A warmer Arctic

Every school child learns that the Earth’s oceans cover roughly 3/4 of the planet’s surface, but what most of us don’t realize is that just 8 percent of that area covers the continental shelves — and that area provides 75 percent of all global fish catches — this I just learned from Callum Roberts’ excellent book, “The Unnatural History of the Sea,” which documents how we’ve been busily depleting fish stocks since our ancestors climbed down from the trees and figured out how to make hooks and toss them into the water. The whole book is an eye opener about how looking at past fisheries data tells us how much we have lost — and how we have to work even harder to protect what we have.

But the real reason I wanted to post this post was to observe, as Roberts does, that 87 percent of the area of the ocean is more than 1,000 meters deep — and for oceanographers interested in understanding how changing climate will change currents, this is where a lot -but not all — of the action is. And like the sleuthing that’s reported in Callum Roberts’ book,  scientists are piecing together how the ocean’s currents will work in a warmer world by looking at the past.

Andreas Born, a German who has just defended his PhD at the University of Bergen in Norway,  been looking at what has happened in the Eemian interglacial 126,000 years ago, before last ice age. It was warm then, and some scientists say this might be an example of the kind of  warmer climate we can expect. But unlike now, the Earth overall was cooling, especially in the Arctic, as the ice age came on. Long story short, the northern extension of the Gulf Stream, the North Atlantic Current, shifted farther north and carried warmer subtropical waters to northern Europe. So while the Arctic overall was cooling (and those glaciers were starting to rumble out of northern Canada towards the US) the warm currents kept Scandinavia ice sheet free for several millennia.

So what happens if the Arctic is actually warmer? Born predicts that as the sea ice cover shrinks, circulation in the subpolar region, called the subpolar gyre, will strengthen. That will essentially block the North Atlantic Current from bringing its warm waters up to Scandinavia.

Surface waters or deep waters?

What’s interesting about this prediction is that Born is essentially saying that surface currents will control the transport of warm Atlantic water into the Arctic — which is a little different than what a whole slew of researchers are looking at when they look at the Atlantic Meridional Overturning Circulation, which is a big conveyor belt of water that moves north on the surface of the Atlantic  until it reaches the Arctic, then cools, plunges and heads south as deep water. One of Born’s colleagues at the Bjerknes Centre, Svein Østerhus, is looking at the movement of this deep water, as I described in a piece on ScientificAmerican.com.  His pursuits include looking at the formation of the deepest coldest water in the world, in the Antarctic in the Weddell Sea. But more about that in a subsequent post.

This just in on the geoengineering front in the battle to grapple with climate change: At least as far as controlling sea level rise, it won’t work. A study just published in the Proceedings of the National Academy of Sciences warns that we’re in for at least 30 cm of sea level rise by 2100 “despite all but the most aggressive geoengineering under all except the most stringent greenhouse gas emissions scenarios.”

Aggressive geoengineering, in this case, means injecting sulfur dioxide into the atmosphere at a rate comparable to a Mount Pinatubo eruption every 18 months (!) or building an ever expanding fleet of giant space mirrors.

The “business as usual” scenario has sea-levels rising by 1 meter by 2100 — enough to flood out 150 million people and swallow roughly 10 percent of the “global gross world product.”

The graphic of the Greenland Ice Sheet melt is courtesy of Konrad Steffen and Russell Huff, CIRES, University of Colorado at Boulder. They have done some chilling work (pardon the pun) on the melting of this enormous ice sheet.

One of the things that really got me interested in the question of how ocean currents will affect future climate is a report by the US Global Change Research Program (USGCRP*), called Abrupt Climate Change. One of my sources told me to read Ch. 4, entitled “The Potential for Abrupt Change in the Atlantic Meridional Overturning Circulation.” For those of us who like to state things dramatically, this is kind of stuff that Hollywood loves — yep, think, “The Day After Tomorrow”:

Now, anyone reading this blog probably knows that this movie took a couple of scientific facts and blew them way out of proportion. As George Monbiot says in The Guardian, “it was a great movie and lousy science.” Nevertheless, it did bring attention to the idea that changing ocean currents could and will affect our climate.

But first, what is the Atlantic Meridional Overturning Circulation — abbreviated AMOC — anyway? It’s not, as many people have said, the Gulf Stream (which is mainly wind driven, as it happens). But it is a kind of giant conveyor belt of heat and salt that cycles in the Atlantic, with a northward flow of warm salty water in the upper layers of the Atlantic, traveling from the Equator to the poles, and then a southward flow of colder water in the deep Atlantic.

