The Arctic has clearly undergone significant changes in average temperatures and sea ice extent during the last couple of decades but what does the future hold?
Overland et al. (2013) investigated Arctic climate over the next 30 years using recent climate model projections (CMIP5) for mitigation and business-as-usual scenarios. The results suggested that a seasonally nearly ice-free Arctic Ocean is highly likely before 2050. A mitigation emission scenario could lead to a 7°C temperature increase in late Autumn by the end of the century compared to a 13°C rise for business-as-usual. There is a large gap between modelled results and extrapolated sea ice loss from observations. However, what is clear, is that 'it is very likely that the Arctic climate will continue to show major changes over the next decades' with expanded areas of open water for longer periods, permafrost degradation and dramatic ecological consequences.
Difficulties in projections
Projecting future sea ice loss from global climate models comes with major difficulties and uncertainties, and this difference depends on the proposed timescale in question. Firstly, different models hindcast and forecast different results due to variations in formulas (sea ice physics, clouds, radiation, atmospheric and ocean dynamics) and parameterisation. Internal variability also means that results can differ from modelled near-term projections despite similar initial conditions. For the CMIP5 model used, 80% of the 56 ensemble 1979-2011 member trends are smaller than observed.
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| 1966 to 2005 annual mean SAT based on observations (left) and the 36 CMIP5 models ensemble mean (right) (Overland et al., 2013) |
In contrast, longer-term projections are heavily dependent on the future emission pathway used:
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| Monthly Arctic temperature anomalies for emission scenarios RCP4.5 (blue) and RCP8.5 (red) (Overland et al., 2013) |
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| Sept 1900 to 2100 Arctic sea ice extent based on model simulations and compared against historical and observed records (Overland et al., 2013) |
Hi Carole, interesting post on climate change impacts on the sea ice and its projections! Among different sources of uncertainties in sea ice loss projections, which one do you think will be the most significant to affect the result of projection?
ReplyDeleteHi,
DeleteThanks for the comment!
The significance of uncertainties in influencing the projection of future sea ice is dependent on the time-scale in question. So, more near-term projections over the next few decades are heavily impacted by the model parameters chosen and internal variability of the Earth system - and this is evident from the deviation of modelled sea ice extent from what we have observed in the last few decades.
On the other hand, longer-term projections are highly dependent on the future emissions trajectory - whether we follow a business-as-usual or mitigation scenario will have a large impact on the amount of or lack of sea ice remaining in the Arctic at the end of this century.