ScienceDaily: Close Relationship Between Past Warming And Sea-level Rise
A team from the National Oceanography Centre, Southampton (NOCS), along with colleagues from Tübingen (Germany) and Bristol presents a novel continuous reconstruction of sea level fluctuations over the last 520 thousand years. Comparison of this record with data on global climate and carbon dioxide (CO2) levels from Antarctic ice cores suggests that even stabilisation at today’s CO2 levels may commit us to sea-level rise over the next couple of millennia, to a level much higher than long-term projections from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). …
Nature GeoScience: Antarctic temperature and global sea level closely coupled over the past five glacial cycles doi:10.1038/ngeo557
Ice cores from Antarctica record temperature and atmospheric carbon dioxide variations over the past six glacial cycles. … Our record reveals a strong correlation on multi-millennial timescales between global sea level and Antarctic temperature, which is related to global temperature.
Increased growth in Antarctic sea ice during the past 30 years is a result of changing weather patterns caused by the ozone hole according to new research published this week (Thurs 23 April 2009).
Reporting in the journal Geophysical Research Letters scientists from British Antarctic Survey (BAS) and NASA say that while there has been a dramatic loss of Arctic sea ice, Antarctic sea ice has increased by a small amount as a result of the ozone hole delaying the impact of greenhouse gas increases on the climate of the continent.
GRL: Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent
Geophys. Res. Lett., 36, L08502, doi:10.1029/2009GL037524
Based on a new analysis of passive microwave satellite data, we demonstrate that the annual mean extent of Antarctic sea ice has increased at a statistically significant rate of 0.97% dec−1 since the late 1970s. The largest increase has been in autumn when there has been a dipole of significant positive and negative trends in the Ross and Amundsen-Bellingshausen Seas respectively. The autumn increase in the Ross Sea sector is primarily a result of stronger cyclonic atmospheric flow over the Amundsen Sea. Model experiments suggest that the trend towards stronger cyclonic circulation is mainly a result of stratospheric ozone depletion, which has strengthened autumn wind speeds around the continent, deepening the Amundsen Sea Low through flow separation around the high coastal orography. However, statistics derived from a climate model control run suggest that the observed sea ice increase might still be within the range of natural climate variability.
Recent projections of sea-level rise after a future collapse of the West Antarctic Ice Sheet for example, the Fourth Intergovernmental Panel on Climate Change Assessment Report) assume that meltwater will spread uniformly (that is, eustatically) across the oceans once marine-based sectors of the West Antarctic are filled. A largely neglected 1977 study predicted that peak values would be 20% higher than the eustatic in the North Pacific and 5 to 10% higher along the U.S. coastline. We show, with use of a state-of-the-art theory, that the sea-level rise in excess of the eustatic value will be two to three times higher than previously predicted for U.S. coastal sites.
Supporting online material
Article from “ScienceDaily“
University of Toronto and Oregon State University geophysicists have shown that should the West Antarctic Ice Sheet collapse and melt in a warming world – as many scientists are concerned it will – it is the coastlines of North America and of nations in the southern Indian Ocean that will face the greatest threats from rising sea levels.
Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.
Supporting online material
From the Science Podcast [mp3]: an interview with Jonathan Bamber on a reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet.
The Wilkins Ice Shelf is at risk of partly breaking away from the Antarctic Peninsula as the ice bridge that connects it to Charcot and Latady Islands looks set to collapse. The beginning of what appears to be the demise of the ice bridge began this week when new rifts forming along its centre axis resulted in a large block of ice breaking away.
Autosub, a robot submarine built and developed by the UK’s National Oceanography Centre, Southampton, has successfully completed a high-risk campaign of six missions travelling under an Antarctic glacier.
Autosub has been exploring Pine Island Glacier, a floating extension of the West Antarctic ice sheet, using sonar scanners to map the seabed and the underside of the ice as it juts into the sea. Scientists hope to learn why the glacier has been thinning and accelerating over recent decades. Pine Island Glacier is in the Amundsen Sea, part of the South Pacific bordering West Antarctica. Changes in its flow have been observed since the early 1970s, and together with neighbouring glaciers it is currently contributing about 0.25 mm a year to global sea level rise.
