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Ice Sheets and Sea level: what past climate change tells us is likely
Paleoclimate shows us that sea level rise could become catastrophic with rises of 3 feet per 20 years seen as possible. "We are still potentially underestimating the instability of the ice sheets" informs Stefen Rahmstorf, Professor of Physics of the oceans from Postdam University in a video interview. "The IPCC has greatly revised it's estimates of how unstable the Greenland ice sheet was."
The video by Peter Sinclair and the Yale Forum on Climate Change and the Media shows a number of climate scientists interviewed discussing sea level rise, ice sheet collapse and past examples in paleoclimate history.
Climate scientist Dr Richard Alley from Penn State University in a graph illuminates us that on current CO2 levels we can expect sea level rise to impact 10 per cent of the Earth's population, hundreds of millions of people. He says in the video that "Greenland is very tightly tied to temperature, and if it gets too hot, it goes away".
Research published in March 2012 showed that the Global Warming threshold for Greenland Ice Sheet collapse is about 1.6 degrees C, although we may be seeing the start right now. The researchers said "We estimate that the warming threshold leading to a monostable, essentially ice-free state is in the range of 0.8-3.2 °C, with a best estimate of 1.6 °C".
The lower end of that range is where we are now, and due to inertia in the climate system we have the same amount of warming in the pipeline. So we are probably aleady committed to disintegration of the Greenland Ice Sheet.
"Too hot is not too many degrees from where we are now", said Dr Alley.
Arctic and Antarctic warming linked
Down at the bottom of the world, Antarctica is also showing signs of big changes in ice mass loss. Michael Studinger from NASA Operation Ice Bridge says "The ice sheets, for example like Pine Island Glacier (PIG) are rapidly thinning. And the thinning is rapidly accelerating and it is spreading further and further inland."
In Antarctica warmer ocean currents appear to be a primary driving force for destabilizing ice sheets as they eat away at the ice shelves that restrain the large ice streams like the Thwaites, Pine Island Glaciers and other ice streams around the continent.
Latest research published 11 December 2013 in Global and Planetary Change by S.Jevrejevaa et al in a paper titled Trends and acceleration in global and regional sea levels since 1807 shows that global sealevel rise is accelerating at rate of 0.02 ± 0.01 mm/yr (1807–2009) with the Fastest sea level rise in Arctic (3.8 mm / yr) and Antarctica (3.5 mm / yr).
Paleoclimate shows how fast ice sheets can collapse raising sea levels
James Hansen highlights that the last time atmospheric temperatures were 2 to 3 degrees warmer, sea levels were 25 metres higher. With great inertia in the earth's climate system, We are stretching the elastic which will rebound to a new sea level with devastating consequences. Scientists have estimated that at slightly above current temperatures we are about 20 metres below what the sea level equilibrium should be.
Two years ago in a press conference at the American Geophysical Union Fall meeting 2011 in San Fransisco climate scientists James Hansen, Ken Caldeira and Eelco Rohling explained that the climate sensitivity may be greater than previously thought with the paleoclimate record pointing towards potential rapid climate change.
The data range on the rate of accelerating mass loss is still too short to determine whether ice sheet mass loss will follow a somewhat linear path, or an exponential path doubling every 10 years or shorter time period. If it's the later, we may face massive sea level rises later this century, according to a December 2012 discussion paper by James Hansen
Link between Arctic and Antarctic warming periods
The East Antarctic Ice sheet which sits on a high plateau was also much smaller and probably contributed 10 metres to sea level rise. Lead researcher Carys Cook was interviewed in the Sinclair video. The research was published in Nature Geoscience in July 2013 as Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth (abstract). From the abstract:
"The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene."
Carys Cook described that the East Antarctic ice sheet must have retreated several hundred kilometres inland. She described the implications for sea level in the interview with Peter Sinclair:
"There was no ice on Greenland and that accounts for about 5 metres of sea level. The West Antarctic Ice sheet as well was probably gone and that accounts for about 5 or 6 metres of global sea level. The retreat from the East Antarctic Ice sheet gave an extra 10 metres of global sea level. So in total we are looking at between 20 and 22 metres higher than they are today."
Peter Sinclair also gives us a clip of James Hansen in 2009 explaining: "Now that wouldn't happen instantly, but we could get several metres of sea level rise in one century. In fact the last time ice sheets disintegrated was 14,000 years ago when sea levels went up 20 metres in 400 years. So that is one metre every 20 years."
The Pliocene was also much warmer in the Arctic, with extreme warm periods, as Geology ProfessorJulie Brigham-Grette explains in the video. You can watch a July 2012 24 minute Youtube presentation by Brigham-Grette on Lake El' gygytgyn Research in Siberia.
These extreme warm periods in the Arctic also correspond with warm periods in Antarctica. Brigham-Grette, the lead U.S. scientist said in a media release July 2012:
“What we see is astonishing. We had no idea that we’d find this. It’s astonishing to see so many intervals when the Arctic was really warm, enough so forests were growing where today we see tundra and permafrost. And the intensity of warming is completely unexpected. The other astounding thing is that we were able to determine that during many times when the West Antarctic ice sheet disappeared, we see a corresponding warm period following very quickly in the Arctic. Arctic warm periods cluster with periods when the Western Antarctic ice sheet is gone.”
Brigham-Grette's team examined in detail four warm phases; two of the oldest warm interglacials from about 1.1 million years ago and 400,000 years ago, and two of the youngest from 125,000 and about 12,000 years ago.
Peter Sinclair's video ends with a video interview with Brigham-Grette in which she says,
"The value of our record is looking at the fact that the Arctic can become very quickly as warm, and that warmer environment is reaching a point where increasing melt of places like Greenland and the West Antarctic Ice Sheet are almost inevitable."
Creation stories remember significant sea level rise 14,000 to 12,000 years ago
Here in Australia we have memories of that last significant rise in sea level between 14,000 and 12,000 years ago when the land bridge between mainland Australia and Tasmania was flooded along with areas of Port Philip.
The memories are preserved in the oral and spiritual traditions of the Australian first peoples in the Kulin nation of southern Victoria. Oral history and creation stories from the Wada wurrung, Woiwurrung and Bun wurrung languages from around present day Melbourne describe the flooding of Hobsons Bay and Port Philip, once a productive kangaroo hunting ground. Creation stories describe how Bunjil was responsible for the formation of the bay, or the bay was flooded when the Yarra river was created (Yarra Creation Story.)
While sea level rise is inevitable and now unstoppable, Federal and State Governments in Australia are withdrawing from co-ordinated coastal planning leaving this responsibility more and more to local municipal councils.
What will our new stories say if sea level rises again at the rate of a metre every 20 years resulting in the wholesale dereliction and abandonment of coastal housing and infrastructure?
How will we deal which the mass migrations of people? Will Prime Minister Tony Abbott's slogan of Stop the Boats still be parroted?