Paul MacRae, July 30, 2008

The determinants of complex processes are invariably plural and interrelated.

— David S. Landes, The Wealth and Poverty of Nations, p. 517

Most of what “consensus” climate science tells the public about human-caused global warming is, I believe, misleading, exaggerated, or plain wrong. But what are the consensus climate scientists saying that isn’t misleading, exaggerated, or wrong? These are scientists, after all, men and women of high intelligence, years of academic study and, one can assume, high integrity. Surely they can’t be that wrong. What are they getting right?

First, let’s look at what orthodox climate science is arguing. Here’s as good a statement of the consensus hypothesis as any, from R.A. Warrick, E.M. Barrow and T.M.L. Wigley, all recognized climatologists and self-described climate “alarmists” (in Climate and Sea Level Change: Observations, Projections and Implications, from which the hypothesis is taken, they note “the alarming rate of atmospheric concentrations of carbon dioxide”). They write:

The potential rates and magnitudes of the GHG-induced change … give rise to legitimate concerns about the future. These concerns include the following:

  • first, that humankind may now be a potent factor in causing unidirectional global changes which could dominate over natural changes on the decade-to-century time scale;
  • secondly, that, in terms of recent human experience, changes in climate and sea level could accelerate to unprecedented rates;
  • thirdly, that human tinkering with the global climate system could have unforeseen catastrophic consequences (e.g., ‘runaway’ warming or sea level rise from strong positive feedbacks); and
  • finally, that the quickened rates of change could exceed the capacity of natural and human systems to adapt without undue disruption or cost.(1)

In other words, it’s the classic consensus position that the build-up of human carbon emissions rather than natural factors is driving climate change and that we may be heading for disaster. What’s right about this hypothesis?

What’s right is that both carbon dioxide levels in the atmosphere and the global temperature have increased since the mid-1800’s. Also right is that human emissions have been contributing to this increase in carbon dioxide. Finally, it is true that rapid climate changes could have “catastrophic consequences” for humanity.

So, consensus climate science has it right on a number of basic facts. If we go beyond these basic facts, however, the anthropogenic global warming (AGW) hypothesis breaks down rather badly.

Higher carbon dioxide levels are not a danger to life

Carbon dioxide levels have risen in the atmosphere from roughly 280 parts per million in the late 19th century to 380 ppm today, a 30 per cent increase in just over a century. In that time, the global temperature has risen about .8 degrees Celsius.(2) Both represent a fairly rapid increase and human beings are responsible for a small portion of that increase.

But is a CO2 level of 380 ppm dangerous in and of itself, for the planet or for us? Would twice this level be dangerous? Three times? The answer is: not at all, as the consensus climate scientists must be fully aware.  CO2 levels have been much higher in the geological past — often five to 10 times higher (see Figure 1) — and both plants and animals evolved and thrived.(3)

Figure 1: CO2 and temperature levels over 600 million years
Figure 1. Temperature and CO2 levels over 600 million years

A warmer planet is not a danger to life

Is a warmer planet, in and of itself, a danger to life? Again, the answer is no.

For 80 to 90 per cent of its 4.5-billion-year history earth has been warmer, and sometimes up to 15 degrees Celsius warmer, than today.(4) Both the “golden age” of dinosaurs and of mammals occurred when CO2 levels and temperatures were much higher than today’s.

However, our planet is currently in an ice age, and has been for the past two million years. As Figure 1 shows, carbon dioxide levels and temperatures are the lowest in 250 million years, and among the lowest in 600 million years. We are within five degrees Celsius of entering another period of glaciation, which would be very bad news — far worse than an equivalent amount of warming.(5)

So, the consensus position is correct in stating that temperature levels are increasing (until recently — see “Is the planet still warming” on this site) and that CO2 levels are increasing. It is not correct that these increases are, in themselves, a potential “catastrophe.”

Abrupt climate change is a potential danger

Consensus climate science is on stronger ground when it warns that rapid climate change “could exceed the capacity of natural and human systems to adapt without undue disruption or cost.”

The problem for the AGW hypothesis is that rapid climate change has occurred in the past without any human input and will occur in the future regardless of what humanity does or doesn’t do. In addition, the problem facing humanity isn’t rapid climate change, it’s abrupt climate change.

In abrupt climate change, sudden large swings in climate (up to 10 degrees Celsius or more) can occur within a century or even a decade when the climate hits a “tipping point” or trips a “switch” and goes into its opposite mode.(6) For example, this kind of abrupt change occurred 13,000 years ago when the Holocene warming suddenly stopped and temperatures plunged 10 degrees Celsius within a few decades.(7) This event has been called the Younger Dryas minimum. A thousand years later, the temperature rose again almost as suddenly.

Human carbon emissions had nothing to do with these fluctuations. These abrupt changes also prove there is nothing “unprecedented” about the rate of the 20th century’s warming, as the consensus hypothesis would like us to believe.