 At the current rate of 3.3 mm/yr, this one glacier is contributing 7.6% of current sea level rise.
Nature: Lower carbon dioxide triggered Antarctic ice sheet formation , doi:10.1038/nature08447
From the Natural Environment Research Council:
East Antarctica started to ice over around 34 million years ago when atmospheric levels of the greenhouse gas carbon dioxide (CO2) dropped to twice the levels they are at today, report researchers in Nature. ‘This is the largest and most important climate tipping point of the last 65 million years.‘ – Professor Paul Pearson, Cardiff University
Pearson’s team showed that CO2 levels dropped to around 760 parts per million just before the ice sheet started to take hold. But levels of the gas bounced back soon after, before beginning a steady decline towards today’s levels. ‘Our work shows that there does appear to be a relationship between ice sheet formation and atmospheric CO2 levels, which is what the climate models suggest‘ adds Pearson.
Pearson et al., 2009. Atmospheric carbon dioxide through the Eocene-Oligocene climate transition. Nature (published online 13 September 2009) doi:10.1038/nature08447
This image illustrates long-term changes in yearly surface temperature in and around Antarctica between 1981 and 2007. Places where it warmed over time are red, places where it cooled are blue, and places where there was no change are white.
The map is based on thermal infrared (heat) observations made by a series of National Oceanic and Atmospheric Administration satellite sensors. Because the satellite is observing energy radiated from the Earth’s surface, the image shows trends in skin temperatures—temperatures from roughly the top millimeter of the land, sea ice, or sea surface—not air temperatures.
Letter to Nature 457, 459-462 (22 January 2008) | doi:10.1038/nature07669
Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year
Assessments of Antarctic temperature change have emphasized the contrast between strong warming of the Antarctic Peninsula and slight cooling of the Antarctic continental interior in recent decades. This pattern of temperature change has been attributed to the increased strength of the circumpolar westerlies, largely in response to changes in stratospheric ozone. This picture, however, is substantially incomplete owing to the sparseness and short duration of the observations. Here we show that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported. West Antarctic warming exceeds 0.1 °C per decade over the past 50 years, and is strongest in winter and spring. Although this is partly offset by autumn cooling in East Antarctica, the continent-wide average near-surface temperature trend is positive. Simulations using a general circulation model reproduce the essential features of the spatial pattern and the long-term trend, and we suggest that neither can be attributed directly to increases in the strength of the westerlies. Instead, regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice are required to explain the enhanced warming in West Antarctica.
Two of the authors of the Nature paper comment:
State of Antarctica: red or blue?
A couple of us (Eric and Mike) are co-authors on a paper coming out in Nature this week (Jan. 22, 09). We have already seen misleading interpretations of our results in the popular press and the blogosphere, and so we thought we would nip such speculation in the bud.
The paper shows that Antarctica has been warming for the last 50 years, and that it has been warming especially in West Antarctica (see the figure). The results are based on a statistical blending of satellite data and temperature data from weather stations. The results don’t depend on the statistics alone. They are backed up by independent data from automatic weather stations, as shown in our paper as well as in updated work by Bromwich, Monaghan and others …, whose earlier work in JGR was taken as contradicting ours. There is also a paper in press in Climate Dynamics (Goosse et al.) that uses a GCM with data assimilation (and without the satellite data we use) and gets the same result. Furthermore, speculation that our results somehow simply reflect changes in the near-surface inversion is ruled out by completely independent results showing that significant warming in West Antarctica extends well into the troposphere. And finally, our results have already been validated by borehole thermometery – a completely independent method – at at least one site in West Antarctica (Barrett et al. report the same rate of warming as we do, but going back to 1930 rather than 1957; see the paper in press in GRL).