“Far from being self-stabilizing, the Earth’s climate system is an ornery beast which overreacts even to small nudges.”
by Ian Angus
|“Human civilization developed during the Holocene (the past 12,000 years). It has been warm enough to keep ice sheets off North America and Europe, but cool enough for ice sheets to remain on Greenland and Antarctica. With rapid warming of 0.6°C in the past 30 years, global temperature is at its warmest level in the Holocene. … Earth’s paleoclimatic record tells us that atmospheric greenhouse gases are now near the dangerous level where tipping points become unavoidable.” –James Hansen |
To judge by many accounts of climate change, the twenty-first century will gradually become a warmer, stormier, and less biodiverse version of the twentieth. There’s an unspoken assumption that the Anthropocene will be less pleasant than the Holocene, but not fundamentally different, and that the transition will be smooth. As research commissioned by the U.S. National Research Council points out, that assumption leads to particular conclusions about society’s ability to respond to change:
“Many projections of future climatic conditions have predicted steadily changing conditions giving the impression that communities have time to gradually adapt, for example, by adopting new agricultural practices to maintain productivity in hotter and drier conditions, or by organizing the relocation of coastal communities as sea level rises.”
But the authors emphasize that the actual experience could be very different:
“The scientific community has been paying increasing attention to the possibility that at least some changes will be abrupt, perhaps crossing a threshold or ‘tipping point’ to change so quickly that there will be little time to react. This concern is reasonable because such abrupt changes – which can occur over periods as short as decades, or even years – have been a natural part of the climate system throughout Earth’s history. The paleoclimate record – information on past climate gathered from sources such as fossils, sediment cores, and ice cores – contains ample evidence of abrupt changes in Earth’s ancient past, including sudden changes in ocean and air circulation, or abrupt extreme extinction events.” 
Many Earth System scientists argue that abrupt environmental change isn’t just possible, but virtually certain:
“In reality, Earth’s environment shows significant variability on virtually all time and space scales. … Nonlinear, abrupt changes in key environmental parameters appear to be the norm, not the exception, in the functioning of the Earth System. Thus, global change is not likely to be played out as a steady or pseudo-linear process under any conceivable scenario but will almost surely be characterized by abrupt changes for which prediction and adaptation are very difficult.”
The imbalance of nature
The idea that the natural world is fundamentally stable and unchanging has a long history. In its oldest version, it is religious: God created a perfect world, and if humans disturbed that perfection, God would in time restore it. A secular equivalent was expressed in 1864 by the pioneering U.S. naturalist, George Perkins Marsh:
“In countries untrodden by man, the proportions and relative positions of land and water, the atmospheric precipitation and evaporation, the thermometric mean, and the distribution of vegetable and animal life, are subject to change only from geological influences so slow in their operation that the geographical conditions may be regarded as constant and immutable.”
That view remains influential: one of the most quoted passages in all naturalist literature is Aldo Leopold’s 1949 call for a “land ethic” based on preserving the “integrity, stability and beauty of the biotic community” – it doesn’t seem to have occurred to Leopold, or to his contemporary admirers, that the natural world might be naturally unstable, subject to rapid change even in the absence of human activity.
Naturalists had of course been aware since the mid-19th century that glaciers had at least once advanced to cover much of the world with ice, and that animals now unknown once walked the earth, but changes of that magnitude were believed to occur extremely slowly, and to be of no relevance to human history and activity. Like the painted backdrop in a stage play, the natural world was unchanging context, not an active player in any human drama.
That view is no longer tenable. Scientific research now shows that the Earth is constantly changing on every scale of space and time, and that the most drastic changes often occur with remarkable speed.
In 2004, synthesizing a decade of Earth System research, scientists from the International Geosphere-Biosphere Program wrote:
“The behavior of the Earth System is typified not by stable equilibria but by strong non-linearities, whereby relatively small changes in a forcing function can push the System across a threshold and lead to abrupt changes in key functions. Some of the modes of variability noted above contain the potential for very sharp, sudden changes that are unexpected given the relatively small forcing that triggers such changes. … The potential for abrupt change is a characteristic that is extremely important for understanding the nature of the Earth System. The existence of such changes has been convincingly demonstrated by paleo-evidence accumulated during the past decade.”
