16.3.4. Uncertainties and Risks
The polar regions will play a substantial role in driving global climate change
through positive feedbacks to global warming. They also provide us with unparalleled
records of that change. The most important uncertainties, risks, and thus targets
for research are as follows:
- Ocean thermohaline circulation: Will downwelling in the North Atlantic
and the Southern Ocean cease, causing a shutdown of the circulation of the
global ocean? Or will this downwelling simply reduce and eventually recover
with stabilization of GHGs? What is the role of changing input of freshwater
from Arctic rivers?
- Antarctic ice sheet: What will be the contribution of the Antarctic
ice sheets to global sea-level rise over the coming centuries? Although it
is likely that the Antarctic ice sheet will provide some degree of mitigation
of predicted sea-level rise, there is a small risk that the West Antarctic
ice sheet (or portions of it) may retreat rapidly, causing a greater than
predicted rise.
- Marine biology: What will be the response to predicted climate change
of the structure of marine communities and the overall productivity of polar
oceans? Uncertainty arises because existing biological models are not yet
sufficiently developed to provide authoritative and quantitative estimates.
There is some risk of unforeseen collapse of parts of the marine biological
system, with consequent global effects—particularly on fisheries.
- Arctic ice sheets, glaciers, and ice caps: What is the current and
future magnitude of freshwater input to the oceans from ice masses? What is
the impact on global sea level and the thermohaline circulation on decadal
to century time scales, and how can uncertainties in estimates be reduced?
- Permafrost: As ice-rich permafrost degrades, what will be the magnitude,
spatial extent, and variability of its impacts? Will increases in the thickness
of the active layer in currently cold, continuous permafrost be sufficient
to cause widespread damage to human infrastructure? How important is soil
organic carbon sequestered in the upper layer of permafrost in the context
of the world carbon balance?
- Arctic hydrology: Will the balance between increased precipitation
and evapotranspiration lead to a drier or wetter Arctic landscape? What will
be the water balances of the large river basins that generate freshwater inflow
to the Arctic Ocean?
- Arctic sea ice: Is it possible that with increased open water in
the Arctic Ocean, summer sea ice in the Arctic eventually could disappear
completely? The risk is that substantially more open water could generate
large changes in regional climate for countries on the Arctic rim.
- Fluxes of greenhouse gases: What are the current and future fluxes
of GHGs from polar oceans and landscapes? In particular, what is the likely
future role of gas hydrates?
- Stresses on human communities in the Arctic: Can Arctic communities
survive the combined stresses of globalization and marked changes in their
local environments that may result from climate change? Traditional lifestyles
will be threatened, but the communities that practice these lifestyles may
be sufficiently resilient to cope with these changes, as they have in the
recent and distant past.
