Likelihood of a large sea level rise by 2100

Post by **kenneal - lagger** » 21 Oct 2015, 18:37

I've been having a "discussion" with Biff recently on the likelihood of large sea level rise before 2100 as predicted by Hanson and was looking at Realclimate.org and found this histogram showing the results of a survey of scientists working in the field of sea level rise. It would seem that over 10% of them feel that a rise in the range of 2000 to 6000 is likely.

Figure 5 Distribution of the experts’ answers to the upper limit of the ‘likely’ range for the RCP8.5 scenario by the year 2100. Many experts consider a global sea-level rise between 1 and 2 meters quite possible in case of unmitigated greenhouse gas emissions. - See more at: http://www.realclimate.org/index.php/ar ... more-18727

Post by **clv101** » 21 Oct 2015, 19:55

We've already discussed how anyone claiming to be taking a scientific or objective approach shouldn't lean to heavily on Hansen's yet to be published paper but this expert elicitation study is worth thinking about.

First of we're assuming RCP 8.5 (+4.5C by 2100, +8C by 2300). That's by no means guaranteed, for example it would require CO2 emissions some three times higher than today by ~2080. By then all the conventional oil, gas and easly extracted coal will be gone - hard to see how we drive the emissions. Not saying it can't happen, just that it's a less than unity probability.

Secondly, they are asked about the 'upper limit' of the 'likely' range. Likely just means > 66% probability. 'Upper limit' means upper limit of what's possible under RCP 8.5, so not only do we have that emission scenario - but also the climate sensitivity is at top end etc. It makes it less likely.

Finally as you point out only 10% of them suggest over 2m. I would suggest the correct interpretation is that it is extremely unlikely (< 5% probability) for sea level rise to exceed 2m by 2100. I think my PhD advisor was one of the 90 surveyed for that paper.

A paper I wrote a couple of years ago was cited in the IPCC sea level rise chapter.

biffvernon · Post by **biffvernon** » 23 Oct 2015, 20:23

With the sea level rise already baked into the system, Miami can only count out its days. But this article's an interesting illustration of the costs of global warming adaptation.

http://www.miamiherald.com/news/local/c ... 41856.html

Post by **kenneal - lagger** » 25 Oct 2015, 05:34

If I had a house there I would be selling up and moving out now before word got round that the houses will be worthless in a few years time! I wouldn't touch anything less than 10 metres above sea level, unless built on solid rock, because with storm surges and erosion anything below that could go at anytime soon. If it was built on solid rock I might be persuaded by something special if it was 6 metres above sea level.

Post by **kenneal - lagger** » 31 Mar 2016, 03:55

The science is gradually tipping towards fast sea level rise. Drastic' Antarctic melt could double global sea-level rise

The modelling assessment says that Antarctic melting alone could contribute more than a metre to sea level by the end of this century.

And that doesn't include the Arctic. All the factors included in this new model could apply to the Arctic as well so estimates from there could yet increase.

I think it's always worth listening to what Hansen has to say. He's been pretty correct thus far.

Post by **clv101** » 31 Mar 2016, 07:27

I think this post on the Hansen paper is useful:
http://icarus-maynooth.blogspot.co.uk/2 ... et-al.html

johnhemming2 · Post by **johnhemming2** » 31 Mar 2016, 08:18

kenneal - lagger wrote: And that doesn't include the Arctic. All the factors included in this new model could apply to the Arctic as well so estimates from there could yet

Why would the floating arctic ice be an issue?

Post by **kenneal - lagger** » 31 Mar 2016, 13:54

Greenland and its land based ice is in the Arctic and is the issue. Sorry! I shouldn't assume a degree of knowledge in my readers.

biffvernon · Post by **biffvernon** » 31 Mar 2016, 14:02

A massive rise in sea level is coming, and it will trigger climate chaos around the world. That was the message from a controversial recent paper by climate scientist James Hansen. It was slated by many for assuming – rather than showing – that sea level could rise between 1 and 5 metres by 2100.

But now, just a week after being formally published, it is being backed up by another study. “He was speculating on massive fresh water discharge to the ocean that I don’t think anybody thought was possible before,” says Rob DeConto of the University of Massachusetts Amherst. “Now we’re publishing a paper that says these rates of fresh water input are possible.”

DeConto’s findings suggest that even if countries meet the pledges made as part of the UN climate agreements in Paris last year, global sea level could still rise 1 metre by 2100. If emissions keep climbing it could go up more than 2 metres. North America would be especially hard hit, because gravitational effects mean that ice loss from Antarctica will lead to bigger local increases for the US East Coast.

“Today we’re measuring global sea level rise in millimetres per year,” DeConto says. “We’re talking about the potential for centimetres per year just from [ice loss in] Antarctica.”

https://www.newscientist.com/article/20 ... evel-rise/

https://theconversation.com/what-does-t ... rise-56807

Post by **kenneal - lagger** » 31 Mar 2016, 15:10

Thanks for that, Biff. Although Hansen's predictions are on the high side the science is moving in his direction and, given that science tends towards the conservative, it is no surprise to me.

All the IPCC predictions in the past have been exceeded in following reports and this is just another one of those as the science moves forward.

emordnilap · Post by **emordnilap** » 31 Mar 2016, 15:56

Can someone provide a link to reliable data showing sea level rises over the past few decades, please?

johnhemming2 · Post by **johnhemming2** » 31 Mar 2016, 17:54

kenneal - lagger wrote:Greenland and its land based ice is in the Arctic and is the issue. Sorry! I shouldn't assume a degree of knowledge in my readers.

It was not clear from what you said. Normally people refer to the sea ice. I accept entirely that what happens in Greenland is critical to sea levels although the Antarctic has potentially up to ten times the effect.

Post by **kenneal - lagger** » 31 Mar 2016, 18:56

When I am referring to sea level rise I am always referring to land based ice unless I am making a specific point about sea ice not making any difference apart from albedo effects. I agree about Antarctica though but that would be over a much longer term than Greenland.

biffvernon · Post by **biffvernon** » 31 Mar 2016, 22:39

emordnilap wrote:Can someone provide a link to reliable data showing sea level rises over the past few decades, please?

Just shy of 3mm per year on average.
Not all places are average.

biffvernon · Post by **biffvernon** » 31 Mar 2016, 22:42

johnhemming2 wrote: It was not clear from what you said. Normally people refer to the sea ice. I accept entirely that what happens in Greenland is critical to sea levels although the Antarctic has potentially up to ten times the effect.

Some of the Arctic ice is not on Greenland but on Baffin Island and other such chilly lands.