Catastrophic Sea Level Rise within Three Generations

[muriel_volestrangler]

22. Again, no doubling period has been 'established' for sea level rise

It has not been established that it's exponential. Hansen suggested it might be, a couple of years ago, but didn't know if it's 5 or 10 years, and said it wouldn't last as exponential. There is evidence the glacier melting is speeding up. There's not enough data to show it's exponential - we see that in 2014 the Greenland mass balance was steady. We're trying to work off just a few years' observation. Extrapolating that as exponential over 55 years is unreasonable.

"We have already locked in roughly 70 meters of SLR"? Where have you pulled that from? That's a bit more than the complete melting of all of Greenland and all of Antarctica would produce (6m + 60m). On your blog you talk about Jason Box's reference to 69 feet of sea level rise for the CO2 level in the atmosphere we now have - are you confusing feet and metres? 'Irreversible' does need to be considered, though - in the talk Box gave, he points out that part of the problem with Greenland is that if a certain amount of the ice on it slumps to lower altitudes, then the change does mean only a new cold period could stop all the melting to that equilibrium level; but if we did lower the CO2 before then, we might avoid getting to the historic equilibrium point (which is where the 69 feet figure comes from). And he says people really don't know how fast sea level rise might happen; he suggests up to 6 feet by 2100, which, again, is a lot different from 7 metres in 55 years.

Looking through the several links in your post, all I can find is a mention of the historical meltwater pulse 1A of 14,000 years ago in this one: http://earlywarn.blogspot.co.uk/2012/01/hansen-still-argues-5m-21st-c-sea-level.html . That's not talking about a meltwater pulse like one we've had recently that caused a disruption of ocean currents; it's saying the pulse was the melting of glaciers, far more rapidly than what we're seeing now. It's saying melting can be non-linear, not that it's the same situation we have now (after all, that was exiting a glacial period). And how does that blog post end?

I take Hansen's opinions very seriously. It's certainly true that there isn't enough data to rule out this scenario yet (though another decade of data should help a lot). Obviously at this point he hasn't succeeded in persuading most of his colleagues, but neither have they persuaded him. Only more data is likely to resolve the situation.

This is what I've been saying, all through this thread: we don't have enough data to make any decent prediction about an exponential sea level rise.