New on the Web: Mark Steyn gives his hilarious take on the Dec 2005 confab of COP-11 in Montreal. Chris Horner of the Competitive Enterprise Institute, reports from Montreal: "… Kyoto is increasingly obviously designed to fail (the particular charade of such dysfunction requiring another essay entirely). Greens and their cheerleaders might find a more appropriate announcement in Chevy Chase's classic Saturday Night Live offering: 'This just in. Generalissimo Francisco Franco is still valiantly holding on in his fight to remain dead.'" Philip Stott sees a pattern of manic depression in COP meetings (Item #1).
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Kyoto is crumbling in Europe, according to the Yorkshire Post (Item #2) and the BBC (Item #3). And now the Northeast states' mini-Kyoto initiative may collapse, as Mass. governor Mitt Romney pulls out of the accord because of huge costs for consumers. Big distress at the NY Times (Item #4), which still believes in the Tooth Fairy and that emission trading can eliminate costs. [There is a bridge in Brooklyn I'd like to sell them.] Meanwhile, the NY Times (Dec. 28) also reports In Russia, Pollution Is Good for Business "Some Eastern European companies are poised to earn hundreds of millions of dollars through trading their rights to release carbon dioxide into the air." Evidently, Europe is not only paying high prices for Russian gas but also footing the bill for upgrading their outdated and polluting coal-fired electric plants, thereby earning pieces of paper called emission credits. And all this for a worthless but costly Kyoto Protocol.

In Russia, Putin's economic adviser has been an outspoken opponent of Kyoto. Now Andrei Illarionov may have become too outspoken; he has just resigned (Item #5). There was no suggestion of this earlier this month, when we both addressed a prestigious international group, meeting in Washington DC under the chairmanship of Lord Lamont (former Chancellor of the Exchequer under Margaret Thatcher). I had suggested to Andrei he should advise Putin to pardon Khodorkovsky and appoint him as Russia's energy minister. Andrei agreed and gave a wry smile.

On the Kyoto front: We learn from a research paper in Science that tree farms designed to soak up CO2 would also soak up gobs of water and cause big environmental problems (Item #6). You can't win in this sequestration game, it seems. Another example of the CO2 mania: Shell Oil is accused of violating Nigerian law by flaring natural gas, but is appealing (Item #7). The action was instigated by environmental groups who are not impressed with Shell's campaign to project a Green image. In our view: It couldn't happen to a nicer company.

For some common sense in environmental matters, it's best to turn to Michael Crichton and his latest public address (with great graphics too):
"Fear, Complexity, & Environmental Management in the 21st Century"
http://www.michaelcrichton.com/speeches/complexity/complexity.html
It's the best antidote to the Club of Rome -- that overpopulation (a la Paul Ehrlich) would do us in, resources would run out, and pollution would kill us all before the end of the century.

[On a personal note: I actually believed some of these myths around 1967, when I gave up pure science for a while to become a Deputy Asst Secretary of Interior in charge of fighting water pollution, preserving the estuaries, desalting sea water, and all sorts of other good things. But I had some nagging doubts. So in 1969 I organized a 3-day Symposium on "Is There an Optimum Level of Population." My eyes were opened after listening to Alvin Weinberg (Oak Ridge), Chauncey Starr (EPRI), Joseph Fisher (of RFF), and others. The result was an edited book, published by McGraw-Hill, and a drastic change in my career from pure atmospheric and space science to public policy issues. In the process I had to teach myself some economics, of course.
So when the Club of Rome's Limits to Growth appeared in 1972, I was ready to take them on-along with John Maddox and Julian Simon. (More recently, I read a fine critique by Yale economist Bill Nordhaus.) But Ehrlich and his disciples are now mainly in the Global-Warming disaster mode and have postponed the other catastrophes.]
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And finally, for a bit of important science that's not gotten much notice:
Mechanisms for climate variability during glacial and interglacial periods
Sea Ice may be the Cause of Climate Instabilities