The climate has never been ‘stable’

In his very readable book Climate Crash, on the science on abrupt climate change, science journalist John D. Cox notes that for the past century climate scientists and geologists have believed that climate change was a slow, gradual, “uniformitarian” process, like the slow creation of mountains. They also believed that “the planet as a whole enjoyed a stable, ‘equable’ climate.”(8)

Instead, Cox writes, analysis of ice cores, ocean sediments, and other climate proxies has revealed that the idea of a stable climate — including in the Holocene, our interglacial — is a myth. Even within the most recent glaciation that ended 15,000 years ago, the climate had rapid spikes of warmth, then sudden plunges back into bitter cold within decades (see Figure 2).(9)

Figure 2: Abrupt climate change during the last glacial
Figure 2: Abrupt climate change during the last glacial

However, as Cox notes, “Climate scientists now realize that just as a moving hand is more likely to throw a switch than a still one, anything that changes the system runs the risk of provoking abrupt climate change.”(10)

Cox’s book is one of those unusual situations where the author’s even-handedness actually disproves the case he wishes to make. Cox argues that increased anthropogenic carbon dioxide levels could trip the climate switch and throw us into a major cold spell, so we should curb carbon emissions.

What he ends up demonstrating is that the planet goes into warm and cold spells far more often than was believed and will continue to do so no matter what we do or don’t do. If we increase carbon dioxide levels, we may trigger an abrupt climate change. On the other hand, even if we decrease carbon dioxide levels, the planet may go into an abrupt cooling anyway due to other triggering factors.

Climate surprises are ‘inevitable’

In other words, any climate factor could trip the switch, or not. As the title of the more scholarly Abrupt Climate Change: Inevitable Surprises tells us, abrupt climate surprises are “inevitable” and we might as well carry on as best we can. The alternative is to go back to living in caves while walking on eggshells lest we waken the climate gods. Like every other creature, we affect the earth — that, too, is “inevitable.”

Once abrupt climate change is understood, the whole issue of trying to curb carbon dioxide to stop anthropogenic warming is seen as irrelevant — the planet will warm or cool as natural forces (not human carbon “forcings”) dictate. This doesn’t mean we shouldn’t seek more efficient, less carbon-emitting forms of energy; it just means that there’s no urgency to do so as far as climate is concerned.

Three unwelcome facts for consensus climate science

Cox also demonstrates three other facts about abrupt climate change that do not support consensus climate science.

First, research into abrupt climate change has shown that climate changes, period, regardless of human activity, and sometimes very rapidly. Consensus climate science, on the other hand, wants us to believe that if it hadn’t been for our emissions, the climate of the past century would have been “stable” rather than warming. For example, an anthology on climate co-edited by Andrew Weaver notes: “Climate change is above all the result of a century and a half of industrialization” [italics added].(11) The clear implication is that without human activity, the climate in the 20th century wouldn’t have changed, or not much. This argument ignores what made the climate start to turn warmer in the mid-1800s, before human carbon emissions were a factor.

Cox’s data shows that this supposed stability is a myth and that thanks to natural variations, the climate in the 20th century would have gone up and down without us — the century’s warming and cooling wasn’t “our fault,” as the consensus would like us to believe.

Second, the abrupt climate change data shows very clearly that what humanity has to fear is not global warming but global cooling. Time and time again, in Cox’s examples such as the Younger Dryas, the negative effects of abrupt climate change — especially drought — result from cooling, not warming. On the other hand, as climatologist William F. Ruddiman notes, “A warmer earth is likely to be a wetter earth.”(12) A warmer, wetter earth is almost always better for humankind.

If consensus climate scientists were arguing that anthropogenic warming could lead to abrupt cooling, they might make some sense (although not entirely: abrupt climate change is clearly dependent on many more factors than human actions, so they’d have to remove the “anthropogenic” part). However, the consensus climate science position, as typified by the Intergovernmental Panel on Climate Change, is that the “tipping point” danger we face is increased warming, period. The University of Victoria’s Andrew Weaver, Canada’s leading climate computer modeler, has written: “Have you heard that global warming may cause an ice age? How ironic. Does it sound odd? It should, as it’s utter nonsense.”(13)

For Weaver and most of consensus climate science, the climate thermometer only goes up because carbon dioxide emissions are going up. Yet, if the abrupt climate change theorists are right — and their ideas are based on fairly conclusive ice core, etc., readings — it’s the consensus position of unlimited, “unidirectional” warming that is utter nonsense.

Human-caused warming may be delaying glaciation

Yes, on average, the planet has warmed in the past 14,000 years because we are in an interglacial. But if and when the switch is tripped, the planet will start cooling, perhaps temporarily, perhaps into the next glaciation, regardless of how much CO2 we put in the air.

Indeed, it’s possible (although unlikely) that human-amplified warming, far from tripping the switch, is postponing the return of the glaciers. In that case, we should be grateful for anthropogenic global warming, rather than trying to stop it.

