16 August 2012
It’s already too hot, as Greenland melt record is smashed
|Greenland melt index (2012 red bar) Source: Marco Tedesco|
by David Spratt
News today of a dramatic increase in melting of the Greenland ice sheet this northern summer, and the likelihood of a new record low in summer Arctic sea-ice extent, demand a new look at what safe climate action means.
Today, Marco Tedesco, assistant professor of Earth and atmospheric sciences at The City College of New York, reported that melting over the Greenland ice sheet shattered the seasonal record in the modern era, a full four weeks before the close of the melting season. The melting season in Greenland usually lasts from June – when the first puddles of meltwater appear – to early September, when temperatures cool. This year, cumulative melting by 8 August had already exceeded the record of 2010 (chart above, year 2012 in red). “With more yet to come in August, this year’s overall melting will fall way above the old records. That’s a goliath year — the greatest melt since satellite recording began in 1979,” said Professor Tedesco.
|Greenland melt in 2012 (Marco Tedesco)|
It is the latest in a rush of dramatic news from the Arctic in recent weeks, where this year’s summer sea-ice melt may well break the record low set in 2007, amid growing expectations of the Arctic becoming sea-ice free in summer within the decade, and perhaps sooner.
The Arctic, where global warming is greatest and some of the most dramatic impacts are being witnessed, is the canary in climate warming coal mine.
And the canary is dying. Arctic summer sea ice cover is in a “death spiral” according to Mark Serreze, director of the US National Snow and Ice Data Centre (NSIDC).
Only one conclusion can be drawn as the Arctic ecosystem is being rapidly transformed into a landscape that would not have been recognisable a decade or two ago. At just 0.8ºC of global warming, it is already too hot, and climate change has already gone too far if you value a safe climate in which biodiversity and all the world’s marvellous ecosystems are maintained.
As proposed in A sober assessment of our situation, even the current level of warming for an extended period of time is very risky, yet warming will exceed and be maintained well above 1ºC for the greenhouse gases already in the atmosphere. It is now obvious that as well as reducing greenhouse emissions to zero, drawing down atmospheric carbon on a large-scale is necessary. And so too is short-term geo-engineering such as incoming radiation management — if it can be done with relative safety — to stop too much warming whilst the other two strategies have time to work. We are now living in a world of making the least-worst choices.
2012 IN THE ARCTIC
Headlines this northern summer tell the story:
- Record heat in May rewrote weather records in Greenland, setting the stage for a big summer melt.
- Arctic Ocean floating sea-ice set a record for the largest June sea ice loss in the satellite era. Arctic lost a record total of about 2.86 million square kilometres of ice. At the end of the month, Arctic sea ice extent was 1.18 million square kilometres below the 1979-to-2000 average.
- In July, NASA released findings showing surface melt had been observed on more than 97 per cent of the Greenland ice sheet over a few days, a rate unprecedented in the era of satellite observation, and pictured in dramatic satellite images. Most previous similar events were clustered around a period 7000 years ago when variations in the sun’s axis tilt sent more sunshine to extreme northern latitudes, warming them up. There is no such solar tilt now, but the melt is occurring just the same, according to Mark Serreze.
- In late July, Climate Central reported that that the reflectivity of the Greenland ice sheet, particularly at the high elevations that were involved in the mid-July melt event, had declined to record lows. This indicated that the ice sheet was absorbing more incoming solar energy than normal, potentially leading to 2012 being another record melt year in a long-standing trend of increasingly higher melt seasons.
- On 15 August, Marco Tedesco’s findings of record melting on Greenland were released.
- In early August, a huge, long-lived Arctic ocean storm decimated the sea ice area which was melting out at a record rate, before the high waves and winds shattered the Siberian side of the ice cap. Sea-ice extent is currently tracking below the previous record low of 2007.
- New research finds sea ice loss is 50 per cent higher than previously thought. On 10 August, The Guardian reported that data from the first purpose-built satellite launched to study the thickness of the Earth’s polar caps – the European Space Agency’s CryoSat-2 probe – indicate that 900 cubic kilometres of summer sea ice has disappeared from the Arctic Ocean over the past year, and “in a few years the Arctic ocean could be free of ice in summer, triggering a rush to exploit its fish stocks, oil, minerals and sea routes.”
