Past increases in sea level

Glass half empty, or glass half full ...

Nature’s reporting of a recent story in the Guardian piqued my interest. It cites a paper that draws attention to the remnants of a 2-kilometre long man-made wall found 21 metres below the surface of the Baltic Sea, which is currently part of the Atlantic Ocean. The finding is pictured below.

The Nature briefing about it says,

“Researchers say the “pristine” discovery was probably used for hunting the Eurasian reindeer more than 10,000 years ago. Before it was submerged by rising sea levels about 8,500 years ago, hunters might have used the wall to force prey into a bottleneck or a nearby lake”.

That depth of 21 metres is interesting.

That submerging was due to the rise of sea levels at the start of glacial melt after the most recent ice age. We know that if all the world’s ice melts, future sea levels will rise by about 80 metres. What we sometimes forget (or at least I do) is that at during the depths of past ice ages, much more water is sequestered in the polar caps than at present. So much in fact, that sea levels at the glacial maxima were sometimes lower than at present by more than 80 metres.

We’re currently a little over halfway between those two extremes. Oceans half-empty, or oceans half-full? A twist on the usual preference.

Those future changes are pretty far-reaching (if you’ll excuse the pun). A big chunk of the current world’s population live less than 80 metres above sea level. Luckily we have time on our hands to migrate future civilisations above that new high tide mark. But perhaps not as much as you might have hoped. Although the time between past glacials and inter-glacials is measured in tens of thousands of years, the ice-melting phase that we’re in now is much faster. Just a few thousand years. Our retreat to higher ground will be a painful and drawn-out incremental experience. Expensive too. A recent press release suggested that Big Oil should be required to pay the 2 billion dollars per year (and rising) cost to New York City. Good idea. But I think it the costs will be a lot more than that. In a few thousand years, only the taller buildings will be poking their heads above the ocean waves. If it were still standing, Trump Tower would be less than 30 stories tall by then. The first 20 floors would be under water. Tower half full, or tower half empty?

In ancient times, before that cited in the Guardian story, any civilizations - if they existed - at all would have been small and primitive. I wonder how many others have been identified - at to what maximum depth below current sea level?

And how deep might the remnants of our ‘civilisation’ be found in another 10 thousand years?