by Judith Curry
Some interesting news on the Arctic front.
Arctic climate and sea ice was discussed previously on these two threads:
2011 sea ice season update
The NSIDC has the latest observations and information on the progression of the summer sea ice melt in the Arctic. From their latest summary (dated Aug 3):
Arctic sea ice extent averaged for July 2011 reached the lowest level for the month in the 1979 to 2011 satellite record, even though the pace of ice loss slowed substantially during the last two weeks of July. Shipping routes in the Arctic have less ice than usual for this time of year, and new data indicate that more of the Arctic’s store of its oldest ice disappeared.
Average ice extent for July 2011 was 7.92 million square kilometers (3.06 million square miles). This is 210,000 square kilometers (81,000 square miles) below the previous record low for the month, set in July 2007, and 2.18 million square kilometers (842,000 square miles) below the average for 1979 to 2000.
On July 31, 2011 Arctic sea ice extent was 6.79 million square kilometers (2.62 million square miles). This was slightly higher than the previous record low for the same day of the year, set in 2007. Sea ice coverage remained below normal everywhere except the East Greenland Sea.
The latest sea ice extent image shows that since about Jul 20 that the sea ice extent is slightly greater than that for the same period in 2007, reflecting a slow down in the rate of sea ice extent loss.
The SEARCH Sea Ice Outlook is an international effort to provide a community-wide summary of the expected September arctic sea ice minimum. Monthly reports released throughout the summer synthesize community estimates of the current state and expected minimum of sea ice—at both a pan-arctic and regional scale. The intent of the SEARCH Sea Ice Outlook effort is not to issue predictions, but rather to summarize all available data and observations to provide the scientific community, stakeholders, and the public the best available information on the evolution of arctic sea ice.
The latest outlook was released on Jul 13, using end of June sea ice info:
We received 16 responses for the Pan-Arctic report (Figure 1), with estimates in the range of 4.0 to 5.5 million square kilometers for the September arctic mean sea ice extent. The median value was 4.6 million square kilometers; the quartile values were 4.3 and 4.7 million square kilometers, a rather narrow range given the intrinsic uncertainty of the estimates on the order of 0.5 million square kilometers. It is important to note for context that all 2011 estimates are well below the 1979–2007 September climatological mean of 6.7 million square kilometers.
There continues to be a consensus for continuation of an anomalously low sea ice extent similar to the values for 2008-2010 and below all previous values before 2007. The data show a continuing low value of sea ice extent at the beginning of the summer season and an appearance of a weather pattern (the Arctic Dipole) that tends to favor summer sea ice loss, in contrast to weak and variable summer winds of previous decades. Ocean changes may also be involved. According to the National Snow and Ice Data Center (NSIDC), arctic sea ice extent for June 2011 was the second lowest in the satellite data record since 1979. These new factors over the last several years seem to be holding the September sea ice extent at persistent low values below 5.0 million square kilometers.
I assume that we will see another round of forecasts (based on Jul data) within a week or so.
So why does the minimum sea ice extent matter? Well the state of the sea ice matters to people who live in the region, resource extraction activities, and general transportation issues (see the Arctic Imperative section below). In the context of the climate change debate, the Arctic is regarded as a bellwether for global climate change, and there is general interest in climate related records and their possible attribution to AGW.
While these data are most often interpreted in the context of a linear trend, it is instructive to interpret the record in the context of a (qualitative) change point analysis, defined by changes in trend, mean value, amplitude of the annual cycle, and interannual variability.
- 1979-1988: little trend, consistent interannual variability in the amplitude of the annual cycle.
- 1989-1996: small negative trend (more prominent in the summertime minima), large interannual variability.
- 1997- 2003: lower values relative to the period prior to 1996, with the most noticeable decrease in ice extent being the wintertime maximum; small amplitude and fairly regular annual cycle.
- 2003-2007: marked decrease in wintertime maxima; strong negative trend in both winter max and summer min; continued small amplitude of the annual cycle. A steady decline in wintertime maxima from 2003 to 2007 seems to have led the decline in summertime minima, with a marked decline beginning in 2005 that culminated in the major anomaly of summer 2007.
- 2007-present: return to a large amplitude annual cycle (with an increase in the wintertime max), but with a an overall shift to lower summertime values. The winter 2011 values look anomalously low, possibly with a pattern resembling 2006.
My previous post discusses the apparent impact of teleconnection regimes such as the AMO, NAO and PDO on the interannual variability and trends.
Of relevance to how the actual September minimum will play out, we need to understand the impact of weather variability on shorter subseasonal timescales to understand how the details of the ice freeze up will play out. A big storm in early Aug could further break up the existing ice: decreasing the ice concentration) but increase the ice extent. An early snowfall on existing ice could help speed up the freezing of melt ponds on the existing ice. Once September arrives, a high pressure system with few clouds could speed up the autumnal freezing. A heavy snowfall in autumn could drastically reduce the winter ice growth. Etc. We shall see how this all plays out.