- The combination of melting sea ice and changing reflectivity of the Arctic surface, and global atmospheric warming, are contributing to the high rate of warming in the Arctic, where temperatures are increasing up to four times faster than the global average.
- The radical decline in sea ice around the Arctic is at least 70% due to human-induced climate change, according to a new study, and may even be up to 95% down to humans – rather higher than scientists had previously thought.
Melting in the Arctic is accelerating, and the region has proved to be more sensitive to global warming than previously thought.
“Very soon we may experience the iconic moment when, one day in the summer, we look at satellite images and see no sea ice coverage in the Arctic, just open water,” says Dr Seymour Laxon, of the Centre for Polar Observation and Modelling at University College London.
Runaway loss of Arctic sea ice may now be inevitable and more worrying, and very likely, is the collapse of the giant Greenland ice sheet, according to climate tipping point expert Dr Tim Lenton. He told the Planet Under Pressure conference earlier this year “The (Arctic sea ice) system has passed a tipping point” that could soon make ice-free summers a regular feature across most of the Arctic Ocean, based on a day-by-day assessment of Arctic ice-cover data collected since satellite observation began in 1979.
And Australia-based scientists say the Arctic region is fast approaching a series of imminent “tipping points” which could trigger a domino effect of large-scale climate change across the entire planet with “major consequences for the future of human kind as climate change progresses.”
A GRAPHIC STORY
Sea ice extent: The following graph shows the extent of summer sea ice in 2012 (blue line) compared to the 1979-200 average (grey line) and the record low of 2007 (dashed green line). The area of ice at the summer minimum in the last five years has been 4.3–4.6 million square kilometres, just over half of what it was 30 years ago.
|Arctic sea ice extent to 13 August 2012. Source: NSIDC|
Sea-ice thickness: There is less ice, and it is now much thinner and more fragile. And the proportion of thick, older ice that lasts from one year to the next is shrinking even faster. Researchers now find that new, first-year ice is less reflective than old ice, for most of the year, anyway. It absorbs more heat from the sun, which means it doesn’t just melt faster: it actually speeds up its own melting.
Sea-ice volume: The new Cryo-Sat2 data suggests that the volume (area X thickness) has reduced around 70% over the past 30 years. According to CryoSat, in 2004 there was about 13,000 cubic kilometres of summer sea ice in the Arctic. In 2012, there is 7,000 cubic kilometres, almost half the figure eight years ago. If the current annual loss of around 900 cubic kilometres continues, summer ice coverage could disappear in about a decade in the Arctic. CryoSat “has shown that the Arctic sea cap is not only shrinking in area but is also thinning dramatically.”
This research is very similar to Arctic sea ice volume graph (graph below) as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center. The red line is 2012.
|PIOMAS daily ice volume|
Prediction the year zero: Depending on what assumption you make about the nature of sea-ice volume decline, “best fit” lines to the PIOMAS data show an ice-free Arctic as early as 2015 (red line) but in most cases within a decade (graph below). It feels as though more and more in the cryosphere research community now see a summer sea-ice-free Arctic as likely within a decade.
|Sea-ice volume trends|
Whilst scientists urge caution about the implications of the CryoSat-2 data, the conclusions are nevertheless dramatic. Dr Seymour Laxon, who analysed the data, told the BBC: “We have to be cautious until our data has been properly analysed as part of a climate model, but this does suggest that the Arctic might be ice-free in summer for a day at least by the end of the decade.”
Regional warming: Global average temperatures have warmed just less than 1ºC since the Industrial Revolution, but average temperatures in Siberia, Alaska and western Canada are now 3ºC to 4ºC warmer than 50 years ago. Recent research finds that “The Arctic is warming two to four times faster than the global average”, with big implications for the fate of the Greenland ice sheet and sea-level rises.
Storms: A new NASA study shows that the rising frequency and intensity of Arctic storms over the last half century, attributed to progressively warmer waters, directly provoked acceleration of the rate of Arctic sea ice drift, long considered by scientists as a bellwether of climate change.
