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Abrupt Climate Change -- How Bad Could It Be?

thedayaftertomorrow25.jpgIf global warming results in the "abrupt climate change" scenario of a "little ice age" in the Northern Hemisphere, just how bad might it be? A couple of new studies take a look at the paleogeological evidence to find out.

Although the idea of global warming triggering an ice age may be couter-intuitive, the science is pretty solid. Melting icepack in Greenland results in the dumping of large amounts of fresh water right into the path of the North Atlantic warm water flow, resulting in the slowing and eventual cut-off of the circulation; this, in turn, results in lower temperatures in parts of the Northern Hemisphere, with Europe likely to be hit the hardest. Such a pattern has happened in the past due to the slower natural cycles of global temperatures; the fossil and ice core evidence suggests that the shift from a warm, wet environment to a cold, dry climate could take place over a matter of a few years.

Recent findings that the warm water flow may, in fact, be seeing a dramatic reduction has turned this concept from a theoretical possibility to a very real threat. But what would that world look like? Two studies give us very different images of what might happen.

Climate scientists at the Goddard Institute for Space Studies have been able to use a new model of ocean-atmosphere interaction to reproduce the effects of a massive freshwater dump into the North Atlantic that happened 8,000 years ago. The models results closely matched the geological record, and gave researchers new insights into the effects of a thermohaline circulation drop-off.

The researchers prodded their model with a freshwater pulse equal to between 25 and 50 times the flow of the Amazon River in 12 model runs that took more than a year to complete. Although the simulations largely agreed with proxy records from North Atlantic sediment cores and Greenland ice cores, the team's results showed that the flood had much milder effects around the globe than many people fear--including the dramatic shifts in climate depicted in the 2004 movie 'The Day After Tomorrow'.
According to the model, temperatures in the North Atlantic and Greenland showed the largest decrease, with slightly less cooling over parts of North America and Europe. The rest of the northern hemisphere, however, showed very little effect, and temperatures in the southern hemisphere remained largely unchanged. Moreover, ocean circulation, which initially dropped by half after simulated flood, appeared to rebound within 50 to 150 years.
"This was probably the closest thing to a 'Day After Tomorrow' scenario that we could model," said LeGrande. "The flood we looked at was even larger than anything that could happen today. Still, it's important for us to study because the real thing occurred during a period when conditions were not that much different from the present day."

So here's one end of the potential impact spectrum: a minor temperature drop, with ocean circulation disruption lasting no more than a century and a half (a blink of the geological eye). This would be a problem, to be sure, but not the global civilization-disrupting event seen in some scenarios. Unfortunately, other research suggests that a far worse result is also possible.

Flavia Nunes and Richard Norris, oceanographers at the University of California, San Diego, have produced an article for Nature describing the "Palaeocene/Eocene Thermal Maximum" (PETM) event of about 55 million years ago, during which ocean temperatures shot up by 7 or 8 degrees C, followed by a rapid change in ocean circulation. The Atlantic circulation saw a disruption of flow lasting a couple of thousand years, then a reversed flow that took 100,000 years to correct. The implication is that a major thermohaline circulation disruption would not be a brief event, but an extremely long-term problem.

Although scientists have found evidence of similar links between ocean current and climate in the last 200,000 years, [Woods Hole oceanographer Karen] Bice says that the PETM is a much better analogue for the climate change we see today, because it occurred in a world that was warming gradually in response to rising greenhouse gas levels. [...]
"It's a good indicator of what could happen in our own future," warns Bice.

It's notable that the PETM conditions are not known to have triggered an ice age. This is likely because the temperature increase was sufficiently dramatic as to melt the undersea methane clathrates, which in turn released a sufficient level of greenhouse gas to keep the global environment quite warm for potentially millions of years.

