The sea ice loss rate seems to be very sensitive to model resolution and has improved in CMIP5 — implicating aspects of the model structure as the main source of the problem.
For three particular mismatches —
sea ice loss rates being much too low in CMIP3, tropical MSU - TMT rising too fast in CMIP5, or the ensemble mean global mean temperatures diverging from HadCRUT4 — it is likely that there are multiple sources of these mismatches across all three categories described above.
Not exact matches
They then used the satellite record of Arctic
sea ice extent to calculate the
rates of
sea ice loss and then projected those
rates into the future, to estimate how much more the
sea ice cover may shrink in approximately three polar bear generations, or 35 years.
«Until the
rate and likely duration of
sea ice losses as well as the ensuing ecosystem responses are better understood, closing the U.S. Arctic to commercial fishing is a prudent measure.»
Many researchers think this is unrealistic and that the
rate of
ice loss will accelerate, which means that
sea level could rise much faster than predicted.
The IPCC's latest prediction for
sea level rise — 0.2 to 0.6 metres by 2100 — takes this
ice loss into account but it is based on the assumption that the
rate of
ice loss will remain constant.
Complementary analyses of the surface mass balance of Greenland (Tedesco et al, 2011) also show that 2010 was a record year for melt area extent... Extrapolating these melt
rates forward to 2050, «the cumulative
loss could raise
sea level by 15 cm by 2050 ″ for a total of 32 cm (adding in 8 cm from glacial
ice caps and 9 cm from thermal expansion)- a number very close to the best estimate of Vermeer & Rahmstorf (2009), derived by linking the observed
rate of
sea level rise to the observed warming.
Lead author Dr Malcolm McMillan from the University of Leeds said: «We find that
ice losses continue to be most pronounced along the fast - flowing
ice streams of the Amundsen
Sea sector, with thinning
rates of between 4 and 8 metres per year near to the grounding lines of the Pine Island, Thwaites and Smith Glaciers.»
Since 1979, winter
sea ice extent has decreased 3.2 percent per decade (the
loss is much more pronounced in summer at a
rate of 13.4 percent per decade).
Other researchers look at raised beaches [32] and palaeo lakes to record previous
rates of isostatic uplift and
rates of
sea level rise [33, 34]; this can help constrain previous
ice volumes and
rates of
ice loss.
Joughin et al. (2010) applied a numerical
ice sheet model to predicting the future of PIG, their model suggested ongoing
loss of
ice mass from PIG, with a maximum
rate of global
sea level rise of 2.7 cm per century.
This kind of significant change could increase the
rate of warming already in progress, affect further
sea ice loss in the Arctic and alter shipping access to the Arctic Ocean.
Rates of
sea - level rise calculated from tide gauge data tend to exceed bottom - up estimates derived from summing
loss of
ice mass, thermal expansion and changes in land storage.
Our modelled values are consistent with current
rates of Antarctic
ice loss and
sea - level rise, and imply that accelerated mass
loss from marine - based portions of Antarctic
ice sheets may ensue when an increase in global mean air temperature of only 1.4 - 2.0 deg.
Our experiments show a clear threshold in the relationship between the
rate of
sea - level rise, and the
rate of (
sea - level contributing)
ice - sheet mass
loss.
Non-linear
rates of Antarctic
ice loss under high
rates of
sea - level rise Golledge, Nick; Arnold, Richard; Levy, Richard; Naish, Tim
From recent instrumental observations alone we are therefore unable to predict whether mass
loss from these
ice sheets will vary linearly with changes in the
rate of
sea - level rise, or if a non-linear response is more likely.
Under all RCP scenarios the
rate of
sea level rise will very likely exceed that observed during 1971 — 2010 due to increased ocean warming and increased
loss of mass from glaciers and
ice sheets.
The authors of the study — Ricarda Winkelmann and Anders Levermann from the Potsdam Institute for Climate Impact Research, Ken Caldeira of the Carnegie Institution for Science and Andy Ridgwell of the University of Bristol — find that the
loss of the entire Antarctic
ice sheet would take millenniums, but up to 100 feet of
sea level rise could result within 1,000 years, with the
rate of the rise beginning to increase a century or two from now.
8) Accelerated mass
loss in Greenland and / or Antarctica, perhaps with another huge
ice shelf breaking off, but in any case coupled with another measurable rise in the
rate of
sea level rise, 9) The Fifth Assessment Report (2012 - 2013) really spelling out what we face with no punches pulled.
IIRC, the limit on mass
loss was attributed to the narrowness of passes in the mountains, but if the
ice loss is behind the mountains as the ocean reaches beyond them, and mixes salt into the system with tides, then only the flushing of salt and icebergs via meltwater would limit the
rate of melt in the (brand new) Greenland
Sea.
However, although the Arctic is still not as warm as it was during the Eemian interglacial 125,000 years ago [e.g., Andersen et al., 2004], the present
rate of
sea ice loss will likely push the system out of this natural envelope within a century.
The contribution from glaciers and
ice caps (not including Greenland and Antarctica), on the other hand, is computed from a simple empirical formula linking global mean temperature to mass
loss (equivalent to a
rate of
sea level rise), based on observed data from 1963 to 2003.
The reasonable agreement in recent years between the observed
rate of
sea level rise and the sum of thermal expansion and
loss of land
ice suggests an upper limit for the magnitude of change in land - based water storage, which is relatively poorly known.