Third, Cox shows that the current climate models simply cannot handle abrupt climate change: “Abrupt change means that, like the weather itself, climate often behaves in ways that defy prediction.”(14) To make matters worse, orthodox climate science bodies like the IPCC have “focused attention on anthropogenic warming, whereas abrupt climate change is a broader subject covering natural as well as human causes.”(15)

In short — and quite the opposite of the position that he would like to convey — Cox proves that, yes, as the consensus says, climate change could be catastrophic. But he also shows that these abrupt climate changes are beyond human cause or control, and that the consensus climate models are, in effect, useless as predictive tools.

Consensus climate science is more speculation than science

So, summing up, consensus climate science is correct in stating that overall the planet is warming (or rather, it was correct until a decade ago when the warming stopped). It is correct in stating that the level of carbon dioxide is increasing. It is correct in stating that human-caused carbon dioxide may be contributing to this increase. It is correct in stating that climate change could be disastrous.

Beyond this, though, very little of what the consensus hypothesis predicts as a result of human activities has actual scientific evidence to support it. Almost all of the consensus hypothesis is scientific speculation — informed speculation, perhaps, but speculation nonetheless.

In particular, and despite its claims, consensus climate science has failed to show any convincing causal connection between human-caused CO2 and rising temperatures — correlation does not equal causation. After all, global temperatures actually went down from the 1940’s to the 1970’s and the average global temperature has been flat-lined since at least 2001, both while CO2 levels have been rising.

We may have “amplified” some of the past century’s warming but, more likely, the planet would be warming or cooling with or without us thanks to natural variation.

Warming a boon, not a catastrophe

Consensus climate science has also failed to show any causal connection between human-caused CO2 and possible catastrophe — quite the opposite, actually. It’s largely because the planet is warming that we’ve been able to feed a population of more than six billion. In other words, warming has been a boon, not a catastrophe. If catastrophe occurs, it will likely be caused by abrupt climate cooling due to natural variations that are beyond human control, not human carbon emissions and warming.

As for the consensus computer models: they may be useful tools for theoretical analysis but they are not physical scientific evidence and, if abrupt climate change is a reality, they have very little predictive value.

Above all, based on the scientific evidence for abrupt climate change, there are no grounds whatsoever for consensus climate science’s dogmatic condemnation of those — contemptuously called “deniers” — who question that humans are the “driving” force behind global warming and that warming will continue “unidirectionally” until the planet experiences “thermaggedon.” If nothing else, the cooling of 1940-1970 and the non-warming of the past decade have shown that the consensus hypothesis — rising CO2 levels equal rising temperatures — is shaky.

It’s time for consensus climate science to come up with another, more accurate, hypothesis, one that deals with the realities of abrupt climate change, instead of the fairy tale of the “stable” climate that would result if only humanity brought industrial civilization to a halt.


1. R.A. Warrick, E.M. Barrow and T.M.L. Wigley, Climate and Sea Level Change: Observations, Projections and Implications. New York: Cambridge Univ. Press, 1993, p. 3. I’ve converted the paragraph into bullets for easier reading. Although this statement was written in 1993, it holds up very well 15 years later.

2. This is the figure used by James E. Hansen, head of the Goddard Institute for Space Studies and a leading advocate of AGW. See “Why fast action on climate change is needed,” available at

3. This graph and its academic sources are available at

4. Edward Aguado and James E. Burt, Understanding Weather & Climate. Upper Saddle River, NJ: Pearson Education, 2004, p. 479. The authors write: “The majority of the earth’s history has been marked by conditions warmer than those of today.” This is a standard university textbook on climate.

5. Geologist Cesare Emiliani has written, “Temperatures as high as today’s occurred for only about 10% of the time during the past half-million years.” In other words, for 90 per cent of the past 500,000 years, the climate has been glacial. Quoted in John. D. Cox, Climate Crash: Abrupt Climate Change and What It Means for Our Future. Washington, DC: Joseph Henry Press, 2008, p. 81.

6. Committee on Abrupt Climate Change, et al. Abrupt Climate Change: Inevitable Surprises. Washington, CD: National Academy Press, 2002, p. v.

7. John D. Cox, Climate Crash: Abrupt Climate Change and What It Means for Our Future. Washington, DC: Joseph Henry Press, 2008, pp. 24, 41.

8. Cox, Climate Crash, p. 21.

9. Graph is taken from Abrupt Climate Change, p. 37. The data is based on ice cores from Greenland. The Younger Dryas freezing is marked “YD.” See also Science, August 1, 2008, for two articles on abrupt climate change: “High-resolution Greenland ice-core data show abrupt climate change happens in few years,” and “Did you say fast?”

10. Cox, Climate Crash, p. 4.

11. Gerard F. McLean & Murray Love, “Technology and climate change,” in Hard Choices: Climate Change in Canada, Andrew Weaver & Harold Coward, eds. Waterloo, ON: Wilfred Laurier Univ. Press, 2004, p. 127.

12. William F. Ruddiman, Earth’s Climate: Past and Future. New York: W.H. Freeman, 2001, p. 95.

13. Andrew Weaver, “The global cooling fallacy.” Ottawa Citizen, Feb. 18. 2008.

14. Cox, p. 146.

15. Cox, p. 185.