Polar bears on the sea ice of the Arctic ocean, near the North Pole.
While changes in Earth ecosystems from predicted warming have been reported in nearly all biomes (biological communities), recent climate change seems to be impacting the Arctic region the most.
As Arctic temperatures rise, precipitation rates, and snow/ice cover volumes, begin to change as well. In some cases, this has lead to an increase in vegetation (shrubs and grasses), which can have the beneficial effect of reducing atmospheric CO2, but which can also cause a disruption in the trace gas exchange (such as with methane, CH4) between earth and atmosphere. Also, many of these climate change impacts produce imbalances within ecosystems (the web of interactions between species, and between species and their environments) and these can and do jeopardize long-term species survival; some species (such as reindeer) gain advantage (at least in the short term) from these alterations, while others (like the ringed seal) are threatened by them.
In a recent review of the scientific literature on Arctic climate impacts (Post et al, Ecological Dynamics Across the Arctic Associated with Recent Climate Change, Science Magazine, 11 Sept. 2009), the authors presented the findings of the most up to date impact studies. What follows is a run-down of some of the main findings of this review:
- Lengthening of the growing season in aquatic and terrestrial systems caused by earlier onset of spring melts. Plant flowering and invertebrate appearance (e.g., insects) have advanced up to 20 days in the past decade in several areas.
- Early spring rains have lead to the “washout” of sub-nivean (sub snow level) lairs of ringed seals (Pusa hispida) resulting in increased vulnerability to predation and hypothermia of seal pups.
- Decreased mortality and increased fecundity and abundance of Svalbard reindeer (Rangifer tarandus platyrhynchus).
- Changes in sea ice dynamics and “external nutrient loading” are affecting most heavily those animals with limited distribution and specialized feeding behaviors; examples: the ivory gull (Pagophila eburnean), Pacific walrus (Odobenus rosmarus divergens), ringed seal, hooded seal (Cystophora cristata), narwhal (Monodon monoceras), and polar bear (Ursus maritimus). Note: the polar bear has been experiencing rapid declines in birth rates due to loss of sea-ice habitat.
- Enhanced lake stratification due to warming, and increased nutrient loading from more rainfall, has changed the migration patterns of several fish species, increasing the probability of colonization of fishless lakes and altering these lakes’ ecosystem structure and function (with unknown consequences; possibly beneficial to certain fish species).
- Range expansion of Low Arctic trees and shrubs is having broad ecological consequences, including altering “trace gas exchange”, further impacting land-atmosphere GHG balances.
- Animal invasions due to range shifts (made possible by warming) will continue to alter simple Arctic systems. For example, two species of geomitrid moth are rapidly expanding in the birch forests of northern Scandinavia and Finland, leading to an alteration in the atmospheric carbon budgets of many Arctic regions.
- Populations of arctic fox (Alopex lagopus) are declining in some Arctic regions in parallel with the northward range expansion of red foxes (Vulpes vulpes), believed to be also the result of warming
- Earlier growing seasons have lead to “trophic mismatches” (nutrient or feeding availability mismatches) wherein seasonal, animal births (e.g., the calving of caribou, R. tarandus) do not occur earlier as well, leading to a mismatch in the peak demand for resources and the availability of those resources. This may be contributing to reduced reproduction and survival rates of the caribou.
- Warming induced, temporal changes in plant-herbivore relationships is altering food webs. Herbivores control a good deal of plant productivity and so determine nutrient availability. Food web alterations can lead to imbalances of a single or nutrient hoarding species, impacting the survival of all other species in that habitat (this is especially true for aquatic systems). For example, the recent climate-driven collapse of small rodent population cycles threatens to alter nutrient interactions and ecosystem processes.
- Increasing summer temperatures may increase insect populations and potential reduce the annual caribou harvest that many local and traditional (human) communities depend on.
The review’s author s also noted experimental studies that indicate possible feedback consequences from vegetation responses to warming. Recent controlled warming experiments showed an increase by two weeks in the time period that tundra acts as a carbon sink, which is generally a good thing. However, experimental evidence has shown that the expansion of shrubs and vegetation is altering biogeochemical cycles across the Arctic, leading to feedbacks with the atmosphere, and which complicate predictions of future climate change impacts in the region.
The review concludes with identifying areas of research “in need of immediate emphasis”. These include:
Conservation (preserving habitat),
Dynamics outside the growing season ( the ecological, geological, and climatic interrelationships that are often over-looked, as they are more indirect or complex),
Trophic Interactions (how various nutrient sources [organic molecules, plants, microbes} interact with each other, with abiotic sources [snow, ice, rock, water], and determine their bio-availability in response to climate changes, as noted earlier),
“Heterogeneity” (the highly variable responses of ecosystems to climate forcings) as a “buffer against climate change in the Arctic”,
Scale dependence of climate responses (disagreements among study results may be a consequence of a “disparity of scales”, since actual climate experiments are necessarily conducted at much smaller scales of time and space (can results be “scaled up” or are they limited in predictive ability by their scale?),
“Extreme events” (e.g., insect outbreaks, sudden but transient temperature changes, wild fires, sudden releases of melt water from glaciers, etc.) , tipping points (the point at which equilibrium or ecological balance can not be maintained or restored, and irreversible effects set in) and resilience (the ability of some species–plant and animal–to rapidly adapt to climate change and to the effects of said change, such as diseases,
(Lastly) Baseline studies (in order to increase scientists’ ability to make quantified assessments of how ecological changes may occur in other systems that are currently less affected) to aid future ecosystem management efforts.
top photo: Chief Yeoman Alphonso Braggs, US-Navy
middle image: Richard Lydekker, Mostly Mammals