On thin ice?
Sea ice extent is only part of the sea ice story: ice thickness is a critical indicator of the state of the sea ice. The European Space Agency (June 21) reports on the first ice thickness map of the Arctic from its new CryoSat2 satellite.
The first map of sea-ice thickness from ESA’s CryoSat mission was revealed today at the Paris Air and Space Show. This new information is set to change our understanding of the complex relationship between ice and climate.
From an altitude of just over 700 km and reaching unprecedented latitudes of 88º, CryoSat has spent the last seven months delivering precise measurements to study changes in the thickness of Earth’s ice.
CryoSat measures the height of the sea ice above the water line, known as the freeboard, to calculate the thickness. The measurements used to generate this first map of the Arctic were from January and February 2011, as the ice approaches its annual maximum.
The data are exceptionally detailed and considerably better than the mission’s specification. They even show lineations in the central Arctic that reflect the ice’s response to wind stress.
“It has taken about ten years to convert the initial proposal into a flying mission: ten years of hard work and dedication from a core team of less than a hundred people, ably assisted with crucial expertise from a few hundred more.”
ESA’s CryoSat Mission Manager, Tommaso Parrinello, added, “These first results are very exciting as we begin to see the mission’s potential realised.
“The coming months will be dedicated to completing the picture to gain better insight into how polar ice is changing.”
This is exciting news. Determination of sea ice thickness from satellite is not straightforward, so research on on the methodology is ongoing. Some previous efforts at satellite-derived sea ice thickness were made using NASA’s IceSat.
Sea ice variations in the late Holocene
From Copenhagen, news of a new paper to be published in Science on sea ice variations over the last 10,000 years. Quotes from the lead author Svend Funder:
“Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years. During the so-called Holocene Climate Optimum, from approximately 8000 to 5000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50% of the summer 2007 coverage, which is absolutely lowest on record. Our studies also show that when the ice disappears in one area, it may accumulate in another. We have discovered this by comparing our results with observations from northern Canada. While the amount of sea ice decreased in northern Greenland, it increased in Canada. This is probably due to changes in the prevailing wind systems. This factor has not been sufficiently taken into account when forecasting the imminent disappearance of sea ice in the Arctic Ocean.”
“Our key to the mystery of the extent of sea ice during earlier epochs lies in the driftwood we found along the coast. One might think that it had floated across sea, but such a journey takes several years, and driftwood would not be able to stay afloat for that long. The driftwood is from the outset embedded in sea ice, and reaches the north Greenland coast along with it. The amount of driftwood therefore indicates how much multiyear sea ice there was in the ocean back then. And this is precisely the type of ice that is in danger of disappearing today,” Funder says.
“Our studies show that there are great natural variations in the amount of Arctic sea ice. The bad news is that there is a clear connection between temperature and the amount of sea ice. And there is no doubt that continued global warming will lead to a reduction in the amount of summer sea ice in the Arctic Ocean. The good news is that even with a reduction to less than 50% of the current amount of sea ice the ice will not reach a point of no return: a level where the ice no longer can regenerate itself even if the climate was to return to cooler temperatures. Finally, our studies show that the changes to a large degree are caused by the effect that temperature has on the prevailing wind systems. This has not been sufficiently taken into account when forecasting the imminent disappearance of the ice, as often portrayed in the media,” Funder says.
This is a very interesting and important paper. I have long been frustrated by the lack of a good paleo record of sea ice extent over the past several thousand years. The reason is that the signature of sea ice is not obvious or unambiguous in the various paleo proxy records. The driftwood on the coast of Greenland is an interesting proxy for sea ice extent.
Some alarming news from Joe Romm: “NSIDC bombshell: Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020’s, releasing 100 billion tons of carbon by 2100.” The post refers to the following paper:
Amount and timing of permafrost carbon release in response to climate warming
K. Schaefer, T. Zhang, L Bruhwiler, A. Barrett
Abstract. The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO2 concentrations and amplify surface warming to initiate a positive permafrost carbon feedback (PCF) on climate. We use surface weather from three global climate models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29–59% decrease in permafrost area and a 53–97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.
Well, permafrost and its feedback with climate change is a known unknown, and after this paper, I would say it is still a known unknown. I’m not dismissing the paper at all (I haven’t read it), plus permafrost thawing is one of the genuine possible tipping points associated with AGW. But given the assumptions in the paper apparent from the abstract, I don’t see anything here to justify Romm’s alarm.
Moderation note: This is a technical thread that will be moderated for relevance. A companion thread “Arctic Imperative” (forthcoming tonite) will provide a forum for discussion of socioeconomic, policy, and political issues in the Arctic.