Loving, Jolene L., and Geoffrey K. Vallis, 2005. Mechanisms for climate variability during glacial and interglacial periods. Paleoceanography, 20, PA4024, doi:10.1029/2004PA001113, December 17, 2005

The authors are able to reproduce many aspects of observed glacial climate variability (e.g., Dansgaard-Oeschger oscillations) without external forcing and provide a natural explanation for the prevalence of high-amplitude variability in glacial climates and the relative stability of the warm Holocene. (For excerpts see Item #8)

This work is of extreme interest to us, because Dennis Avery and I are preparing a major survey article on the 1500-yr climate oscillation. Two points stand out from the Loving-Vallis paper:

1. The oscillation is strongest during glaciations. The climate is more stable in the Holocene, i.e. during warm periods --as I have argued repeatedly.

2. But L-V have proposed and tested an actual mechanism, namely ice cover. I.e., the current reduction in ice cover will INCREASE climate stability. At least, this is the conclusion I would draw from their work.
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1. Manic-depression and 'global warming' hype.....
http://greenspin.blogspot.com/
by Philip Stott, December 14, 2005

I have already commented on the manic-depressive tendencies presented by participants and camp followers at major 'global-warming' meetings, such as those held in The Hague (2000), in Marrakech, Morocco (2001), in Edinburgh around the G8 Summit (2005), and in Montreal (this month).

The 'meeting' is first reported to be 'failing drastically', with participants walking out or raising 'impossible' issues. The 'meeting' then extends into the early hours of the morning after the day on which it is meant to have closed, the host nation using every trick in the moral-blackmail book to achieve 'something' for home consumption. A bland agreement is cobbled together at the very last minute. Thousands of participants and journalists emerge from their fierce-small-world 'euphoric', tears are shed, and the 'success' of the meeting is overhyped and over-spun - "the world can breathe again". Then, inevitably, in the cold light of day, the euphoria turns quickly to angst and to bitterness as it becomes increasingly obvious that little to anything has been achieved. The high is followed by a long depression.

If you examine carefully the symptoms exhibited following these repeated 'meeting patterns', while analysing in detail the changing media language involved, it becomes obvious that 'global warming' hype is leading to clinically-identifiable symptoms closely associated with those presented in 'mass psychogenic illness', or 'mass sociogenic illness'.
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2. Europe's Kyoto Policy Crumbles

The Yorkshire Post, 26 December 2005 http://www.yorkshiretoday.co.uk/ViewArticle2.aspx?SectionID=104&ArticleID=1296096

AFTER repeatedly posing as global exemplars in the fight against global warming, the European Union's member-states need to take a long, hard look at the cold figures.

According to a new study, 10 of the EU's 15 signatories to the Kyoto agreement are on course to miss their target to reduce greenhouse gases by five per cent of their 1990 figure by 2008-2012. Indeed, the Institute of Public Policy Research says that Britain is almost alone in Europe in making progress towards fulfilling its Kyoto commitments.

Indeed, looking at the wider world, Britain's performance - achieved largely through the contraction of the coal industry - stands out even more. Canada, for example, which played host to a major international climate-change conference in Montreal earlier this month, says it remains fully committed to its Kyoto obligations. However, by the end of 2003, its emissions were up 24.2 per cent on 1990 levels.

Meanwhile, since 2001, a period in which greenhouse-gas emissions across the EU have increased, those from the United States have fallen by almost one per cent. America may still be one of the world's worst polluters, but it is increasingly clear that those who seek to demonise Washington as the saboteur of Kyoto are hardly leading by example. Yet there has been as much hot air emitted by these countries' politicians, in their exhortations to the world to take action, as by their pollution-belching industries.

Kyoto was never meant to be an excuse for the self-righteous among nations to preen themselves on the global stage while doing nothing concrete to meet their own grandiose pledges. Yet, as the date nears by which action is supposed to have been taken, it is increasingly clear that this is the case.

