Ice cores have revealed that very large climate swings can occur over just a few years—at least they have in the past. Civilized humankind has not experienced such events. The last one, the Younger Dryas, occurred about twelve thousand years ago. Cooling our climate to glacial temperatures over just a few years would severely disrupt global food production and render cities far from the equator uninhabitable. The ice core record from central Greenland shows that events like the Younger Dryas were the norm for most of the last 100,000 years, while the time corresponding to human recorded history has been quite exceptional.80 Extending the record further back in time with the less detailed Antarctic ice cores, it appears that the present warm period is the longest-lived one of the past 420,000 years. There’s clearly something special about our time.
80The paleoclimate records of the past half-million years show that the times of greatest climate stability are the relatively short-lived “peak interglacials,” like the one we are presently living in (though ours is already longer-lived). See J. P. Helmke et al., “Sediment-Color Record from the Northeast Atlantic Reveals Patterns of Millennial-Scale Climate Variability During the Past 500,000 Years,” Quarternary Research 57 (2002): 49-57, and J. F. McManus, et al., “A 0.5 Million-Year Record of Millennial-Scale Climate Variability in the North Atlantic,” Science 283 (1999): 971-974. Using otoliths (bony structures in fish for acoustics and balance) as temperature proxies, the following study determined climate conditions about 6,000 years ago: C. F. T. Andrus, “Otolith 180 Record of Mid-Holocene Sea Surface Temperatures in Peru,” Science 295 (2002): 1508-1511. They showed that sea temperatures were three to four degrees Centigrade warmer and El Niño events less severe at that time.
These records provide an objective test of computer simulations, which otherwise can be highly subjective. Climatologists can now develop long-term simulations of the global climate by adjusting their models to the present climate and testing them on the paleoclimate data derived from the diverse Earthly archives.81 With this growing database, they’ll continue to improve their ability to predict future climate changes. Long-term forecasting once seemed a dream, but the ice-filled pipes of ice cores, alongside other records, may one day make that dream a reality.
81For instance, they consider such factors as carbon dioxide concentration, global ice volume, atmosphere and ocean circulation, solar variations, and the Milankovitch cycles.
We still have much to learn about climate change, of course, but one surprising discovery from this work is that atmospheric carbon dioxide could help prevent glaciation in the future. Research by climatologists A. Berger and M. Loutre of the Institut d’Astronomie et de Geophysique in Belgium suggests that variations in the average amount of sunlight received recently by the Northern Hemisphere are quite exceptional.82 They compared the near-term changes (due to the Milankovitch cycles), five thousand years back to sixty thousand years into the future, to those of the past three million years. They found that only five intervals in the past three million years had variations as moderate as our present.83
82In their study “Future Climatic Changes: Are We Entering an Exceptionally Long Interglacial?” Climatic Change 46 (2000): 61-90, they stated, “This insolation variation…is really exceptional and has very few analogues in the past.”
83If the Milankovitch astronomical cycles are the main driving force of the ice ages, this could help explain the highly anomalous climate stability of the Holocene, the past twelve thousand years. But there’s more going on, because Berger and Loutre predict moderate variations up to sixty thousand years into our future. Moreover, the observed range of the Milankovitch variations since the start of the Holocene has been surprisingly small. Their prediction seems well founded, but there seems to be more going on than they realize. Their explanation for the stability of the Holocene is the low amplitude of the Milankovitch cycles from five thousand years ago until sixty thousand years into the future, compared to the past three million years or so. This seems to be an odd coincidence. But how can you use the predicted changes in the future as part of the explanation for the anomalous stability of the Holocene so far?
Loutre and Berger also found that for up to 130,000 years into the future, the onset of a glaciation depends on the atmospheric level of carbon dioxide, with less carbon dioxide leading to more pronounced growth of ice sheets in the Northern Hemisphere.84 So not only has the climate been anomalously warm, with fairly stable temperatures for the last twelve thousand years, but we could enjoy stability for at least a few tens of thousands of years into the future. That puts us at the beginning of a long-lived stable, warm period.
84A concentration below 260 parts per million by volume seems necessary for substantial glaciation prior to 50,000 years from now. Right now it’s at 370 parts per million.
You’re probably astonished to learn that a high carbon dioxide level could inoculate the planet, and us, against a near-term glaciation (as long as it’s not too high, of course). The modern Industrial Revolution has maintained, and will continue to maintain, carbon dioxide levels well above the minimum threshold Loutre and Berger predict.85
85Some have argued recently that the Atlantic Ocean circulation can be disrupted by the rapid injection of fresh water into the North Atlantic from the discharge of large numbers of icebergs as the polar ice breaks up during a rapidly warming period (as some predict for the next century), supposedly returning us to glacial conditions in short order (Alley and Bender, “Greenland Ice Cores,” 181-184). This is a factor Loutre and Berger did not include in their models, but if it occurs, it’s likely we can recover from it quickly with a high carbon dioxide level. In any case, support among climatologists for themohaline circulation as a driver for the ocean currents is losing ground to wind and lunar tides as the main driving forces. See C. Uhlmann et al., “Warming of the Tropical Atlantic Ocean and Slow Down of Thermohaline Circulation During the Last Deglaciation,” Nature 402 (1999): 511-514.
