Climate change: effects on terrestrial ecosystems
Arctic ecosystems are particularly vulnerable to climate change. A circumpolar study has concluded that climate change has a stronger influence on ecosystems in the Arctic than other factors such as changes in land use, other perturbations, and pollution. There are only a few plants and animals on land and in fresh-water systems in Antarctica, but climate change nonetheless has a significant potential impact, particularly on the Antarctic Peninsula. Studies done over the past couple decades have revealed diverse effects of climate change on terrestrial and freshwater species.
According to IPCC, Arctic ecosystems are particularly sensitive to climate change. Studies carried out over the past few decades have demonstrated a range of climate effects on species and ecosystems in fresh water and on land.
Increases in temperature and precipitation will affect ecosystems in a complex way; longer growing season, thawing permafrost, and changes in the water cycle are expected to have the greatest impact on terrestrial ecosystems.
Changes in meltwater runoff from glaciers will change the water temperature in rivers, and influence sediment and nutrient content, which will also have consequences for rivers and lakes downstream. As the loss of ice continues, ”old” pollution stored in snow and glaciers will be released to the environment.
Vegetation and growing season
Altered snow cover – both in terms where the snow is and when it melts away in the spring – will influence vegetation. Experiments involving manipulation of snow cover show that the relationships are complicated. Early melting does not necessarily lead to greater productivity, but if species from more temperate regions become established owing to higher temperatures, the net effect on vegetation may be increased productivity in places where there is less snow or a shorter snow season.
Altered snow cover – both in terms where the snow is and when it melts away in the spring – will influence vegetation. Experiments involving manipulation of snow cover show that the relationships are complicated. Early melting does not necessarily lead to greater productivity, but if species from more temperate regions become established owing to higher temperatures, the net effect on vegetation may be increased productivity in places where there is less snow or a shorter snow season. NDVI increased by 15.5% in the North American Arctic and by 8.2% in the Eurasian Arctic.
Under MOSJ, work has begun to monitor the growing season in Svalbard. Satellite mapping in Svalbard has shown that the growing season on average begins before 1 July in only 15% of the vegetated areas in the archipelago. Adventdalen, near Longyearbyen, is one of the areas where the growing season begins earliest, in places even before 20 June (average for 2000-2010). Examination of satellite data also reveals major year-to-year variations in the start of the growing season. In the central parts of Svalbard in 2002 and 2006, the growing season started between one and two weeks earlier than in 2000 and 2008. This time-series is as yet too short to allow definitive conclusions about trends. However, on-the-ground observations from Svalbard suggest that there is a trend toward a shorter snow season (and thus a longer growing season), as there were fewer days with snow cover in the 1990s and 2000s than in the 1970s and 1980s. See the indicator Snow cover duration on MOSJ
The growing season in the Arctic is very short to start with, so even small changes in its length will, over time, have consequences for most resident plants and animals. The plant communities will experience a direct effect in the form of increased growth and changes in community structure and composition. These changes may provide better living conditions for some species of animals, and counteract some of the negative effects of climate change.
In Greenland, extensive studies have focused on the timing of reproduction and phenological development of important forage for reindeer, and shown that a warming climate leads to earlier development of these plants. However, the timing of calving has not changed very much; thus there is now an unfortunate temporal mismatch between the availability of forage plants of good quality and reindeer calving.
In Svalbard, it has been noted that the geese are arriving a few days earlier in the spring, though it is not yet clear whether this will have a measurable positive impact on reproduction or survival. However, it is worth nothing that the pink-footed goose, which is now seen in larger numbers than previously, grazes on many of the same plants as the Svalbard reindeer, thus having a direct impact on the species composition and structure of the vegetation. This type of situation can lead to greater competition for food resources. Read more about this in the article «Record numbers of geese cause problems on the tundra».
The ultimate effect that changes in the length of the growing season will have on the ecosystem as a whole remains far from certain.
