and denser. As a result, surface water eventually becomes heavier than the water(s) below it and sinks deep into the ocean. This process drives the global seawater “thermohaline circulation” (sometimes referred to as the “conveyor belt”) which pulls warm waters northward. Part of this global circulation is known as the Gulf Stream, providing some of the heat that keeps Europe warmer in winter than regions of North America at the same latitude. Climate change could interfere with the formation of the cold, dense water that drives oceanic circulation and thus bring about further changes in climate.
Slowing the thermohaline circulation would have several major global effects:
Greenhouse gases are exchanged between the atmosphere and Arctic soils and sediments. These processes can also be affected by global climate change and in turn affect it. More...
3.3.1 Carbon is currently trapped as organic matter in the permafrost (frozen soil) of the Arctic. During the summer, when the top layer of permafrost thaws, and plant material on dry land or ponds decomposes, methane – a very potent greenhouse gas – and CO2 are released. Higher temperatures lead to an increase in the rate of decomposition and gas production, and possibly to a feedback loop with more warming that results in more releases, causing more warming, and so on (see also Question 3.1). The replacement of Arctic vegetation by denser and faster growing vegetation from the south could in part offset this effect through a greater uptake of carbon. More...
3.3.2 In the Arctic, vast amounts of methane are trapped in permafrost and in cold ocean sediments in a solid icy form (as methane hydrates or clathrates). A rise in temperature within the soil could initiate the release of methane from permafrost to the atmosphere. This release is a less certain outcome of climate change than the other emissions discussed here because it would probably require greater warming and take more time to occur. If such releases were to take place, the climate impacts could be very large. More...
3.3.3 Currently, the direct effect of the Arctic Ocean on the level of CO2 in the atmosphere is limited. This is due to the presence of sea ice that limits the absorption of CO2 by the water and its uptake by organisms living near the water surface. A reduced ice cover could significantly increase the amount of carbon taken up by the Arctic Ocean. While these changes are likely to be important regionally, the total area affected is not large enough to significantly reduce global CO2 concentrations in the atmosphere. More...
3.4.1 There are 3 100 000 km3 of ice on Arctic lands around the world, containing enough water to raise the global sea level by 8m. Most Arctic glaciers and ice caps have been in decline since the early 1960s, with this trend speeding up in the 1990s. In some areas, the increase in precipitation has outpaced the melting so that a small number of glaciers, especially in Scandinavia, have gained mass during some recent years.
The Greenland Ice Sheet is the largest area of ice on Arctic lands. Part of the top layer of ice of this ice sheet is melting during summer and the area where this is happening increased by about 16% between 1979 and 2002, (which represents) an area roughly the size of Sweden.
Projections from global climate models suggest that the contribution of Arctic glaciers to global sea-level rise will accelerate over the next 100 years. By 2100, the melt of these glaciers will have contributed to a rise of roughly four to six centimeters or even more according to recent estimates. In the longer term, the Arctic contribution to global sea-level rise is projected to be much greater. Some climate models project that local warming over the Greenland Ice Sheet will eventually lead to its complete disappearance, with a resulting sea-level rise of about seven meters. More...
3.4.2 Climate change causes sea level to rise in two ways:
Global average sea level rose almost 3mm (0.12 inches) per year during the 1990s. This is about one millimeter (0.04 inches) more per year than during the decades before that. Global average sea level is projected to rise 10 to 90cm (4 to 36 inches) between 2000 and 2100, with the rise speeding up with time. Over the longer term, much larger increases in sea level are projected.
Sea-level rise is projected to have serious implications for coastal communities and industries, islands, river deltas and harbors. A number of the world’s most populous cities such at Calcutta and Bangkok will be severely affected. More...
3.5.1 Arctic wildlife resources such as seals, reindeer, birds and fish have long been sold on world markets. Arctic seas contain some of the world's oldest and most productive commercial fishing grounds, which provide significant catches for many Arctic countries, as well as for the rest of the world.
Moreover, the Arctic has significant oil and gas reserves, and the mineral reserves in parts of Russia and Canada provide large quantities of raw materials to the world economy. Marine access to resources is likely to be enhanced in many places in a warmer Arctic with less sea ice, but access by land is likely to be hampered due to a shortening of the season during which the ground is sufficiently frozen to drive on. More...
3.5.2 Climate-related changes in Arctic ecosystems will have consequences not only at local level but also on a global scale because of the many links between the Arctic and the rest of the planet. Many species from around the world migrate to the Arctic in summer and depend on it for breeding and feeding. Climate change will alter some of their habitats significantly.
Expansion of the forests towards the North, for instance, may reduce the size of tundra areas, which are important breeding grounds for hundreds of millions of migratory birds. Indeed, a number of bird species are projected to lose more than 50% of their breeding area during this century, including several globally endangered seabird species. More...
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