Last week, news outlets reported that April 2016 was the hottest April on record globally. This was the seventh month in a row to have broken global temperature records, and the third month in a row that the monthly record has been broken by the largest margin ever. Meanwhile, recent atmospheric recordings indicate global concentrations of carbon dioxide are poised to remain above 400ppm for the first time in human history (pre-industrial concentrations are estimated to have been around 280ppm).
In recent decades, the Arctic and parts of Antarctica have shown stronger than average global warming (Fig. 1). As a number of scientists are raising the spectre of a ‘climate emergency’, the APPG for Polar Regions invited a panel of experts to tell us about the changes being observed in the polar regions, and whether we should be worried.
The polar cryosphere comprises all the glaciers, ice sheets, sea ice and permafrost, as well as ice on frozen lakes and rivers, found in the Arctic and Antarctic. As these regions become warmer, the cryosphere is likely to be transformed in significant ways. However, so far, the changes observed in the Arctic and Antarctica are quite different.
In the Arctic, scientists are observing rapid warming across most of the region. Sea ice extent in the Arctic has been decreasing rapidly, especially in the summer (~10% per decade). Most glaciers throughout the Arctic are also diminishing.
In Antarctica, a much more complex picture is being observed (Fig. 2). Here, the changes are patchier and more localised than in the Arctic. Some areas are warming, some are staying the same, and some are cooling. In contrast to the Arctic, the extent of sea ice in the Antarctic appears to be increasing, although this is thought to be a result of increasing wind strength, over recent decades, spreading the ice further out into the Southern Ocean during wintertime (Fig. 3). While there is relatively good knowledge of sea ice extent in the Antarctic, rather little is known about how thick it is.
Elsewhere in Antarctica, scientists have been witnessing the loss of permanent ice shelves (i.e. the part of the glacier that floats where it meets the sea) and the thinning of the West Antarctic Ice Sheet, especially on the Antarctic Peninsula.
The loss of ice in the Arctic and Antarctic is likely to have a number of consequences. The seasonal loss of the Arctic sea ice could contribute around 0.5C° to global average temperature due to the disappearance of such a large reflective surface. Antarctic sea ice is also projected eventually to decrease, though since the changes are focused in the winter months when there is little sunlight, the reflective effect would be less strong.
Increased run-off from the melting of glaciers and ice sheets (in Greenland and Antarctica) is making a significant contribution to global sea level rise (see Fig. 4). L sea level projections are complicated by the fact that the loss of glaciers and ice sheets will also affect the Earth’s gravity and land uplift (as the sheer weight of the ice is redistributed), meaning that the experience of global sea level rise is likely to be experienced differently according to regional variations.
To put the threat of global sea level rise into perspective, the risk of a flood event that might overtop the Thames Barrier is a circa 1 in 1000 year risk at current sea levels. This might become a 1 in 10 year event under a sea level rise of 1 metre (a high-end but not implausible scenario by 2100) unless sea defences are improved.
Regardless of what happens with sea levels and atmospheric changes, the melting of the Arctic sea-ice also leaves us confronted with the emergence of a new seasonal ocean (a so-called ‘state change’ in the environment).
One important aspect of Arctic change is the increase in transport of heat through the warm ocean currents that link the Atlantic to the Arctic via the UK, Faroes Islands and Northern Norway. Without sea ice cover in the Arctic, there is the potential for greater wind mixing of the ocean and release of heat. Further, the loss of ice from the Arctic will impact the productivity of these waters, though the projection of this still remains uncertain, despite significant progress in development of predictive models. The wider consequences in terms of the stocks and migrations of different species are poorly understood as there remains a real lack of knowledge about Arctic marine ecosystems and how these, and surrounding waters, might be affected by climate change.
For many of those living beyond the Arctic, the inclination is perhaps to think of the region as a maritime space, dominated by the Arctic Ocean. However, climate change is also affecting life on land in the polar regions, especially in the Arctic. Depending on how one defines the southern boundary, the Arctic covers a land area of between 7 and 21 million km2, and is populated by about 13.1 million people.
As the Arctic has warmed, profound changes have been observed in snowfall and summer warmth. Overall, circa 37% of the Arctic has experienced an increase in vegetation growth over the past thirty years in response to warming (Fig. 5). This is creating conditions for various plant and animal species to spread northwards, although uncertainty remains over which species are likely to migrate in the future (and what pests and pathogens might be included).
Yet warming is also leading to the destruction of existing Arctic ecosystems. In the high latitudes, where winter temperatures used to be far more stable, species such as the polar bear, Arctic fox, snowy owl and reindeer have become specialists at surviving in harsh cold climates. These Arctic species are less able to adapt to temperature changes and snow cover, meaning scientists expect to see a continued decline in their numbers.
An anticipated increase in extreme weather events is also of concern. In 2007, a thunderstorm triggered a wildfire in Alaska which resulted in the release of carbon equivalent to 50 years of storage. Such storms appear to be becoming more frequent. An increasing number of warm spells during the Arctic winter is also being observed. This leads to greater ice formation as snow thaws and later refreezes. The layers of ice that result become a barrier to herbivores such as reindeer which need to be able to dig through to the vegetation below for food. In 2013/14, more than 65,000 reindeer died in Russia during an ice event.
Condensing such a wide array of issues into a single conclusion is not easy. Yet there were perhaps two recurring themes brought out by our expert panel. The first was that both poles exhibit ‘regionality’ in terms of the effects of climate change, although this is much more visible in Antarctica, with some parts (e.g. the Antarctica Peninsula) witnessing far greater rates of change than others. Partly related to this point, the second theme was that the effects of continuing environmental change in the polar regions are not uni-directional. The Earth continues to be a complex system. However, although some opportunities are emerging, overall the changes being observed are likely to have increasingly negative consequences for today’s human societies and ecosystems in both the polar regions and the rest of the world.
Nevertheless, uncertainty remains and when each of our panellists was asked what they would do with £10 million, they identified the following priority areas for future research: to study the effects of ice melt in Antarctica on global sea level rise; to establish long-time series measuring changes in sea-ice thickness; to investigate whether the Arctic Ocean is likely to become more or less productive with reductions in seasonal sea-ice; and to investigate whether the Arctic tundra is likely to become wetter or drier.
This briefing paper was prepared by Dr Duncan Depledge for the All-Party Parliamentary Group for Polar Regions.
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This is not an official publication of the House of Commons or the House of Lords.
It has not been approved by either House or its committees, nor does it represent the views
of the All-Party Parliamentary Group for Polar Regions.