Much of that paleo-evidence comes from new methods of extracting and analyzing deep cores from glaciers in which ice has been accumulating in layers for millennia. Two cores, each over 3,000 meters deep, were drilled in Greenland in the early 1990s – they provided a record of atmospheric conditions going back 100,000 years. Later in the nineties, an international team working in the Vostok region of Antarctica extracted and analysed a core that was 420,000 years old at its deepest point. It is no exaggeration to say that this research has revolutionized our understanding of Earth’s past.
The graph below, adapted from a study of ice-core data by scientists at the Potsdam Institute for Climate Impact Research, shows the average annual temperature in Greenland over the past 100,000 years. Our current epoch, the Holocene, is at the top right.
The first 90% of this time was the end of the Pleistocene, a 2.6 million year-long epoch characterized by repeated glacial advances and retreats: the global climate was not only cold, it was extremely variable. Modern humans walked the Earth for all of the time shown in this graph, but until the Holocene they all lived in small nomadic groups of hunter-gatherers. Climate historian William J. Burroughs, who calls that time the reign of chaos, argues compellingly that so long as rapid and chaotic climate change was the norm, agriculture and settled life were impossible, even in parts of the world that the glaciers never reached. To succeed agriculture needs not just warm seasons, but a stable and predictable climate – and indeed, in just a few thousand years after the Holocene began, humans on five continents independently took up farming as their permanent way of life.
“Once the climate had settled down into a form that is in many ways recognizable today, all the trappings of our subsequent development (agriculture, cities, trade etc.) were able to flourish.”
For over 10,000 years, the average annual global temperature has not varied by more than one degree Celsius – up or down half a degree. But averages can conceal substantial variations: despite being warm and stable on average, the Holocene has not been an unmitigated climate paradise. A one-degree average temperature range has been great enough to include uncounted massive droughts, famines, heat waves, cold snaps and intense storms, extreme weather events in which millions of people died.
But the Pleistocene was far worse: temperature variations were five to ten times greater than anything humanity has experienced since. What’s more, the transition from Pleistocene cold to Holocene warmth was itself an abrupt and chaotic process. Geologists Jan Zalasiewicz and Mark Williams write:
“Coming from the Glacial Maximum, temperatures suddenly rose, 14,700 years ago, with the average temperature of the north Atlantic and surrounding areas increasing rapidly by some 5°C (over Greenland, the temperature hike approached 20°C). Temperatures remained around these levels for nearly two millennia – and then fell suddenly by a similar amount, as the whole region went into a deep freeze once more. …”
The new cold period, known to geologists as the Younger Dryas, lasted a thousand years.
“Then, 11,700 years ago, temperatures suddenly soared again in another climate transformation – only this time the warm temperatures stayed, and this transition marks the beginning of the Holocene.”
How sudden is sudden? Each of the temperature jumps took a few decades to complete, almost no time in geological terms. But what’s truly astonishing is that in both cases the actual tipping point, the change in atmospheric circulation that drove the warming, “seems to have been accomplished in something between one and three years.”
From Holocene to Anthropocene
In 1999, the first scientists to study the Vostok ice core reported with surprise that “the Holocene, which has already lasted 11,000 years, is, by far, the longest stable warm period recorded in Antarctica during the past 420,000 years.”
Now, most Earth Scientists agree that human activity has made changes that are “overwhelming the great forces of nature,” ending the Holocene and giving birth to a new geological epoch, the Anthropocene.  The question is, will this transition be gradual, or can we expect sudden shifts comparable to those that initiated the Holocene?
The specific causes of past climate chaos are unlikely to repeat, so the pattern of change will certainly be different. But the most significant difference between then and now is the unprecedented impact of human activity in the past 60 years – and that makes it very likely, as a team headed by the noted U.S. biologist Anthony D. Barnosky recently concluded, that the Earth is “approaching a state shift.”
“Comparison of the present extent of planetary change with that characterizing past global-scale state shifts, and the enormous global forcings we continue to exert, suggests that another global-scale state shift is highly plausible within decades to centuries, if it has not already been initiated.”
If that occurs, the relative stability of the Holocene could be replaced by a new and unprecedented climate state, unlike anything any human society has experienced. And as noted geoscientist Richard B. Alley points out, the transition is likely to be fast.
“Large, abrupt climate changes have repeatedly affected much or all of the earth, locally reaching as much as 10°C change in 10 years. Available evidence suggests that abrupt climate changes are not only possible but likely in the future, potentially with large impacts on ecosystems and societies….
