Halting the conveyor

Today we have three stories that are absolutely horrifying in juxtaposition.

The first is a paper that came out a couple of days ago in Nature, describing a study by Jade Bowling (of Lancaster University) et al.  It is an analysis of a strange and sudden change in the topography of the Greenland Ice Sheet that happened in 2014 -- a two-square-kilometer part of the sheet dropped by as much as eighty-five meters.  The question, of course, is what happened to all the ice that used to be underneath it.  And what Bowling et al. found was that it had melted -- that the underside of the Greenland Ice Sheet is riddled with subglacial lakes and rivers.  In this case, downstream of the collapsed region, a flood burst through the surface, and within ten days ninety million cubic meters of fresh water gushed out as the cavity emptied.

We usually think of the melting of the polar ice sheets as a gradual process, something like the way ice cubes slowly melt in your glass of tea in summer.  But what this study shows is that the process proceeds quietly -- until it doesn't.  The tipping point between a gentle trickle and a massive flood can occur suddenly, and be due to factors that are largely out of sight.

The second came out in the same issue of Nature, and has to do with a study of the paleoclimate by a team led by Pedro DiNezio of Colorado University - Boulder.  DiNezio and his collaborators looked at the Atlantic Meridional Overturning Circulation (AMOC), sometimes called the "Atlantic Conveyor."  The AMOC is an enormous ocean current, of which the Gulf Stream is only a part, moving a greater volume of water per second than all of the rivers of the world put together.  It is driven by the combined effects of evaporation (making the water saltier) and cooling as the current flows northward; both of these result in the water becoming denser, and south of Iceland it becomes dense enough to sink.  This draws more warm water northward -- and is why Ireland and the United Kingdom, which are on the same latitude as Alberta, have mild climates.

[Image licensed under the Creative Commons R. Curry, Woods Hole Oceanographic Institution/Science/USGCRP., OCP07 Fig-6, CC BY 3.0]

But freshwater intrusion, like the one the prior study considered, lowers the density of the surface water, eventually making it too fresh to sink.  This can slow down -- or halt entirely -- the AMOC.

The focus of the effects has usually been on northeastern North America and northwestern Europe, where that heat transfer slowdown would be expected to trigger a dramatic cooling similar to the sudden crash that initiated the Younger Dryas 12,900 years ago, during which a warming climate was plunged back into the freezer for over a thousand years.  But what the DiNezio et al. study considered was what happens to all that excess heat.  Just because we here in upstate New York would probably be freezing our asses off doesn't mean the rest of the world would be.  The heat energy, of course, doesn't just go away.

And what they found is that when the AMOC slows down, that heat remains in the tropics -- triggering a spike in temperature and a drop in rainfall near the equator.  "This is bad news, because we have these very important ecosystems in the Amazon," said DiNezio.  "The Amazon rainforest contains almost two years of global carbon emissions, making it a major carbon sink on Earth.  Drought in this region could release vast amounts of carbon back into the atmosphere, forming a vicious loop that could make climate change worse."

But of course, no story about climate change would be complete without some breaking news describing how the Trump administration is determined to make it worse.  Lee Zeldin, head of the Environmental Protection Agency (which should have its name changed to the Big Oil Protection Agency, because under his leadership they couldn't give a flying rat's ass about protecting the environment), has just announced the overturning of a 2009 declaration stating that carbon dioxide and other greenhouse gases endanger human health and welfare.

His justification?  What do you think it was?

"It cost Americans a lot of money," Zeldin said.

The declaration was the foundation of climate change regulation in this country, and the impetus for rules limiting emissions from cars, airplanes, and power plants.  If the "endangerment finding," as the declaration is called, is overturned. it gives corporations carte blanche to ignore previous guidelines and mandates.

Zeldin, of course, thinks this is just hunky-dory.  "This will be the largest deregulatory action in the history of America," he crowed.

Because short-term profit is apparently more in need of attention than the long-term habitability of the planet.

I wish I had a hopeful note to end on, but I don't.  The whole thing puts me in mind of a comment from a student in my Environmental Science class, maybe fifteen years ago.  The question I put to them was, "At what point do you think that the majority of Americans will be motivated to address climate change in a meaningful way?"

Her answer was, "It won't happen until average Americans are directly and harshly impacted by it.  When there's no food on the shelves in the grocery stores.  When the rivers dry up.  When the sea level rises enough to flood major coastal cities.  Until then, it's easier to pretend nothing's wrong."

Another student, aghast, said, "But won't it be too late at that point?"

She responded simply, "Of course it will."

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Ignoring Cassandra

The Atlantic Meridional Overturning Circulation (AMOC), sometimes nicknamed "the Atlantic Conveyor," is an enormous oceanic current that not only encircles the entire Atlantic Ocean, it links up with other circulation patterns in the Indian and Pacific Oceans.