If Europe and Canada cannot back up their fine words with deeds, how can they ever hope to persuade the US of the worthiness of Kyoto? More to the point, how can they have any impact on China and the rapidly industrialising nations of Asia, whose projected emissions levels are likely to make the sacrifices made by countries such as Britain completely irrelevant?
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3. Europe 'behind on Kyoto pledges
from BBC NEWS: http://news.bbc.co.uk/go/pr/fr/-/1/hi/uk_politics/4561576.stm
Dec. 26, 2005

The UK is almost alone in Europe in honouring Kyoto pledges to cut greenhouse gases, a think-tank claims.

Ten of 15 European Union signatories will miss the targets without urgent action, the Institute for Public Policy Research (IPPR) found. The countries include Ireland, Italy and Spain. France, Greece and Germany are given an "amber warning" and will not reach targets unless they put planned policies into action, the IPPR said.

Only Sweden and the UK were on course to meet their commitments, the think-tank's study found. IPPR associate director Tony Grayling commented: "We are nearing the point of no return on climate change. "We have very little time left to start reducing global greenhouse gas emissions before irreparable damage is done. "It is vital that EU countries keep their promises to cut pollution," he said.

European countries needed to take action, including energy saving and investing in renewable energy. "In the new year, EU countries will need to adopt tougher limits on emissions from power stations and heavy industry, in the second phase of the EU Emissions Trading Scheme," Mr Grayling said. Under Kyoto commitments, the European signatories are supposed to cut their emissions to 8% below 1990 levels by 2008-2012.

The Kyoto commitments have been undermined, critics say, because the US - the world's biggest emitter of greenhouse gases - has refused to ratify the treaty. An EU body - the European Environment Agency - warned in November that the EU was likely to cut its emissions by only 2.5% by the year 2012 - rather than the 8% the bloc promised.
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4. Governor Romney Bails Out

NY Times Editorial, December 28, 2005

Seven Northeastern states, including New York, New Jersey and Connecticut, have embarked on a region-wide plan to reduce power plant emissions of carbon dioxide, which contributes to global warming. Two years in the making, the plan is the first collective effort in America to adopt mandatory controls for greenhouse gases. It is further evidence of the states' willingness to address an issue that Washington has largely ignored, as well as a timely antidote for the administration's dispiriting performance at the recent global warming conference in Montreal.

The governors' message would have been stronger still had it not been for the defection of Gov. Mitt Romney, the Massachusetts Republican. He pulled the rug out from under his own negotiators with an 11th-hour complaint that the plan would impose unacceptable utility costs on consumers.

His case is unconvincing. The program's target - a 10 percent reduction in current emissions levels by 2019 - is modest indeed. Its design includes a market-based trading scheme aimed at reducing emissions cheaply, much as the successful federal acid rain program enacted in 1990 did. Last-minute changes, aimed largely at calming Mr. Romney's nerves, provided additional safety valves in case electricity prices rose to uncomfortable levels.

Still Mr. Romney balked, leaving the impression that he was simply pandering to the White House and his party's right wing to further his presidential ambitions. The governor insists otherwise but, like it or not, he now finds himself the darling of Washington's ultraconservative think tanks, which have no use for greenhouse gas controls, and of James Inhofe, the reactionary chairman of the Senate Environment and Public Works Committee, who regards global warming as a "hoax."

Meanwhile, Mr. Romney's gubernatorial compatriots - including New York's governor, George Pataki, himself a potential presidential aspirant - look bolder by comparison. The new multistate plan is no substitute for a national program of emissions controls, but the very fact that it exists should encourage those in Congress who seek one.
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5. Illarionov Resigns as Putin Adviser
By Dr Alister McFarquhar in: Environment o
http://www.adamsmith.org/blog/

Reuters reports the resignation of Andrei Illarionov, who, until last January, headed Russia's team at the G8 group of industrialized nations. This helps explain the denouement of the Kyoto Treaty, which I rate among the greatest global scams in history. Russia first rejected Kyoto on the advice of its scientists, but subsequently joined after pressure from Britain no doubt involving appropriate sweeteners.