Individual responses continue to be based on a range of methods: statistical, numerical models, comparison with previous
rates of
sea ice loss, composites of several approaches, estimates based on various non
sea ice datasets and trends, and subjective information (the heuristic category).
However, despite near normal
rates of
ice loss during the month, June 2015 was a relatively warm month (Figure 7) with 925 hPa air temperatures up to 2.5 C higher than average near the North Pole and East Siberian
Sea, with even warmer air temperatures in the Kara
Sea (up to 4.5 C).
Individual responses continue to be based on a range of methods: statistical, numerical models, comparison with previous
rates of
sea ice loss, estimates based on various non-
sea ice datasets and trends, and subjective information (the «heuristic» category).
As the
rate of
ice loss has accelerated, its contribution to global
sea level rise has increased from a little more than half of the total increase from 1993 - 2008 to 75 - 80 percent of the total increase between 2003 - 2007.
If both Greenland and West Antarctica shed the entirety of their
ice burden, global
sea levels would rise by 12 to 14 m. Although these icecaps would not disintegrate within a century, the
loss of even a third of their mass — quite plausible if the
rate of polar
ice loss continues to double each decade — would force up the oceans by at least 4 m, with disastrous socioeconomic and environmental consequences.
It may be worth considering that if climate models are underplaying the actual amount of Arctic
sea ice loss, and if Arctic
sea ice loss is a positive feedback on global temperature, then, the observed
rate of Arctic
sea ice loss ought to be applying a warming pressure over and above that from greenhouse gas emissions.
I think the best predictor for
sea level rise are measurements of the mass
loss rates and the acceleration of those mass
loss rates for the Greenland and Antarctic
ice caps.
Polyak et al. (2010) looked at Arctic
sea ice changes throughout geologic history and noted that the current
rate of
loss appears to be more rapid than natural variability can account for in the historical record.
A new study published in the journal Science revealed that CO2 emissions are accelerating the
rate of
sea ice loss in the arctic.
The resulting enhanced
loss of summer and winter
sea ice resulted in feedbacks, associated with Arctic Amplification, which has raised Arctic air temperatures at a
rate twice the global average.
«It is very likely that the
rate of global mean
sea level rise during the 21st century will exceed the
rate observed during 1971 — 2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and
loss of mass from glaciers and
ice sheets.
Sea ice minimum levels are falling at the
rate of 14 % a decade in the Arctic, and polar bears have been feeling the
loss.
Considered in isolation, the reduction in ocean heat transport implies a possible moderation in the
rate of Arctic
sea ice loss in the coming decade.
The July 2010
Sea Ice Outlook Report is based on a synthesis of 17 individual pan-Arctic estimates using a wide range of methods: statistical, numerical models, comparison with observations and rates of ice loss, composites of several approach
Ice Outlook Report is based on a synthesis of 17 individual pan-Arctic estimates using a wide range of methods: statistical, numerical models, comparison with observations and
rates of
ice loss, composites of several approach
ice loss, composites of several approaches.
In addition, the study showed that
ice loss rates have not only sped up at the grounding lines, but also more than 100 miles inland, compromising the entire
ice sheet that the glacier helps hold back from the
sea.
Influences from the
rate of melting, of thin
ice, and
loss of multi-year
sea ice in 2012 were underestimated, even by objective methods.
Further, it only took one month of persistent wind conditions to slow the
rate of
sea ice loss, resulting in an increase in 2009
sea ice extent compared to 2007 and 2008.
«The current
rate of
sea ice loss, and the reduced thickness of large areas of the
ice remaining, suggests that we may see yet another record minimum in summer
sea ice extent this year.»
Loss rate for May and June 2013
sea ice extent was slower than May and June 2010 and 2011 and slower than June in 2012 (Figure 3).
Warming is contributing to the
loss of protective
sea ice along Alaska's northwestern coast, leading to increased
rates of coastal erosion.
Individual responses continue to be based on a range of methods: statistical, numerical models, comparison with previous
rates of
sea ice loss, estimates based on various non-
sea ice datasets and trends, and subjective information (i.e., the «heuristic» category).
Direct measurements of the AMOC are only available for the past ten years or so, but Yeager et al. present a combination of observation - and model - based evidence that suggests that the Atlantic thermohaline circulation (THC, which is closely related to AMOC) transitioned from a weak state in the 1970s to a strong state in the 1990s and that this strengthening contributed to the accelerated
rate of winter
sea ice loss that was observed in the late 1990s.
Instead, natural variations in the climate system and other external forcing factors (such as volcanic eruptions) will likely cause the
rate of Arctic
sea ice change to vary considerably from decade to decade, and perhaps even temporarily switch from negative (
sea ice loss) to positive (
sea ice growth).
There is a thermostat in action there, the more heat in the Arctic
seas the faster
rate it is lost to space, until the
ice recovery insulates again and modifies the heat
loss.
Mass gains of the Antarctic
ice sheet exceed
losses Mass changes of the Antarctic
ice sheet impact
sea - level rise as climate changes, but recent
rates have been uncertain.
As discussed here, relative to the years of greater
ice loss in Greenland, the
rate of
sea level rise should have dropped by an additional 1.3 mm / year in 2014.