[Image is in the Public Domain courtesy of NASA]

It's called a "thermohaline" circulation because it's driven by two things; temperature and salinity.  Cold water is denser than warm water; salty water is denser than fresher water.  Alterations in these factors determine where the water goes, setting up convection (the movement of a fluid because of gradients in density).  Specifically, as the warm Gulf Stream (the red line along the eastern coast of North America on the above map) moves northward, it cools down and evaporates.  Those both act to increase its density, to the point that just south of Iceland, it sinks.

That sinking mechanism is what drives the entire thing.  Slow that down, and the whole system fails.

Which is exactly what is happening.  A paper last week in Nature found that the AMOC has diminished dramatically because of anthropogenic climate change; the warming oceans, along with fresh meltwater from Greenland, has made large parts of the north loop of the circulation too buoyant to sink.  Since 1950, the flow rate has gone down by 0.46 sverdrups.  Before you say, "Well, that doesn't sound like very much," allow me to point out that one sverdrup is a million cubic meters a second.  The combined flow of all the rivers in the world is only about 1.2 sverdrups.

So 0.46 is huge.

Current models indicate that this change is going to have enormous effects on local climates.  Western and northern Europe are likely to get colder; the surface loop of the AMOC is why Iceland, Scotland, and Scandinavia are way warmer than you'd expect given their latitudes.  The southeastern United States and eastern South America will probably become much warmer; the heat energy doesn't just go away because it's not being transported northward and dissipated.  Rainfall patterns, and storm paths and intensity, will certainly change, but how is unknown.

The truth is, we don't know enough to predict exactly what the outcome will be, at least not with any certainty.  We're perturbing a complex global system with about as much caution as a toddler playing in the mud.  But what seems certain is that we have now entered the "Find Out" phase of "Fuck Around and Find Out."

What kills me is we've been warning about this for decades.  British science historian James Burke's prescient documentary After the Warming described the collapse of the AMOC as an outcome of anthropogenic climate change all the way back in 1991.  But instead of listening to the scientists, and brilliant advocates like Burke who bring science to the public notice, more people were swayed by idiots like former Oklahoma Senator James Inhofe, who brought a snowball onto the floor of the United States Senate and basically said, "Hey, it's snowing, so climate change isn't real, hurr hurr hurr durr."

Of course, listening to Inhofe and his ilk is easy.  If you believe him, you don't have to make any changes to your lifestyle.  And we haven't gotten any further in the intervening decades; President-elect Trump has nominated Lee Zeldin for the head of the Environmental Protection Agency and Doug Burgum for Secretary of the Interior, both thoroughgoing climate change deniers who are deep in the pockets of the fossil fuel industry.  (And please, for the love of all that's holy, stop calling them "climate skeptics."  A skeptic respects the evidence.  These people reject a body of evidence that's as high as Mount Everest in the name of profit and short-term expediency.)

Politicians Discussing Global Warming by Isaac Cordal (2011)

I read a serious analysis of Donald Trump's win claiming that one factor was that Americans have a "suspicion of expertise."  That is something that will never, ever make sense to me.  How is it reasonable to say, essentially, "These people know more than I do, so I don't believe them"?  The result is that we now have one of the most powerful countries in the world being run by a cabal of people who are united by two things -- (1) devotion to Donald Trump, and (2) a complete lack of qualifications.  So this distrust of evidence, science, and rationality is only going to get worse -- and will become the motive force in driving policy.

The problem is, though, if you ignore the truth, sooner or later it catches up with you.  And from the recent paper, it appears it's going to be sooner.  Sea level rise is already threatening coastal communities, and there are island nations that will simply cease to exist if if gets much worse.  Extreme weather events are likely to become commonplace.  We're sure to see alterations in climate that will affect agriculture, and in some places, habitability.

As usual, the people creating the problem aren't the ones who are going to get hurt by it -- at least not at first.  But this is an issue that will, ultimately, affect us all.

And lord have mercy, I am tired.  Tired of shouting warnings, tired of citing study after study, tired of arguing from the standpoint of facts and evidence with people determined not to listen to any of it.  I'm not even an actual scientist, just a retired science teacher and blogger, and I feel like I've been sounding the call about this stuff forever; I can't imagine how the actual researchers feel.  It makes me sympathize with Cassandra, from Greek mythology -- who was blessed with the ability to see the future, but cursed to have no one believe her.

I wish I had some sort of hopeful message to end on, but I don't.  I'm not naturally a pessimist, but given the fact that the country I live in just voted in an anti-science, anti-intellectual, anti-academic administration whose motto seems to be "Corporate Profit Über Alles," I don't think we're going to make any progress here for the next four years.  By then, how much more damage will have been done?

