Ice melt, sea level rise and superstorms: Hansen on his magnum opus

Why ice sheets may melt faster than expected, and what that could mean for our near future

In this video Jim Hansen provides a “video abstract” of his latest — and longest — paper, Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous, published this week after a lengthy period in review. He, and his stellar list of co-authors, have also provided an “abbrievated” version of the paper, which I strongly recommend you read.

My abstract is a bit shorter: fresh water from melting ice sheets in Greenland and Antarctica is beginning to change the way that heat moves around in the global ocean, setting up feedbacks that will melt the ice faster. This in turn will lead to much more rapid sea level rise than suggested in the recent IPCC report, and much bigger temperature contrasts between warm and cold oceans in the North Atlantic and around West Antarctica — which will drive the mid-latitude superstorms of the paper’s title.

Not a pretty prospect. And if you think it’s unlikely, consider this. There are already “cold blobs” in the North Atlantic and off West Antarctica, Atlantic storms are becoming much more vigorous , and there are hints of an acceleration in the rate of sea level rise.

Hansen has been right before. I hope, for all our sakes, that this time he’s not.

Postcards from La La Land: Wishart falls through Thin Ice

ThinIceAllow me to pose a question. Which fearless investigative reporter, magazine publisher and author could be bothered to attend a school showing of Thin Ice, the excellent climate documentary put together Simon Lamb and scientists from VUW and Oxford? And did he stand up at the end and make a fool of himself? Well, by his own admission he stood up and asked questions. Whether he made a fool of himself is another matter, but there’s some handy evidence we can look at…

Any New Zealand reader with a passing interest in climate issues will know that I’m talking about Ian Wishart, a writer with an extensive track record of misunderstanding climate science and a tendency to shout about it from the rooftops. Last week he published a “review” of Thin Ice at his Investigate Daily web site. It was also picked up at µWatts. In this “review” he provides all the evidence we need to decide on his expertise.

Continue reading “Postcards from La La Land: Wishart falls through Thin Ice”

Totten hots up, ice shelves melting: it’s grim down south

AntarcticaCryosat2Much news in recent weeks from Antarctica, and none of it good. An Argentinian base on the tip of the Antarctic Peninsula recently reported a new high temperature record for the continent — 17.5ºC. A team of scientists has discovered that East Antarctica’s Totten Glacier — which drains a catchment that contains enough ice to raise sea levels by 3.5 metres — is vulnerable to melting caused by warm ocean water lapping underneath the ice and reaching inland1. Another group has stitched together satellite data on ice shelf thickness gathered from 1994 to 2012 and found that the ice shelves — mostly stable at the beginning of the period, are now losing mass fast2. From the abstract:

Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 km3 per year for 1994-2003 to rapid loss of 310 ± 74 km3 per year for 2003-2012. West Antarctic losses increased by 70% in the last decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades.

The Amundsen region is home to the Pine Island Glacier, notorious for its current rapid loss of mass, and probably already past the point of no return for long term total melt. The map below shows the big picture: large red dots are ice shelves losing mass. Blue dots are shelves gaining mass.

Antarcticiceshelves

Ice shelves are important features of the Antarctic cryosphere. They buttress the ice piled up on the land, slowing down the flow of ice into the ocean. As the shelves lose mass, the flow of ice from the centre of the continent can speed up, adding to sea level rise. There’s a very good overview of the process — and the findings of the Paulo et al paper — in this excellent Carbon Brief analysis.

The study of the Totten Glacier — one of the fastest thinning glaciers in East Antarctica — is the first to look at the detail of the sea floor and ice thickness in the area. The study finds that there are “tunnels” under the ice leading into a deep trough inland that cold convey warm water inland — the same process that has destabilised the Pine Island Glacier in West Antarctica. As the authors suggest, rather drily, “coastal processes in this area could have global consequences”.

These signs of rapid changes around the coasts of Antarctica, together with hints that large parts of the huge East Antarctic ice sheet are at risk of following West Antarctica into the sea, suggest that even if sea levels only rise by a metre by the end of this century as the IPCC projected last year, the longer term picture will be a great deal wetter than that. After all, there is the equivalent of 60 metres of sea level rise locked up in East Antarctica.

For a very good overview of the state of our understanding of what’s going on in Antarctica, I recommend a listen to VUW’s Professor Tim Naish being interviewed by Radio New Zealand National’s Kim Hill last Saturday. Naish even covers what’s happening to the sea ice down there, but a longer term study of the sea ice is getting under way, led by another VUW prof — Jim Renwick.

  1. Greenbaum JS et al, (2015), Ocean access to a cavity beneath Totten Glacier in East Antarctica, Nature Geoscience, doi:10.1038/ngeo2388 []
  2. Paolo, F.S. et al, (2015), Volume loss from Antarctic ice shelves is accelerating, Science, doi/10.1126/science.aaa0940 []

TDB today: Goodbye coastline – we are beyond the point of no return

In which I pull together the strands of the recent bad news from Antarctica and Greenland, and lament the loss of the coastline we all grew up with — no longer a theoretical possibility but a long term certainty. Check out Goodbye coastline – we are beyond the point of no return, this week’s post at The Daily Blog, and start planning for all our watery futures.

PIG and pals pass point of no return – West Antarctic ice melt inevitable

Two new papers published this week suggest that the West Antarctic glaciers draining into the Amundsen Sea — the Pine Island, Thwaites, Haynes, Pope, Smith and Kohler glaciers — are melting rapidly and are now committed to collapse, adding up to 1.2 metres to future sea level rise. In the NASA JPL video above, Eric Rignot, lead author of a paper1 examining how the glaciers’ “grounding lines” — the point where the bottom of the glacial ice leaves the bedrock and starts to float — have retreated very significantly over the last 20 years explains how they are now melting back unstoppably. Another paper modelling ice loss from the Thwaites glacier 2 finds that it is committed to retreat and collapse via the same mechanism. Lead author Ian Joughin of the University of Washington, told Science magazine:

The next stable state for the West Antarctic Ice Sheet might be no ice sheet at all…

Continue reading “PIG and pals pass point of no return – West Antarctic ice melt inevitable”

  1. E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl. Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011. Geophysical Research Letters, 2014; DOI: 10.1002/2014GL060140 []
  2. Ian Joughin, Benjamin E. Smith, Brooke Medley. Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Science, DOI: 10.1126/science.1249055. []