The issue of rising sea levels came back into national focus last week when one of our presidential contenders used the matter as a laugh line before a throng of cheering supporters. He recalled that his opponent had vowed to take action to stem rising sea levels, pausing with a perplexed grin, as the laughter grew to a raucous crescendo. Obviously, many Americans aren't very worried.
The event rekindled my interest in the topic. Two years ago, I read a fascinating book by Duke University’s Orrin Pilkey: The Rising Sea. Pilkey, seen by many as the dean of America’s coastal scientists, urged city planners in 2009 to plan on seven feet of sea level rise on U.S. coasts by the end of the century. That would essentially eliminate beachfront development anywhere in the East.
But with the passage of several years, I figured there must be plenty of new material. There was. I settled on a $3.00 eBook offering by Daniel Grossman, a National Geographic editor, titled Deep Water: As Polar IceMelts, Scientists Debate How High Our Oceans Will Rise.
I liked "Deep Water." In a few short hours of reading, Grossman guides the reader through the messy business of real scientific research: geologists and geochemists negotiating the challenges of hungry Hudson Bay polar bears, temperamental Australian rental vans and competing scientific specialties (and egos) to get to the bottom of genuine controversies.
In this case, the controversy was whether current levels of global warming should be expected to raise global sea levels by 62 feet, or perhaps only 31 feet, the consensus view supported by most geochemists. The search for the answer takes the reader to Southwest Australia, Bermuda, the Bahamas, Boston and New York.
In a nutshell, much is already understood about ice ages and interglacial warm periods in the distant past: how warm or cold they were; how much CO2 was in the atmosphere at the time; and the advance and retreat of ice sheets – among many other features. Two warm periods, however, deserve special attention: the one preceding the last ice age 125,000 years ago (clumsily named “Stage 5e”), and one dated about 400,000 years ago (“Stage 11”). These two “interglacials” are thought to be the hottest times on earth for several millions of years – but only 1 degree Fahrenheit hotter than the world is today.
Scientists generally agree that much of both the Greenland and West Antarctic ice sheets melted during these two stages, raising global sea levels about 30 feet above where they are today. But geologists have recently found unmistakable signs of ancient fossil seashores dating back to Stage 11 in the geologically-stable regions of the Bahamas and Bermuda. And here’s the problem: those features are more than 60 feet above today’s sea levels.
Did sea levels rise more than 60 feet in these warm stages? If so, the implications are serious: The massive East Antarctic ice sheet had to have been aroused, in addition to the somewhat smaller Greenland and West Antarctic sheets. And while Stages 5e and 11 were slightly warmer than today, our era will bypass them both during this generation, with no end to heating in sight, due to our much higher levels of atmospheric greenhouse gases, and continued inaction on curbing emissions.
In the end, it looks like 31 feet of additional sea level rise for Stages 5e and 11 is the more probable estimate. (Find out why for yourself!) But the journey is well worth the read, and I recommend that you follow the thread for yourself.
I should add that it’s not just idle curiosity driving these researchers. If we manage to stabilize the climate by significantly reducing greenhouse gases in our lifetime, there’s a good chance that sea levels will again peak at about 31 feet above where they are today. If we don’t, then then it's more likely that East Antarctica will also get in on the melting. We can only speculate at what that might mean. But even the lower level of 31 feet would inundate 25% of the U.S. population, according to the U.S. Geological Survey.
And at the higher levels? Nobody wants to think about that, not even me.
Thanks for caring about this, and may God bless you.
More images related to sea level science:
|USGS map of new coastline at 30' rise|
|Fossil beaches: Wave-cut terraces on geologically-unstable San Clemente, CA|