West Antarctic ice shelf collapse past the point of no return…

26 12 2014
Mark Cochrane

Mark Cochrane

Another guest post from our resident Climate Scientist, Mark Cochrane who has been too busy this year to write much for us… never good news of course, but it’s imperative we stay abreast of the news as the future unfolds.

Two papers now show that the collapse of the Western Antarctic ice sheet is a foregone conclusion. No matter what we do, that ice (equal to 4 m of sea level rise) is going to melt. We can accelerate the rate but we cannot slow it. It isn’t being melted from above, it is being lifted from below, allowing the ice to flow into the sea. There are no remaining impediments (e.g. ridges or mountains) to keep the ice sheet from collapsing completely, so the dominoes are falling whether we like it or not.

One study (Rignot et al. 2014 in Geophysical Research Letters) focused on the observed melting over the last few decades, while the other based their conclusions on computer modeling of the future decay of the ice sheet (Joughlin et al. 2014 Science). Having scientists confirm the same findings using different methods provides confidence that, although the timeline may change a bit, the main results are likely correct. Both studies put the minimum time for this collapse at 200 years, with the maximum time for the collapse being 500 or 900 years, respectively. Best case is a doubling of rates of sea level rise….

While having 200+ years until complete collapse may not sound like an urgent problem, it is. If the West Antarctic ice sheet collapse is certain then most if not all of Greenland will be right on its heels and even portions of the larger East Antarctic ice sheet will be pouring into the oceans. What this means is that not only will sea levels continue to rise, they will continue to rise at increasing rates. Most of humanity lives near the coastlines. We have bequeathed future generations with a legacy of ever shifting shorelines. Many of the world’s largest cities will either have to be abandoned, moved, or protected with massive sea walls that will rapidly become obsolescent as sea levels keep rising. Most goods are shipped by sea meaning that port cities are key. It should be interesting to see how we keep retrofitting docks around the world.

Where is all of this leading us? We have now reached 400 ppm CO2 in the atmosphere. Why is that important?

this level has not been seen on Earth for 3-5 million years, a period called the Pliocene. At that time, global average temperatures were 3 or 4C higher than today’s and 8C warmer at the poles. Reef corals suffered a major extinction while forests grew up to the northern edge of the Arctic Ocean, a region which is today bare tundra. (link)

Since we have no way of removing significant amounts of greenhouse gases from the atmosphere, this is the future that we have programmed into the Earth’s climate system. For those looking for future beach-front property, sea levels were 40 m higher than today. It will take hundreds, if not thousands, of years for all of this to play out so don’t move quite yet! The wildcard in our future will be the weather we experience. CO2 is now rising at about 75 times anything in the geological record so no one really knows what we will experience but chances are that it will not be a good experience in most places. ‘Climate’ is average weather (at least 30 years), meaning that seasons and weather patterns should be roughly stable or bounded over that time period. However, we are now changing the climate continuously so that trying to define ‘average’ weather over several decades doesn’t really make sense anymore than it would to buy your kid’s clothes based on their average height between ages 5 and 15.

Advertisements

Actions

Information

11 responses

26 12 2014
rabiddoomsayer

John Mercer’s prediction is looking better than ever. Is Bradley Opdyke’s conclusion ( http://www.abc.net.au/science/articles/2008/06/25/2283071.htm) so much worse than Than Mark Cochrane’s or are we talking apples and pears?

26 12 2014
mikestasse

Wow….. glad I’m 100m ASL!

27 12 2014
Dr Bob Rich

My concern that none of these predictions look at positive feedback loops from the Arctic methane. All bets are off, and I don’t believe we have 200 years minimum for WAIS to melt. Even the 20 year prediction is only based on local Antarctic considerations. I’d be interested in John’s response.

26 12 2014
John Doyle

Any talk about our adjusting to sea level rise is probably a waste of time. We already don’t have resources to keep our current civilization going for more than a couple of decades at most. Certainly by 2100 we will be beyond needing ports even possibly cities. It may be part of an unknown timeline, but the timeline’s existence is even more certain than icecap melting. It’s the exponential function sending us on our way out.

27 12 2014
pendantry

It might be possible to consider ‘adjusting to sea level rise’ if we were to consider building floating cities — as indeed some are. But you can’t make such things in a period of ‘austerity’.

Correction: the rich buggers can; most can’t.

30 12 2014
Idiocracy

Interesting idea/links pendantry. Though I was gob smacked to read most of theose concepts proclaiming their designs to be “self-sufficient”!!!

TOTAL BS… the inputs would be massive and ongoing, not to mention the maintenance, and just imagine what the registration/insurance would be on a water vessel like that! 😛 Only those on the BRW Rich List could afford those Body Corporate fee’s! 🙂

30 12 2014
pendantry

Cost aside, such constructions would also have a hard time dealing with rogue waves

27 12 2014
pendantry

Well, that’s that, then; Waterworld, here we come.

PS typo alert:
“CO2 is now rising at about 75 times anything in the geological record so no one really knows what we will experience but chances are that it will not be a good experience in most places.”

There’s a problem with ‘… rising at about 75 times anything in the geological record…’ but I can’t parse what you’re trying to say, so can’t suggest a repair.

27 12 2014
mikestasse

It seems obvious to me that it means “75 times as fast as anything in the geological record”…

27 12 2014
pendantry

Of course. My feeble excuse is it’s 5am.

27 12 2014
Dr Bob Rich

I have a correction too. My comment about positive feedback between Antarctic melting and Arctic methane release is directed to Mark, not to John. My feeble excuse is that I am happily writing a new science fiction story while editing a difficult scholarly book.
🙂
Bob

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s