Data from satellites show a drop of 30 per cent in the area of Arctic sea-ice at the end of each summer.From the National Snow and Ice Datacentre (NSIDC) the September average is well below 30%, more like 40%.
NSIDC, September average extent.
Technically in sea-ice science parlance extent and area mean very different things. Extent is the area covered by grid boxes with more than 15% sea-ice, whereas area is the sum of the percentage cover in each grid box. In terms of area, Cryosphere Today provides a time series of satellite observations of area. That shows that the summer minimum has dropped from around 5.5 million to under 3.5 million kmSq, again a drop of around 40%.
The ice is almost half as thick as it was in the 1980s, a fact that only came to light when ice logs kept by the US and British submarines looking for places to surface during the Cold War were finally made public.As I've previously discussed, research into sea-ice thickness has been done based on submarine tracks. During the Cold War the interest in the Arctic sea-ice thickness was motivated by the possibility of using submarines in the Arctic to threaten the USSR with nuclear warheads - submarines under the sea-ice would be undetectable and have quicker 'delivery' times to the USSR. Doubtless the Soviets had a reciprocal interest in the region. The US and British ice thickness data was released to certain scientists to aid research. Indeed for some time Professor Peter Wadhams has had an open invitation to British submarines on missions under the sea-ice. More recent research by the Alfred Wegner institute has recently found substantial additional thinning, e.g. here and here.
The way things are going there will be open water at the North Pole in summer within the next few decades.Models used for IPCC Assesment Report 4 tended to show a seasonally sea-ice free Arctic in the third and fourth quarters of this century. However it has been noted that the current trend of Arctic sea-ice loss is ahead of such model projections, e.g. Stroeve et al. In 2009 a paper by Wang and Overland examined this issue, they took a subset of models from the Coupled Model Intercomparison Project. This subset was derived based upon the model's ability to reproduce the seasonal cycle of sea-ice, the reasoning for this is that the seasonal cycle is forced by a factor external to the Arctic (the changes of sunlight with seasons) in a similar way to which human driven warming is a factor external to the Arctic. They found that using this subset it was possible that the Arctic could see a summer ending with a sea-ice free period within the next 30 years, possibly as early as the late 2020s.
Polar animals are already reacting to the changes. We saw evidence for ourselves when we accompanied a Norwegian team from the University of Svalbard who were making their annual check on the health of polar bears. The bears' condition has been steadily deteriorating as the ice, which they need when hunting seals, diminishes. And cubs born to underweight mothers are much less likely to survive their first years.As I've already mentioned on the previous post the Polar Bear Specialist Group have combined research to give a picture of the status of Polar Bear populations in the Artic. By 2010, of 19 regions, 7 have too little data to say anything, 1 is increasing, 3 are stable, 8 are in decline (source). The statement itself refers to observations of researchers, it's veracity will become apparent when episode 7 is screened.
The loss of sea-ice in the north affects not just polar bears but the whole planet. The frozen Arctic Ocean acts as a huge reflector, bouncing back 85 per cent of the sun's heat back into space. This keeps the polar regions cool and moderates the whole of the earth's climate. But when the ice vanishes the dark sea water that replaces it absorbs the sun's energy so it's temperature rises. This is why the Arctic - a region the size of North America is warming twice as fast as the rest of the planet. As a consequence, increasing amounts of meltwater are now flowing into the polar sea. This could eventually disrupt the flow of ocean currents around the planet that transfer heat around the Earth and are critical in maintaining the climates we've known for centuries. The implications of that are hard to overstate.This is in line with the consensus view of current science. For example, Catlin Arctic Survey, RAPID. It should be noted that where a shutdown is shown, the models don't show it until late in the 21st century. For me a more troubling issue is the potential for more direct changes in atmospheric circulation due to warming in the Arctic and direct impacts of the loss of Arctic sea-ice - increased lower level atmospheric warming in the summer, and increased heat flux to the atmosphere from open ocean or thinner ice during the freeze season.
Meltwater, created by the warming air and accumulating on the surface, cascades down moulins - giant shafts that pierce the ice sheet. There it melts the underside of the glacier so hastening speed of the glacier's descent to the sea. The melt of Greenland's glaciers alone could cause a rise in sea levels of up to half a metre by the end of this century.This is a very clear risk. The regional warming has the potential to make ice wet, this increases the amount of solar energy it absorbs, e.g. Skeptical Science. At present the northern part of Greenland is surrounded by sea-ice, which keeps temperatures down. so whilst in eastern Greenland there have been "Rapid and synchronous" changes (Luckman et al), in the north the melt hasn't yet begun in an organised fashion. If expectations of a rapid transition of the Arctic to a seasonally sea-ice free state are realised, the melt of the north of Greenland will commence. The pattern revealed by recent research is clear, e.g. here, here, here, & here, that Greenland's glaciers are now melting rapidly.
Attenborough also addresses the loss of ice from ice-shelves and recession of glaciers in the Antarctic, with implications for significant increases in sea-level. He closes noting that
What will happen and by how much are difficult questions. But with over half of the human population living near the coast, the answers may be only too devastating.We cannot be certain about sea-level rise, both it's rapidity and scale. However it is possible to bound the uncertainty; IPCC AR4 claimed a 20 to 50cm sea level rise in the 21st century, but this left out sea level rise from Greenland and Antarctica. Pfeffer et al asserted that sea level rise of over 2 metres was unfeasible. So figures within the range 20cm to 2 metres seem reasonable. However what happens over this century is only the start.
Current fossil fuel emissions are causing the atmospheric content of CO2 to increase, this increased level of CO2 will last for hundreds of years, with a residual amount that lasts for around 100,000 years (Archer, 2006). We are committed to more warming than observed because of the slow warming of the oceans and other effects of polution, as I've discussed recently. These two facts combined act together to potentially overcome the slow (in human lifetime terms) response of ice sheets to forcings.
Whilst there is much concentration on sea-level rise this century, to me a more important issue is the huge sea-level rise that paleo-climatic studies suggest will follow. We were in an interglacial called the Holocene (since about 10,000 years ago), arguably now we are in a different period, called the Anthropocene; the era of massive human impact on the planet. Overpeck et al find that during the last interglacial sea levels were of the order of 4 to 6 metres above current levels, and the Greenland and West Antarctic ice-sheets likely had a major role in this sea-level rise. They use a model and find that the Greenland temperatures that lead to that sea level rise were probably less than 3.5 degrees C warmer than today. That may seem like a lot in the context of 0.8 degrees C global warming since 1880 (GISS), but in the context of recent regional warming in the Arctic it is not substantial (GISS). As previously noted, as the Arctic continues it's transition to a seasonally sea-ice free state the warming of Greenland can only proceed and intensify.
The BBC states that it's mission is: "To enrich people's lives with programmes and services that inform, educate and entertain." Source. The series Frozen Planet has fulfilled this mission in full. If part 7 of Frozen Planet: "On Thin Ice" is alarming that is because the situation is alarming, not because Attenborough is being alarmist. In his response to David Attenborough, had Nigel Lawson wished to be objective, instead of being deliberately evasive and obfuscatory, he would have been forced to the same conclusion as David Attenborough, because that is the true state of the science.
Archer, 2006, "Millennial Atmospheric Lifetime of Anthropogenic CO2."
Luckman et al, 2006, "Rapid and synchronous ice-dynamic changes in East Greenland."
Overpeck et al, 2006, "Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise."
Pfeffer et al, 2008, "Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise."
Stroeve et al, 2007, "Arctic sea ice decline: Faster than forecast."
Wang & Overland, 2009, "A sea ice free summer Arctic within 30 years?"