One important feature of this circulation is the warm water that comes up to the Arctic and cools off, releasing heat. As the water gets colder, it gets denser and then sinks. It then flows south towards the Equator. That sinking helps pull the warm water up from the Equator. It’s kind of like a perpetual motion machine in the ocean, driven by imbalance between the heat of the sun coming in at the Equator compared to the relative coolness at the poles. Simple, right?

Here’s a picture from Wikipedia that shows how it works:

There are many things that are interesting about this movement of the ocean’s currents, one of which is that scientists still aren’t completely sure about the relative importance of all the physical forces that makes it work. (!)

Yes, it’s winds, and tides, and the buoyancy of warm salty water that then becomes cold dense water, with a dash of heat added at the bottom of the ocean by from the warmth of the earth’s core, but essentially, we don’t really know how if we change one component (for example, if the poles get warmer), how ocean currents will react.

So that brings me back to the Potential for Abrupt Climate Change and the Atlantic’s circulation.
First of all, while we don’t know exactly how all the forces that drive the Atlantic’s circulation work, we do know that doing anything to change the circulation will have a big effect.

We know because we have pretty solid evidence for this in paleoclimate records. These changes include “changes in African and Indian monsoon rainfall, atmospheric circulation of relevance to hurricanes, and climate over North America and Western Europe,” according to Ch. 4 of the USGCRP report.

Based on this, the report goes on to say that scientists don’t think that it will stop, although it will slow down. Here’s science speak for that “No current comprehensive climate model projects that the AMOC will abruptly weaken or collapse in the 21st century.” Whew, so Hollywood DID get it wrong — no icebergs in the East River after all!

But wait… if the Atlantic’s circulation were to collapse, forget about icebergs in the East River, we’re talking almost three feet of sea level rise, and to quote the report, this 80 cm of sea level rise would be in addition to “what would be expected from broad-scale warming of the global ocean and changes in land-based ice sheet due to rising CO2, changes in atmospheric circulation conditions that influence hurricane activity, a southward shift of tropical rainfall belts with resulting agricultural impacts, and disruptions to marine ecosystems.” What would 80 cm of sea level rise look like in Manhattan? Found this great image on geology.com:

Looks like Wall Street gets wet feet.

But as the report writers state, this is very unlikely.

Of course, what is very unlikely? That’s the kicker, I think. And you have to wade through quite a bit of this report until you find out that very unlikely is 10 percent. TEN PERCENT.

And that is why there are some two dozen monitoring efforts across the Atlantic, trying to get a handle on how the AMOC works, and why scientists are pushing to set up a comprehensive, coordinated international program to figure it all out. More about that next time.

*Since this is a blog, I get to interject all kinds of personal observations, like this one: Am I the only person out there who looks at this acronym and thinks immediately of the CRP and the Watergate Plumbers? I know it’s not exactly the same, and I guess I am showing my age, but I can’t help but see that acronym and think about Nixon.

With the shrinking of the polar ice caps, places like the Arctic Ocean and the Barents Sea are attracting more attention from shippers, oil companies and the like. In recognition of this (and partly to explore the region to let out oil and gas leases on the Norwegian Continental Shelf), the Norwegian government has been funding this enormous mapping and exploration project in the Barents Sea, called the MAREANO project.

Since their first mapping year in 2006, the project has discovered cold water coral reefs,
photographed marine life at a depth of 2700 meters and documented the effects of trawling on marine life on the Barents Sea bottom.

There’s an impressive collection of pictures on this site, which should disabuse anyone of the idea that the cold waters of the Barents Sea are barren. They’re not. The shrimp pictured at the top of this post is from 2700 meters, and then there’s this jellyfish that no one has ever identified before from 1000 meters. You can also create your own maps showing areas where there are vulnerable natural resources and the like.

All of this info feeds into the Norwegian Management Plan for the Barents Sea, and may also play a role in future CO2 management — one study of the North Sea, the Norwegian Sea and in the Southern Barents Sea estimated the storage capacity of these areas, in the depth interval 0.8-4 km below sea level, at about 13 Gt (that’s 13 000 000 000 tons for people like me who don’t think in gigatons) CO2 in geological traps (outside hydrocarbon fields), while the storage
capacity in aquifers not confined to traps is estimated to be at least 280 Gt CO2.