So which is it? Hopefully, the first scenario is the more accurate reflection of the current environment; the second scenario, with melting clathrates boosting global temperatures for millennia (at least), would be a far greater disaster than most of us could imagine. It's as yet unclear what would make the difference between a mild abrupt ice age and an effectively permanent climate disaster; the likely tipping point issue is whether the ocean temperatures get hotter fast enough to melt the clathrates before the cooling effects of the mini ice age can really kick in. That is to say, this is another piece of evidence making it clear that we need to stop making things worse.


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Comments (18)


Well, we're either right about climate change, or the Climate Change Deniers are right. If we don't curb our C02 output, and nothing really bad happens, they were right.

Now, what are the odds....

Well, no. It's well-established that human-induced climate change is happening; the question is whether the overall results will be bad or awful (even if some groups or some locations aren't hit as hard as others). This is just another manifestation of the "bad" or "awful" dilemma.


Change, the enevitable frontier. It may loom or guide. Greenland is emerging from an age of frozen embrybionic evolution. What secrets lie beneath its icy mantle? What new plants will emerge when spring again warms her long forgotten summer's seeds? Must we fear every aspect of change? We are surely in for a future wrought with unknowns, don't make it a windfall for the long term investors in plutonium. Keep your minds open and don't be too easily swayed by powers you do not see.

Unfortunately, Louis, most of the suspected consequences of climate change are extremely negative from a human point of view in the Northern Hemisphere and potentially catastrophic in Africa. The potential upsides (longer growing seasons, a "greening" Greenland) are far outweighed by growing weather violence (e.g. New Orleans), rising sea levels, unpredictable agricultural shifts (and famines), the spread of pests and diseases, human conflicts over resources (especially water), and so on.

I think you'd be hard-pressed to say the we here at Worldchanging fear change, much less every aspect of change -- but some changes are simply and clearly for the worse.

Patrick Di Justo:

Remember also that there might not ever be a "correction" to the disrupted ocean circulation -- like any chaotic system, it might settle into a totally new state and remain fixed there until the next climate shift kicks it into yet another steady state.

Brad Arnold:

There is another catastrophic consequence of increased environmental CO2 levels-the acidification of the oceans.

The oceans are now becoming more acidic due to the simple chemical reaction: water combined with carbon dioxide produces carbonic acid. As the oceans inevitably become more saturated with carbon dioxide, they will become even more acidic, killing most of the aquatic life.

Since the beginning of the Industrial Revolution the oceans have absorbed an estimated half of the 800 billion tons of carbon dioxide emitted, but acidification of the oceans will cripple the "lungs of the planet."

If we can't reasonably stop our carbon dioxide discharges or prepare for the consequences of global warming, I suggest we engage in environmental engineering to remove the excess carbon dioxide.

There are many forms of life on earth that naturally perform this task, but we are overwhelming their ability to cope.

I submit that the only reasonable course of action is to improve by about ten times the ability of nature to remove excess carbon dioxide from the atmosphere and oceans. Biotechnology must be used to design genetically modified organisms that we will seed into the environment.

Dawn Watson:

Isn't Bush planning to pump CO2 into the oceans?

It sounds to me that given the inevitability of experiencing either a short lived Ice Age, or prolonged kill-all-the-humans (except the wooly ones) Ice Age, that the closing remarks are perhaps 180 degrees off. Rather than admit that "...this is another piece of evidence making it clear that we need to stop making things worse," it seems to me that we need to make things worser faster! I'm on my way out right now to buy myself a gas guzzling SUV and a cow.

A common mistake.

Here's the basic logic:

* Increased greenhouse gas warms the arctic, which melts freshwater ice.
* Freshwater runoff into the salt water cycle cuts it off, reducing the warm water to the north atlantic.
* This reduces the temperatures in northern Europe and possibly north America.

Putting *more* greenhouse gas into the air makes this process happen faster and hit harder, and would make it impossible to avoid. That is, it won't make the mini-ice age warmer, it would make it worse.

It *may* be that we'd need to do some warming if an abrupt ice age took hold, but trying to do that now is exactly the wrong strategy.

