This article, first published by the Woods Hole Oceanographic Institution on February 10th, 2003, is about the Thermohaline Circulation System – though they do not explicitly use that phrase within the article.
This could be considered a CounterCurrents article because the general expectation is that Global Warming will make the world warmer everywhere but, in fact in some places, it might get considerably colder – which seems very counter-intuitive.
If you don’t know about the possibility that the North Atlantic region could get a lot cooler as a a result of Global Warming, then this is a great article for you.
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By Terrence Joyce, Senior Scientist, Physical Oceanography and Lloyd Keigwin, Senior Scientist, Geology & Geophysics
When most of us think about Ice Ages, we imagine a slow transition into a colder climate on long time scales. Indeed, studies of the past million years indicate a repeatable cycle of Earth’s climate going from warm periods (“interglacial”, as we are experiencing now) to glacial conditions.
The period of these shifts are related to changes in the tilt of Earth’s rotational axis (41,000 years), changes in the orientation of Earth’s elliptical orbit around the sun, called the “precession of the equinoxes” (23,000 years), and to changes in the shape (more round or less round) of the elliptical orbit (100,000 years). The theory that orbital shifts caused the waxing and waning of ice ages was first pointed out by James Croll in the 19th Century and developed more fully by Milutin Milankovitch in 1938.
Undefined Ice age conditions generally occur when all of the above conspire to create a minimum of summer sunlight on the arctic regions of the earth, although the Ice Age cycle is global in nature and occurs in phase in both hemispheres. It profoundly affects distribution of ice over lands and ocean, atmospheric temperatures and circulation, and ocean temperatures and circulation at the surface and at great depth.
Since the end of the present interglacial and the slow march to the next Ice Age may be several millennia away, why should we care? In fact, won’t the build-up of carbon dioxide (CO²) and other greenhouse gasses possibly ameliorate future changes?
Indeed, some groups advocate the benefits of global warming, including the Greening Earth Society and the Subtropical Russia Movement. Some in the latter group even advocate active intervention to accelerate the process, seeing this as an opportunity to turn much of cold, austere northern Russia into a subtropical paradise.
Evidence has mounted that global warming began in the last century and that humans may be in part responsible. Both the Intergovernmental Panel on Climate Change (IPCC) and the US National Academy of Sciences concur. Computer models are being used to predict climate change under different scenarios of greenhouse forcing and the Kyoto Protocol advocates active measures to reduce CO² emissions which contribute to warming.
Thinking is centered around slow changes to our climate and how they will affect humans and the habitability of our planet. Yet this thinking is flawed: It ignores the well-established fact that Earth’s climate has changed rapidly in the past and could change rapidly in the future. The issue centers around the paradox that global warming could instigate a new Little Ice Age in the northern hemisphere.
Evidence for abrupt climate change is readily apparent in ice cores taken from Greenland and Antarctica. One sees clear indications of long-term changes discussed above, with CO² and proxy temperature changes associated with the last ice age and its transition into our present interglacial period of warmth. But, in addition, there is a strong chaotic variation of properties with a quasi-period of around 1500 years. We say chaotic because these millennial shifts look like anything but regular oscillations. Rather, they look like rapid, decade-long transitions between cold and warm climates followed by long interludes in one of the two states.
The best known example of these events is the Younger Dryas cooling of about 12,000 years ago, named for arctic wildflower remains identified in northern European sediments. This event began and ended within a decade and for its 1000 year duration the North Atlantic region was about 5°C colder.
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