“Surprising new findings [show] that abrupt climate change can occur when gradual causes push the earth system across a threshold. Just as the slowly increasing pressure of a finger eventually flips a switch and turns on a light, the slow effects of drifting continents or wobbling orbits or changing atmospheric composition may ‘switch’ the climate to a new state. And, just as a moving hand is more likely than a stationary one to encounter and flip a switch, faster earth-system changes – whether natural or human-caused – are likely to increase the probability of encountering a threshold that triggers a still faster climate shift.”
Alley says that abrupt changes are most likely to occur in times when the climate system is under extreme stress, as it is today.
“Abrupt climate changes were especially common when the climate system was being forced to change most rapidly. Thus, greenhouse warming and other human alterations of the Earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events. The abrupt changes of the past are not fully explained yet, and climate models typically underestimate the size, speed, and extent of those changes. Hence, future abrupt changes cannot be predicted with confidence, and climate surprises are to be expected.”
Scientists associated with the International Geosphere-Biosphere Program warn that abrupt climate changes are particularly dangerous.
“Societies can have little or no warning that a forcing factor is approaching such a threshold, and by the time that the change in Earth System functioning is observed, it will likely be too late to avert the major change.”
Wallace Broecker, known as the dean of American climate scientists, is more concise and dramatic:
“The paleoclimate record shouts out to us that, far from being self-stabilizing, the Earth’s climate system is an ornery beast which overreacts even to small nudges.”
This year, atmospheric carbon dioxide rose to 403 parts per million, compared to a maximum of 280 during the wildest climate swings of the Pleistocene. That’s much more than a small nudge, so no one should be surprised if the ornery beast strikes back violently, again and again. And no one should be surprised if the result is a world unlike anything humanity has ever seen.
To prevent that, or at least minimize its effects, the first thing to do is to stop poking the beast.
This article is one of several I’m writing on aspects of the Anthropocene and its implications for ecosocialists. This is a new subject for the left, and the science is evolving rapidly, so my judgments are preliminary and subject to change. I look forward to receiving comments and suggestions. – Ian
Ian Angus is editor of the ecosocialist journal Climate & Capitalism, and co-author of Too Many People? Population, Immigration, and the Environmental Crisis (Haymarket 2011)
 James Hansen. “Tipping point: Perspective of a climatologist.” in State of the Wild 2008-2009. Eva Fearn, ed. Washington: Island Press, 2008. 6-15
 James White et al. Abrupt Impacts of Climate Change: Anticipating Surprises. Washington: National Academies, 2013. 8
 Will Steffen et al. “Abrupt Changes: The Achilles’ Heels of the Earth System.” Environment: Science and Policy for Sustainable Development 46.3 (2004) 9
 George P. Marsh. Man and Nature, Or, Physical Geography as Modified by Human Action. New York: Charles Scribner, 1864. 34
 Aldo Leopold. A Sand County Almanac With Other Essays on Conservation from Round River. (1949). Enlarged ed. New York: Ballantine Books, 1970. 262
 Will Steffen, et al. Global Change and the Earth System: A Planet under Pressure. Berlin: Springer, 2004. 83
 A. Ganopolski, S. Rahmstorf, “Rapid Changes of Glacial Climate Simulated in a Couple Climate Model,” Nature 409, January 11, 2001. 153–58.
 William J. Burroughs. Climate Change in Prehistory: The End of the Reign of Chaos. Cambridge University Press, 2005. 13, 102.
 Jan Zalasiewicz and Mark Williams. The Goldilocks Planet: The Four Billion Year Story of Earth’s Climate. Oxford University Press, 2012. 204
 Ibid. 205. Emphasis in original
 J.R. Petit, et al. “Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica.” Nature 399, June 3 1999. 429-436
 Steffen, Will, Paul J. Crutzen, and John R. McNeill. “The Anthropocene: Are Humans Now Overwhelming The Great Forces Of Nature.” AMBIO: A Journal of the Human Environment 38.8 (2011) 614-21
 Anthony Barnosky et al. “Approaching a State Shift in Earth’s Biosphere.” Nature 486 (2012)
 Richard B. Alley et al. Abrupt Climate Change: Inevitable Surprises. National Academy Press, 2002. v
 Ibid. 1.
 Will Steffen et al. Global Change and the Earth System. 235
 Wallace Broecker. “Cooling for the tropics.” Nature 376, July 29 1995. 212-3