Posted by: JohnnyRook | August 21, 2008

The Earth’s Climate Can Flip In a Single Year New Research Shows

The idea of abrupt climate change is only slowly making its way into the popular mind. Although scientists have been aware for over two decades that climate can lurch quickly from one state to another, geological speaking, the average person still has difficulty in imagining climate changing in anything less than millions or thousands of years or perhaps, at best, centuries. This is undoubtedly one of the reasons that many people still fail to feel any sense of urgency about Climaticide.

Abrupt climate change has been discussed by such science writers as John D. Cox in Climate Crash: Abrupt Climate Change and What It Means for Our Future and Fred Pearce in With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change. Cox describes the discovery of abrupt climate change while Pearce writes of possible abrupt future climate change as a result of global warming.

However, new research now indicates that climate may change even faster than anyone imagined.

It is generally accepted that that the last glacial period began about 110,000 years ago and ended around 15,000 BP.

According to Wikipedia:

The last glacial period is sometimes colloquially referred to as the “last ice age”, though this use is incorrect because an ice age is a longer period of cold temperature in which ice sheets cover large parts of the Earth. Glacials, on the other hand, refer to colder phases within an ice age that separate interglacials. Thus, the end of the last glacial period is not the end of the last ice age. The end of the last glacial period was about 12,500 years ago, while the end of the last ice age may not yet have come: little evidence points to a stop of the glacial-interglacial cycle of the last million years.

The maximum extent of glaciation during the last glacial period occurred around 18,000 years ago. After that the earth began to warm and the great ice sheets to retreat. Temperatures eventually reached levels similar to those we experience today. Then, suddenly, around 13,000 years ago temperatures dropped and ice sheets resumed their expansion. This period, known as the Younger Dryas, after an alpine/tundra flower common at the time, lasted for approximately 1,000 years.

Dryas octopetala

There is disagreement about what caused the Younger Dryas period. The traditional interpretation is that it was caused by a shutdown or weakening of something called the thermohaline circulation or ocean conveyor. This phenomenon is also sometimes called, incorrectly, the meridional overturning circulation (MOC). For our purposes here, the differences between the two concepts are irrelevant.

In very simplistic terms what supposedly happens is this: surface currents from the tropics carry warm water north to Northern Europe where the water is cooled by northern winds, which also cause evaporation and make the water saltier (i.e. denser). This colder, saltier water then sinks into the deep ocean and returns southward. A more detailed description is available at the Wikipedia link immediately above. An important byproduct of the thermohaline circulation is that the U.K. and Northern Europe enjoy warmer temperatures than they would otherwise. (Compare the temperatures at similar latitudes in North America.)

Thermohaline Circulation

This interpretation, however, is not universally accepted. Wikipedia summarizes the state of the dispute as follows:

The thermohaline circulation plays an important role in supplying heat to the polar regions, and thus in regulating the amount of sea ice in these regions. Changes in the thermohaline circulation are thought to have significant impacts on the earth’s radiation budget. Insofar as the thermohaline circulation governs the rate at which deep waters are exposed to the surface, it may also play an important role in determining the concentration of carbon dioxide in the atmosphere. While it is often stated that the thermohaline circulation is the primary reason that Western Europe is so temperate, it has been suggested that this is largely incorrect, and that Europe is warm mostly because it lies downwind of an ocean basin, and because of the effect of atmospheric waves bringing warm air north from the subtropics.[3] However, the underlying assumptions of this particular analysis are not generally supported,[4] and much research supports the role of the THC in transporting heat to Europe.[5]

Large influxes of low density meltwater from Lake Agassiz and deglaciation in North America is thought to have led to a disruption of deep water formation and subsidence in the extreme North Atlantic and caused the climate period in Europe known as the Younger Dryas.[6]

Recent research by a team lead by Achim Brauer of the German Reseach Institute Centre for Geosciences and published on August 1, 2008 in Nature Geoscience (subs. required) with the title, An abrupt wind shift in western Europe at the onset of the Younger Dryas cold period, advances a different theory.

Lake Meerfelder Maar

Brauer’s team analyzed the varves from Lake Meerfelder Maar in western Germany. The varves in the lake, which is situated deep within a volcanic crater, contain a continuous temporal record that extends through the Younger Dryas. Brauer believes, based on geochemical and other analyses of the varves that changes in sea ice extension chilled the Northerly winds, which in turn affected the temperature of ocean currents and produced the dramatic temperature drop and growth of glaciers that marked the Younger Dryas.

It is well beyond my expertise to evaluate the merits of the competing theories, and I shall not attempt to do so. What I do want to highlight however is the degree of precision that Brauer’s team was able to obtain in dating the onset of the Younger Dryas.

According to Brauer’s paper:

With the onset of the Younger Dryas cold period, the formation of thick monospecific diatom layers (Stephanodiscus sp.) during spring/summer is explained by an increase in the wind-driven upward mixing of nutrient-rich bottom water. The reworked sediments argue for a major fall in lake level and an increase in wave activity at the shoreline due to windy conditions. Particularly striking are the pronounced inter-annual to decadal oscillations before the final shift, which occurred within one year. These short term fluctuations indicate that the change from calm and wet to windy and dry conditions began with a period of individual extreme years with Younger-Dryas like-conditions. However the depositional system in the lake switched back after these extreme years to Allerød-like conditions until the permanent shift at 12,679 varve year BP [emphasis-JR]

.

In other words, after some years of erratic weather a tipping point was passed and in a single year norther Europe went from temperatures similar to those we now experience to glacial conditions. Temperatures at the summit of Greenland plummeted to 15C less than today.

Dr. Brauer’s research is worth remembering the next time that you are talking with a climate denialist/delayer who is arguing that we need to do more research before we decide what to do about Climaticide. We now know that the earth’s climate is capable of making dramatic long-lasting jumps within extremely short time frames. It has already happened.

We could get lucky… Maybe it won’t happen again…

But wouldn’t it be wiser to take action now to cut our emissions and eventually rollback levels of greenhouse gases which we know are heating up the planet and destabilizing the climate? Or do we want to cross our fingers, continue to point the gun at our head and and hope each time we pull the trigger (which is what we do every year that we postpone dealing with Climaticide) that the chamber beneath the firing pin is one of the empty ones?

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Responses

  1. Those preplunge oscillations are very interesting. They are not uncommon in nonlinear systems with thresholds; just turn down the gain on the feedback loop of something that pops and you can see them.

    The current opinion on YD-like plunges is that, lacking a lot of North Atlantic sea ice, the thermohaline sinking isn’t sudden but gradual–but that still means a time scale of a century to lose it, pretty rapid. The rearrangment of the winds and rains, just from the altered distribution of sea surface temperatures, is what would get civilization into big trouble, not mean temp shifts. Along about chapter 15 of my new book (Global Fever: How to Treat Climate Change), I go into this.

  2. Thanks, Dr. Calvin. I’ve ordered your book and look forward to reading it.

    Do you have a take on this question? Dr. Brauer rejects the idea that the YD was caused by the melting of ice shields shutting down the Meridional Overturning Circulation (no evidence of melt flow that matches up chronologically according to him) in favor of a theory based on sea-ice growth leading to colder northerly winds.

    But, doesn’t this beg the question? If sea-ice growth affected wind temperature, which, in turn affected land surface temperature, something had to have caused the sea-ice growth. Do you have any idea what that might have been?


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