"..it is one of the paradoxes of the Kyoto Protocol on climate change that companies in Russia and other Eastern European countries, which are among the world's largest producers of greenhouse gases, are poised to earn hundreds of millions of dollars through trading their rights to release carbon dioxide into the air. The potential value for Russia ranges from $20 billion to $60 billion." [Andrew E. Kramer, The New York Times, 28 December 2005]

Illarionov has compared Kyoto to an "economic Auschwitz". He says "The Kyoto protocol is destructive for science and the environment, for public health and safety, for economic growth, and for the international fight against hunger and poverty.... Like fascism and communism, Kyotoism is an attack on basic human freedoms behind a smokescreen of propaganda. Like those ideologies of human hatred, it will be exposed and defeated." [Financial Times, 15 November 2004]

Benny Peiser on CCNet explains how "The international scientific community was plunged into disarray as news emerged yesterday how Britain's Royal Society has been orchestrating a political campaign behind the back of the Russian Academy of Science. In a calculated attempt to overthrow the well-known skeptical position of the Russian Academy of Science on climate change, the Royal Society appears to have pressured its president, Yuri Osipov, into signing a politically motivated document against the expressed stance of its own organization.

The activities of Lord May, President of the Royal Society, appear to have backfired: "Instead of providing evidence of an international 'scientific consensus' on climate change, the public retraction by the Russian Academy of Science from the Royal Society's unduly political G8 statement has exposed the whole exercise as a complete farce. As a result, the reputation and integrity of the world's leading scientific academies have been severely damaged."

My skepticism on Kyoto has been recorded here many times. When realpolitik dominates science we are truly in trouble. Can scientists any longer be trusted? And what have we learned? Post Kyoto the EU and UK energy policy continues to assume incorrectly that carbon emissions account for a significant proportion of current warming and that the contribution by man is large enough to be relevant. Actually there is a better case for conserving energy based on likely supply difficulty and cost, rather than on carbon pollution.
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6. Carbon sequestration with tree farms causes water problems
Research paper in Science

Tree plantations are a potentially valuable tool for slowing the increase of carbon dioxide concentrations in the atmosphere, but they also can affect the water and soil resources on which they depend. Jackson et al. (p. 1944) analyze these often-neglected effects, using a combination of field research, regional economic and climate modeling, and more than 600 already-published observations, to show that afforestation can dramatically reduce water availability, as well as salinize and acidify the surrounding soil. They find that tree plantations caused nearby streams to dry up in more than one-tenth of the cases studied, and that stream flow was reduced by half, on average. These findings should help illuminate the costs of carbon sequestration by afforestation, rather than only their benefits.
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5. Contempt Case for Shell over Gas
By Richard Black, Environment Correspondent, BBC News website

The oil multinational Shell is facing contempt-of-court proceedings in Nigeria over gas flaring. Last month, a court ordered the company to stop flaring gas from oil wells in the country, which accounts for much of Africa's greenhouse gas emissions. Shell has not halted the practice, so campaign groups have initiated proceedings for contempt of court, which can result in imprisonment. Shell has appealed against the initial judgement and denies it is in contempt.

In November, the Nigerian Federal Court, sitting in Benin City, ruled on a case brought by environmental and social groups on behalf of the Iwherekan community of Delta State. They argued that flaring creates significant local pollution and health problems, and is inherently wasteful of a resource which could bring income to local communities. International environmental groups also argue it is a significant source of greenhouse gas emissions, with flaring in Nigeria perhaps the biggest source of emissions in Africa.