Northern hemisphere weather: Arctic changes are affecting weather patterns across the northern hemisphere. Professor Chris Rapley says “that with the temperature gradient between the Arctic and equator dropping, as is happening now, it is also possible that the jet stream in the upper atmosphere could become more unstable. That could mean increasing volatility in weather in lower latitudes. And there is evidence linking Arctic amplification to extreme weather in mid-latitudes. Scientists are now just beginning to understand how these profound Arctic shifts may be increasing the likelihood of more persistent and extreme weather.”
Biodiversity: Changes in the Arctic have profound implications for its ecosystem, discussed here.
Albedo feedback: The loss of sea-ice is a positive feedback. As white reflective ice is replaced by dark seas, more energy is absorbed. A new study in July 2012 noted: “Loss of sea ice contributes to ground level warming… When it (ice) is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it.”
|Mass change of Greenland ice sheet
2002-2012 from GRACE satellite (to March 2012)
Greenland: Those circumstances as well as rising global temperatures will increase the rate of melting of the Greenland ice sheet, which is already accelerating. Total ice sheet mass loss in 2011 was 70 per cent larger than the 2003-2009 average annual loss rate of 250 gigatons per year. And now, today, we have news of a record melt in 2012 with another month of the melt season to go.
And now the tipping point for Greenland’s ice sheet (eventual sea level rise of 7 metres) has been revised down from around 3ºC to just 1.6ºC (uncertainty range of 0.8-3.2ºC). At the current temperature rise of 0.8ºC we may have already reached Greenland’s tipping point, and with temperature rises in the pipeline (global emissions still rising, no reasonable agreement to reduce them), we are very likely to hit 1.6ºC in two, or three, decades.
The albedo (reflective capacity of a surface, measured as a percentage) of the Greenland ice sheet, particularly the high-elevation areas where snow typically accumulates year-round, have reached a record low since satellite records began in 2000. This indicates that the ice sheet is absorbing more energy than normal. Albedo has dropped significantly in 2012 (black line). There are more charts here.
|Greenland ice sheet albedo 2500-3200 m.
Source: Box and Decker
/Byrd Polar Research Center
Professor Andreas Muenchow of the University of Delaware says “The Greenland ice sheet is changing rapidly before our eyes.” While ‘‘no individual glacier will be the canary in the coalmine’’, he says recent warming had transformed the overall ice sheet. ‘‘The Greenland ice sheet is being reduced not just in size, but in volume,’’ he said. ‘‘The big and broader climate change story is what’s happening all around Greenland.’’
Tipping point: Recent data suggests it would not be an unreasonable bet that Greenland has already passed significant tipping points, but that is something that we will really only know in retrospect. If all the sea-ice is lost in summer, with big implications for albedo changes and greater regional warming, is it possible for the Greenland ice sheet to remain substantially intact in the long run? Given what we know about melting on Greenland now, it seems the answer could only be “no”. If that’s the case, then the inevitable loss of summer sea-ice likely in the next decade also means that Greenland will also pass a significant tipping point unless we act with great urgency.
Permafrost: And there is the fate of the region’s permafrost. I’ve discussed this before here and here. Predictions in 2011 suggested that as soon as 2020 carbon emissions from melting permafrost could be close to a billion tonnes a year. Researchers said that this positive permafrost carbon feedback will “will change the Arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88 per cent of the total global land sink”.
Work by Celia Bitz, Philippe Ciais and others suggests that the tipping point for the large-scale loss of permafrost carbon is around 8–10ºC regional temperature increase. As temperatures rise, it is projected that Arctic amplification (the multiple by with the Arctic warms compared to the global average) would be approximately times three, so around a 3C increase in global temperature is probably more than enough to detonate the permafrost timebomb.
This feedback in the carbon cycle would drive temperatures significantly higher. Caias told the March 2009 Copenhagen science conference that: “A global average increase in air temperatures of 2ºC and a few unusually hot years could see permafrost soil temperatures reach the 8ºC threshold for releasing billions of tonnes of carbon dioxide and methane”. And yet these days there are prophets a plenty who say that keeping below 2ºC is all but politically impossible.
What starts with Arctic sea-ice loss does stop with the sea-ice. It’s but the first domino in a chain that is lined up and primed to fire. But with political action at emergency speed and a safe climate strategy, it does not need to happen like this.