I appreciate your quick response, and your ability to glean from a rather tongue-in-cheeky post an actual question that readers will now be able to benefit from through what seems to be some rather solid insight. I love coming to your site for the articles and the posts, and your responses to the posts, etc. In fact, I set up a Google Alert for "WorldChanging" so I get regular emails of articles (I don't understand that whole RSS thing yet). I just don't know what I'm going to do with this cow now - who knew they were non-refundable?!


Jamais thanks for writing this: further proof that we not only need to stop doing the bad but that we really have to move beyond band aids and get into adaptation to a new climate regime... just one interesting tidbit, this quote comes from a BBC program two years ago called The Big Chill:

NARRATOR: This fifty gigotonnes of water melting from Greenland was the first evidence that global warming might be effecting the ice sheet here. But one change really shocked them. They started to measure one of the island’s biggest glaciers.

BOB THOMAS: Less than ten years ago, five years ago,it was moving at about six, seven kilometres per year.And that was more or less in balance with thesnowfall. Now in the five years since then the speedis almost doubled.

NARRATOR: It’s now advancing at twelve kilometres a year. The increase seems to be linked to global warming. It’s the fastest moving glacier on the planet

add this to the fact that the thermohaline conveyor is down by 30% (some downwelling sites are down to 25% of what they were a decade ago), notto mention all the paleochronological and geochronoligical proxy datat; and you have a plausible scenario that this is happening. in our lifetimes. I don't mean to sound like an alarmist, and we do have the technologies to still make food, electrify, all that we need, so it's really a matter of: how can we adapt, and on a timescale unseen in any spcies' history?


...also --as that planet's gone into 20 (not little) ice ages over the past 2 million years-- knowing what the ice does to the biosphere (remineralizing), will help us if we do chose to go towards the geo-engineering of climate...

(in a funny way, one big difference between now adn previous interglacial times, is that the forests were not cut down and sequesterd as boats, books, landfill newspapers, and architectures-- so the irony is that we're pumping CO2 into the air, from cars and coals, and in previous ends of interglacials (when CO2 also rose up) forest fires would go unabated. So while we think we're fancy monkeys, we're still operatives of Gaia. If she wants an ice age to cleanse and renourish the soils...


The difference in pumping co2 directly into the deep ocean is the pressure and temp turn it into dry ice that sinks and wont melt until the temp way down there goes up a fair bit.

Thats how the methane ice formations formed methane bubbling up and freezing under pressure.


The interesting group to watch are the insurance companies. They don't care about the politics or political correctness. They simply want to make money. They make their money be more accurately predicting the probability of events. Their models are already showing increased likelihood of extreme weather events.

Michael Anders:

I am mystified at how this climate change process will play out in the Pacific and the western U.S. There is much discussion about the Gulf Stream circulation and how that potion of the world might be affected by global warming, but little discussion about ocean circulation elsewhere on the globe and how climate chage might affect or be affected by changes in these ocean currents? I wonder if anyone has information regarding this... I would love to hear it. I also wonder how volcanic activity, earthquakes, solar activity, etc... plays into this process of global warming and glaciation. Thanks for your comments.


Avery you wanna have fun check out the ReInsurers. While the insurance industry starts to rally (mostly in ways to cover their hides) the guys who haveto pay them out, like municRE or SwissRE-- those are the ones stepping up to the plate at cop11 and other global scaled get togethers...


In a nutshell back 500 some years ago california had snow at sea level in los angeles every year and the rainfall was VERY much more then it is today.

Then a cooler and dryer and milder climate took over.. that weather cycle lasted 500 some odd years and was going to change anyway around this time... in fact acient calaendars are thought to be based on this long climate cycle.

Well global warming likely will make things even more intense and eventful then expected.

If you live in an extinct lake bottom as many do... its time to ponder moving.


The findings you use all seem to forget two items in the picture, mass methane gas releasment, and multi volcanic eruptions.
Cross check your eruption data with the increse of projected forcasts.


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