The Benin court ruled that gas flaring amounts to "...a gross violation of [the plaintiffs'] fundamental right to human life and dignity...", and that Shell and the Nigerian National Petroleum Corporation had broken national law by failing to carry out an environmental impact assessment. By failing to stop flaring, as ordered by the court, campaigners now argue Shell is in contempt, and have initiated proceedings in the Federal Court.

"Since judgement was passed, Shell has not halted her illegal activities," said Nnimmo Bassey, of the Nigerian group Environmental Rights Action. The company has made a further appeal because it believes that the court did not adopt the correct procedure.

"We see a multinational corporation that has no respect for the rule of law, but who at every turn loves to characterise local people as vandals and saboteurs." Earlier this month, an attack with explosives on an oil pipeline forced Shell to suspend extraction at two of its wells and delay shipments. The background to this and other incidents is the view held by some Nigerian communities that they do not benefit from oil wealth, with profit going to the multinationals.

"It's astonishing that Shell has not complied with this court order preventing it from continuing gross violations of human rights," added Peter Roderick of the international organisation Climate Justice, which has been involved with the action. "Its behaviour seriously undermines respect for the rule of law that its operations rely on."

The company says it flares the gas rather than processing it because there is no local market and no facilities which could liquefy it for export, though such facilities are now under development. Shell and the Nigerian government have both committed to phase out flaring in Nigeria by 2008. In 2004 the World Bank said that companies operating in Nigeria, which include Shell, ExxonMobil and Chevron, flare 75% of the gas that they produce.

Story from BBC NEWS: http://news.bbc.co.uk/go/pr/fr/-/1/hi/sci/tech/4556662.stm
Published: 2005/12/24 16:16:06 GMT
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8. Mechanisms For Climate Variability During Glacial And Interglacial Periods
Sea Ice may be the Cause of Climate Instabilities

Loving, Jolene L., and Geoffrey K. Vallis, 2005. Mechanisms for climate variability during glacial and interglacial periods. Paleoceanography, 20, PA4024, doi:10.1029/2004PA001113, December 17, 2005

The authors are able to reproduce many aspects of observed glacial climate variability (e.g., Dansgaard-Oeschger oscillations) without external forcing and provide a natural explanation for the prevalence of high-amplitude variability in glacial climates and the relative stability of the warm Holocene.

(Excerpts courtesy of Timo Hameranta)

"Several aspects of the geological record from the last glacial period have continued to lack adequate explanation. In particular, the high-amplitude variability in temperature on millennial timescales (Dansgaard-Oeschger cycles), as well as abrupt transitions between North Atlantic thermohaline circulation states remain perplexing [Dansgaard et al., 1984, 1993; Sarnthein et al., 1995; Clark et al., 2002; Pflaumann et al., 2003]. In this paper, we show how these and other features of glacial climates may arise naturally from the prevailing cold conditions.

The geologic evidence for Dansgaard-Oeschger events is widespread over much of the Northern Hemisphere so the mechanisms involved must influence climate on a correspondingly large scale [Keigwin et al., 1994; Broecker and Hemming, 2001; Voelker, 2002]. Since oceanic heat transport by the thermohaline circulation has potential for global impact, its variability would provide an explanation for glacial warm cycles [Keigwin et al., 1994; Ganachaud and Wunsch, 2000; Broecker and Hemming, 2001]. However, although the variability and possible multiple equilibrium states of the thermohaline circulation have long been thought relevant to this issue [Stommel, 1961; Manabe and Stouffer, 1988], a robust mechanism for producing self-sustained oscillations, which are of a large magnitude only in a glacial climate, and require no external triggering, has remained elusive. Furthermore, the increased overall pole-to-equator atmosphere temperature gradient of glacial climates might suggest a more vigorous and perhaps more stable thermohaline circulation, whereas the opposite appears to have been the case [CLIMAP Project Members, 1976; Broecker, 1996; Ruhlemann et al., 1999]. Nevertheless, proxies for low temperatures, and for reductions in North Atlantic Deep Water production, coincide in ocean sediments, suggesting that weaker North Atlantic Deep Water formation was associated with high-latitude cooling during glacial periods [Boyle and Keigwin, 1985; Keigwin and Jones, 1994; Keigwin and Lehman, 1994; Rutberg et al., 2000]. This evidence supports the hypothesis that climate variability during the last glacial period is linked to reductions in northern heat transport by the thermohaline circulation.