In the Arctic, the ground is frozen year-round everywhere except under glaciers. This is permafrost. Every summer the uppermost layer – the active layer – thaws, allowing vegetation a brief and hectic time to blossom. Permafrost stabilises the ground. Studies show that in some places, the permafrost is 2°C warmer now than 20-30 years ago. A monitoring series reported in MOSJ demonstrates thawing also in Svalbard. This may have impact on both terrestrial and freshwater systems owing to physical changes, which can directly affect growing and living conditions for plants and animals, and hence indirectly affect organisms that rely on these plants and animals for sustenance.
A warmer summer climate increases the likelihood that new parasites and other pests can become established. This can also affect the local biota. In Svalbard, for example, studies have shown that the fertility of Svalbard reindeer is impaired by parasite load.
The short growing season and relatively low temperatures in the Arctic appear to impede establishment and reproduction of most alien plant species, and such invading species currently constitute only a small fraction of the total Arctic biodiversity. However, rising temperatures and increasing human presence imply that more alien species will gain a foothold in the Arctic. In Svalbard, 51 introduced plant species have been registered, of which eleven appear to have established stable populations. At present they are restricted to the settlements, but three species are considered to have potential to spread into the natural vegetation.
In brief about some species in Svalbard
The Arctic fox population is generally declining in Arctic regions, perhaps owing to climate change. In Svalbard, however, there are few signs of any long-term changes in the Arctic fox population. Arctic foxes in Svalbard have no competition from red foxes and are not dependent on lemmings and other small rodents, unlike arctic foxes in other parts of the Arctic. This makes Svalbard’s arctic foxes less sensitive to climate change than their relatives in other arctic regions. Still, in time they will be affected by how climate change impacts their prey: seals, reindeer, seabirds, waders, and Svalbard rock ptarmigan.
At present we cannot predict how climate change will affect the Svalbard rock ptarmigan. Many gaps remain in our knowledge about this species’ ecology, life in winter, migration routes and how the population varies. However, the ptarmigan may be vulnerable to changes in climate because of increased competition for forage when goose populations grow. The ptarmigan may also be subject to a temporal mismatch between when access to forage is optimal and when their eggs hatch. It has been shown that ice on the tundra increases winter mortality and reduces reproductive success because less food is available; slumps in the ptarmigan population are completely synchronised with rainy winters.
For the Svalbard reindeer, longer summers and more vegetation may be an advantage, and the observed increase in the population over the past decade suggests a positive response to a longer growing season, even though the reindeer are negatively affected by increased frequency of ice-bound forage owing to milder temperatures.
The big picture
Both Svalbard and Jan Mayen are isolated islands. Their endemic species have established themselves over millennia and adapted to extreme conditions. The isolated location of the polar regions protects terrestrial mammals against invading species from the south. On the other hand, if the current fauna cannot tolerate changes in climate, no new mammals will migrate in to replace them. At present there are no indications that the endemic mammals of Svalbard are threatened with extinction because of expected climate change, but many studies have shown that such changes affect these species, and may in the long run influence population size and distribution.
Uncertainties remain concerning the effects of more mild and rainy winters, and the potential impact of new parasites.
In the terrestrial and freshwater ecosystems of Antarctica, many climate-related changes have been demonstrated. Ecosystems generally respond to warming and increased availability of meltwater with population growth, increased biomass, and greater complexity in the invertebrate and plant communities.
The two plants – Deschampsia antarctica and Colobanthus quitensis – have become more common in some coastal areas in Antarctica, owing to climate change. Warmer temperatures speed up growth and dispersal of existing plants, and promote establishment of new seedlings.
Changes in temperature and precipitation have increased biological productivity in lakes, mainly because the period with ice cover is shorter. Some lakes have become more saline because of a drier climate.
Some of the negative consequences are related to disappearance of local sources of meltwater, leading to lower humidity and more arid conditions. Other effects of human activities include physical destruction of habitats and introduction of alien species. These constitute a greater threat to parts of the terrestrial environment in Antarctica than does climate change. Nonetheless, it is probable that the combined effects of climate change and other human influences will have significant impact on both environment and ecosystems.
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