More than 2.5m Sea Level Rise by 2040?

[marmar]

More than 2.5m Sea Level Rise by 2040?


A warming period more than 400,000 years ago pushed the Greenland ice sheet past its stability threshold (which may have been no more than several degrees above pre-industrial temperatures). This resulted in a nearly complete deglaciation of southern Greenland, raising global sea levels some 4.5-6 meters, found a recent study by Reyes et al. Due to melting elsewhere, global mean sea level then was 6 to 13?metres above the present level. Indeed, melting of the entire West Antarctic Ice Sheet can add a further 6-meter rise in sea levels. If the East Antarctic Ice Sheet (EAIS) were to melt as well, sea levels would rise by around 70 metres.

Sea level is now rising by 3.1mm (0.122 inch) per year. Much of this rise is due to rising temperatures, but there are also other factors. One quarter of the rise results from groundwater depletion, while run off from melting ice and glaciers adds another quarter and the remainder is attributed to thermal expansion of sea water. Furthermore, as temperatures rise, feedbacks start to kick in, e.g. the kinetic energy from stronger waves and more intense storms can speed things up.

Clearly, a rapid multi-meter rise would be devastating as it would flood many coastal cities, as well as much of the land now used to grow food. By how much have sea levels been rising recently and how fast can they be expected to rise in the near future?



Sea levels have risen by some 60 mm over the past 20 years, as above NASA image shows, which has a linear trendline added. The question is whether a linear trendline is the most appropriate trendline, given that it suggests that a similar rise could be expected over the next 20 years. A polynomial trendline appears to fit the data better, as the animation below shows. ...............(more)

The complete piece is at: http://arctic-news.blogspot.com/2014/07/more-than-25m-sea-level-rise-by-2040.html

[muriel_volestrangler]

1. That looks like an unjustifiable extrapolation

You shouldn't just say "can I fit a rough polynomial to this graph" and then extrapolate that well into the future, without some justification for why that particular polynomial is a good model. Note that the blogger hasn't even bothered to tell us what the polynomial is. It smacks of someone who has found a 'polynomial' function on their spreadsheet, without having the faintest idea of what it means. His polynomial showed sea level rise slowing down between 2000 and 2008. Why? If he cannot give reasons for that, he cannot justify a model which later shows sudden acceleration.

[Dreamer Tatum]

2. And the sample is woefully, horribly, misleadingly short

I think we had shorelines before 1993. This is junk statistics.

[muriel_volestrangler]

3. Yes - his polynomial is flat during 1993

and we can't see what it would have modelled before then, but the turn looks suspiciously as if it would have had sea levels falling before then, which isn't what happened in reality, and there would be no justification for saying "forget what happened before 1993 - everything changed that year".

[Dreamer Tatum]

4. So I would accept an extrapolation of at most one year

and even then would attach so many provisos and a wide enough error band to render it worthless.