Most attempts to explain glacial cooling and variability have focused on steady or periodic high-latitude freshening of the North Atlantic [Stocker and Wright, 1991; Weaver et al., 1991; Manabe and Stouffer, 1995, 1997; Sakai and Peltier, 1997, 1999; Ganopolski and Rahmstorf, 2001; Clark et al., 2002; Rahmstorf, 2002]. Typically, applied freshwater forcing induces switching between states of thermohaline circulation and one explanation for glacial climate variability is periodic switches between circulation states [Alley et al., 2001; Rahmstorf, 2003]. Here we show that cold conditions alone are sufficient to produce weakness in the thermohaline circulation, switches between circulation states and climate variability which are physically similar to Dansgaard-Oeschger cycles. With this cold climate mechanism, no external freshwater forcing is required to explain the observed variability in the North Atlantic region during the last glacial period.

Although geologic evidence supports a link between climate variability during the last glacial period and reductions in northern heat transport by the thermohaline circulation, a direct connection between high-latitude freshening and thermohaline circulation variability is not always apparent. For example, there is an increase in the strength of the thermohaline circulation and rapid warming following large surface fluxes of fresh water during Heinrich events [Heinrich, 1988; MacAyeal, 1993]. So a mechanism, such as the one we present, for climate variability during cold periods which does not require external freshwater forcing is consistent with the geologic record for the North Atlantic region during the last glacial period.

In order to separate the effects of cooling the climate system from the effects of high-latitude freshening we conduct two sets of experiments: First, we cool the atmosphere without changing the salinity forcing to simulate glacial cooling (cooling without freshening). Second, we increase high-latitude freshening without changing the surface temperature (warm climate with freshening).

Both of our experiment sets start with the same warm climate experiment (control experiment) that exhibits thermohaline circulation characteristics which are similar to the current North Atlantic thermohaline circulation. In our analysis we include a detailed comparison between our model results and the geologic record for the last glacial period.

Conclusion and Discussion

In this paper we have explored mechanisms for glacial climate variability using a three-dimensional ocean model coupled to an energy balance atmosphere, and using a simpler ocean box model. We find that cooling alone, with no additional forms of external forcing or variability, leads to a climate with two of the most significant features of the observed glacial climate:

1. The glacial climate is less stable and is characterized by intermittent, millennial-scale oscillations similar in many ways to Dansgaard-Oeschger cycles.

2. The glacial ocean circulation is generally weaker with shallower Northern Hemisphere overturning, and the deep water formation region is shifted equatorward of the present sinking region.

Both of these features are a consequence of the growth of sea ice. Sea ice inhibits the loss of buoyancy at high latitudes and leads to a generally weaker and shallower overturning circulation with midlatitude (rather than high latitude) sinking near the edge of the ice sheet. (This is consistent with Boyle and Keigwins [1987] finding that North Atlantic Deep Water production was replaced by increased southern sinking intermediate water during cold periods.) This circulation is unstable, and millennial-scale oscillations are produced. During these events, the overturning circulation is much stronger and high latitudes are considerably warmer than normal for glacial periods.

Sea ice also plays a role in the sawtooth-shaped atmospheric temperature profile which is apparent during overturning oscillations (Figure 6): Melting sea ice enhances rapid warming at the beginning of a cycle, and the meridional overturning circulation is able to quickly spin up and warm high latitudes. The subsequent cooling is more gradual, but the increase in albedo and the insulating effect of sea ice cause rapid cooling at the end of a warming cycle. That sea ice is important is consistent with the models of Gildor and Tziperman [2000] and Kaspi et al. [2004], in which sea ice switches enhance the abrupt atmospheric temperature changes at northern latitudes, where sea ice is melting and freezing.