As journalist Sheri Fink put it: "Soon after a disaster passes, we tend to turn our eyes away and focus our resources on the day-to-day, rather than on preparing for the rare, but foreseeable and potentially catastrophic disaster.  It's another form of triage, how much we invest in preparing for that, a very important question for public policy.  But... we are such a short-sighted species."

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Cutting off the circulation

Around 12,900 years ago, the world was warming up after the last major ice age.  Climatologists call it the "Late Glacial Interstadial," a natural warm-up due to the combined effects of the slow, gradual alterations in the Earth's orbit and precession cycle.  But then...

... something happened, and within only a few decades, the Northern Hemisphere -- especially what are now North America and western Europe -- were plunged back into the deep freeze.

The episode is called the "Younger Dryas" event, because the way scientists figured out it had happened was finding traces of pollen in ice cores from a plant, Dryas octopetala, which is only found in cold, dry, windswept habitats.  Areas that had been progressing toward boreal forest, or even temperate hardwood forest, suddenly reverted to tundra.

[Image licensed under the Creative Commons Steinsplitter, Weiße Silberwurz (Dryas octopetala) 2, CC BY-SA 3.0]

There are a number of curious features of the Younger Dryas event.  First, its speed -- climate shifts ordinarily take place on the scale of centuries or millennia, not decades.  Second, the fact that its effects were huge (the average temperature in Greenland dropped by something on the order of 7 C), but were limited in range; in fact, the Southern Hemisphere appears to have continued warming.  And third, after the initial plunge, the system righted itself over the next twelve hundred years -- by 11,700 years ago, the Northern Hemisphere was back on its warming track, and caught up with the rest of the world.

What could have caused such a strange, sudden, and catastrophic event is still a matter of some debate, but the leading candidate is that something halted the Atlantic Meridional Overturning Circulation, sometimes nicknamed "the Atlantic conveyor."  This is the massive ocean current of which the Gulf Stream is only a small part, and which is powered by warm water evaporating and cooling as it moves north, finally becoming cold and salty (and thus dense) enough to sink, somewhere south of Iceland.  This draws more warm water up from near the equator.  But as the Earth was warming during the Interstadial, the ice in the north was melting, eventually making the water in the North Atlantic too fresh to sink, and thus halting the entire circulation.  Some researchers think the process was sent into overdrive by the collapse of an ice dam holding back a massive freshwater lake called Lake Agassiz (encompassing what are now all five Great Lakes and the surrounding region), causing it to drain down the Saint Lawrence Seaway and into the North Atlantic, stopping the AMOC dead in its tracks.  (This point is still being debated.)

What's certain is that the AMOC stopped, suddenly, and took over a thousand years to get started again, plunging the Northern Hemisphere back into an ice age.

Why does this come up today?

Because a new study out of the University of Utrecht has found that our out-of-control fossil fuel use, and consequent boosting of the global temperature and melting of polar ice, is hurtling the AMOC toward the same situation it faced 12,900 years ago.  One of the consequences of anthropogenic global warming might be sending eastern Canada, the northeastern United States, and western Europe into the freezer.

One of the most alarming findings of the study is that climatologists have been systematically overestimating the stability of the AMOC.  It's an easy mistake to make; the current is absolutely enormous, amounting to a hundred million cubic meters of water per second, which is nearly a hundred times the combined flow of all the rivers in the world.  The idea of anything perturbing something that massive is a little hard to imagine.

But that's what happened during the Younger Dryas, and it happened fast.  The new study suggests that if the AMOC does collapse, within twenty years the temperature of Great Britain, Scandinavia, and the rest of northern Europe could see winter temperatures ten to thirty degrees Celsius colder than they are now, which would completely alter the ecosystems of the region (including agriculture).  It would also change precipitation patterns drastically, and in ways we are currently unable to predict.

If you're not already alarmed enough, here's how climatologist Stefan Rahmstorf put it, writing for the site RealClimate:

Given the impacts, the risk of an AMOC collapse is something to be avoided at all cost.  As I’ve said before: the issue is not whether we’re sure this is going to happen.  The issue is that we need to rule this out at 99.9 % probability.  Once we have a definite warning signal it will be too late to do anything about it, given the inertia in the system...  We will continue to ignore this risk at our peril.

The problem is that last bit -- we don't have a very good history of addressing problems ahead of time.  We're much more prone to waiting until things are really awful, at which point they're harder (if not impossible) to fix.  We've let the corporate interests and short-term expediency drive policy for too long; it's increasingly looking like we're close to hitting the now-or-never point.

We need to start electing candidates who take this whole thing seriously.  It is the most important issue of our time.  I try not to be a one-issue voter, but if someone's answer to "What do you intend to do to remediate climate change" is "Nothing" -- or, worse, "Climate change is't real" -- they've lost my vote.

And they should lose yours, too.  For the good of the planet.

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