The simulated features of oscillations are generally consistent with observed Dansgaard-Oeschger cycles, and several aspects that both the model and observations have in common are (1) high-latitude sawtooth-shaped temperature profile, (2) warm events occurring approximately every 2500 years, (3) higher-amplitude warm events occurring approximately every 7000 years, (4) high-latitude sea surface temperature change of 2!C over a cycle, and (5) high-latitude atmosphere temperature change of the order of 15!C over a cycle.

Of course, some of these numbers are dependent upon parameters in the model. For instance, when the diffusivity parameter is reduced the oscillation period lengthens (because it then takes longer to warm the deep ocean to the point of instability), but the period remains between 1000 to 3000 years over a broad range of diffusivity values. Nevertheless, it is notable that the model can reproduce many of the features of the observed glacial climate without additional external forcing and without excessive tuning.

High-latitude freshening in a warm climate impacts the thermohaline circulation and climate very differently than overall cooling of the climate. In general, the high-latitude sinking in our warm climate integrations is very stable. From our three-dimensional results we estimate that, when the climate is warm, the freshwater forcing at the surface has to be quadrupled to cause a shift to weak reverse overturning. Furthermore, such freshening alone does not produce a shift to mid-latitude sinking or variability such as occurred during glacial periods.

We find that neither stochastic forcing (emulating weather) nor a seasonal cycle is necessary to produce variability in our experiments, but neither does their presence damp such variability. In particular, the millennial-scale variability is also present in experiments which include a seasonal cycle.

Millennial variability is also present in experiments without stochastic forcing. Figure 13 shows a time series for temperature in the e = 0.73 experiment without stochastic forcing. Without stochastic forcing the warming events are more regular in period and amplitude. Stochastic forcing increases the amplitude variation for warming events, causing the higher-amplitude warming events approximately every 7000 years and increases the variability of the model climate between major cycles, but has only a small effect on shape or period of the large-magnitude cycles.

Finally, let us mention a main limitation of this work, namely the use of a single-hemisphere ocean basin. This cannot correctly represent the geography of the North Atlantic Ocean and so features such as exact latitude or depth of a particular event cannot be credibly compared to the geologic record. This of itself is of little consequence, but perhaps more seriously, inter-hemispheric phenomena cannot be modeled, and so one might argue the model is seriously deficient. However, we may invert such reasoning, and argue that the ability of the simple model to produce reasonably realistic circulation has allowed the essential mechanism to be extracted more easily, and further suggests that inter-hemispheric variations, while certainly present in the historical record, are a consequence and not a cause of a mechanism that has its roots in the North Atlantic. A related issue is that in some theoretical and numerical models of the overturning circulation, an important role is played by the wind forcing in the Antarctic Circumpolar Current [Toggweiler and Samuels, 1998; Vallis, 2000]. However, in addition to that wind, the presence of a source of dense water in the North Atlantic is necessary to produce such a circulation, and sea ice cover in the North Atlantic will certainly affect this. In that case, of course, the value of the diffusivity would play a lesser role. Clearly, the next step is to use a more realistic model that allows inter-hemispheric and even inter-basin exchanges, for these are important aspects of the real climate system.

In summary, our results support the notion that the overturning circulation of the ocean plays a significant role in the variability of glacial climates. More specifically, we suggest that cooling and the growth of sea ice and the corresponding weakness and instability of the overturning circulation are responsible for this variability, and we have offered a mechanism whereby this may occur. The mechanism is sufficient to explain the presence and some of the properties of Dansgaard-Oeschger cycles during glacial cycles and the relative stability of the Holocene.