Even within the framework on the thermohaline circulation model, the most recent atmosphere-ocean circulation simulations suggest that the feared shutdown of the ocean circulation from greenhouse warming will not occur. See M. Latif et al., “Tropical Stabilization of the Thermohaline Circulation in a Greenhouse Warming Simulation,” Journal of Climate 13 (2000): 1809-1813; S. Sun and R. Bleck, “Atlantic Thermohaline Circulation and its Response to Increasing CO2 in a Coupled Atmosphere-Ocean Model,” Geophysical Research Letters 28 (2001): 4223-4226.
We should be glad that the era since the last glacial period has lasted this long. You might not be reading this book had the next major glacial period started, say, one thousand years ago.86 The Northern Hemisphere’s climate would have been too severe for Europe to drag itself out of the so-called Dark Ages and to give us enough leisure time to make the web of scientific, philosophical, and artistic advancements that laid the ground-work for the Scientific and Industrial Revolutions. And without industrial man pouring his extra carbon dioxide into the atmosphere by burning fossil fuels, as he began to do some 150 years ago, the tendency toward increased glaciation might have continued unchecked, making it more and more difficult for civilization to progress. Carbon dioxide emissions are the natural consequence of the rise of civilization (in fact, concentration of carbon dioxide tracks closely with world population).
86Even during the relatively stable Holocene, the era since the Younger Dryas, temperatures have fluctuated enough to disturb civilizations. Earth is still recovering from a centuries-long cold spell that ended in the early nineteenth century, although the rising carbon dioxide should delay the next cold spell.
Human activity has always affected our planet locally, but our striving since the early Holocene has brought us to the point where we can hope to understand the global climate system just as we’re beginning to have a significant impact on it.87 If we’re smart, the measurability of our environment can lead to improved habitability in the near term by allowing us to attune our behavior with the natural processes of global change.88
87We must interpret this data properly if we are to avoid costly and even deadly mistakes, especially since the actual effects of our activities may sometimes be counterintuitive. For instance, this evidence suggests that hindering worldwide economic growth for a slight reduction in the global temperature is unlikely to make Earth more habitable for life in general. In fact, it would probably have the opposite effect, by making it much less hospitable for civilization. We agree with Peter Huber [Hard Green: Saving the Environment from the Environmentalists, A Conservative Manifesto (New York: Basic Books, 1999)] that a healthy economy leads to a healthy environment. In addition, there is a huge (and rapidly growing) volume of published material demonstrating the many benefits to the biosphere and to civilization of elevated carbon dioxide levels. Most of the benefits would come from the effects of aerial fertilization on plants and trees. For a review of this topic, see C. D. Idso, “Earth’s Rising Atmospheric CO2 Concentration: Impacts on the Biosphere,” Energy & Environment 12 (2001): 287-310. The increased plant growth resulting from higher carbon dioxide levels will greatly aid in food production in the coming century as population grows. The overall climate would also be more hospitable. For example, the growing season in cold latitudes would be lengthened; the warming is expected to occur mostly in the winter and nights; evaporation and precipitation would increase, probably resulting in more rainfall throughout the world and more snowfall in artic regions.
The moderate increase in global temperatures, too, should benefit civilization. This is not just unfounded speculation. The effects of the climate fluctuations of the past millennium support the notion that warm periods are preferable for civilization. The Medieval Warm Period, also called the Little Climate Optimum, peaked near A.D. 1200, reaching perhaps half a degree centigrade higher temperatures than the present. Afterwards, the Little Ice Age saw its coldest temperatures in the seventeenth century. There is much historical anecdotal evidence that the Little Ice Age was much harsher on European peoples than the Medieval Warm Period. For a historical treatment, see H. Lamb, Climate, Change, and the Modern World, 2nd ed. (London: Routledge, 1995). There is also increasing evidence that the Medieval Warm Period and Little Ice Age were global phenomena. If the many predicted catastrophes resulting from warmer temperatures (such as the shutdown of the Atlantic circulation of the sudden release of methane from the ocean floor) did not already occur during the Medieval Warm Period (or during the even warmer “Holocene maximum,” about five thousand years ago), then they are not likely to occur in the coming centuries either.
88The notion that we are conducting a vast and dangerous experiment on the climate is often repeated in apocalyptic environmentalist literature. The quote “Through his worldwide industrial civilization, Man is unwittingly conducting a vast geophysical experiment” was an early expression of this view. It originated in R. Revelle, W. Broeker, H. Craig, C. D. Keeling, and J. Smagorinsky, “Restoring the Quality of Our Environment,” Report of the Environmental Pollution Panel, President’s Science Advisory Committee (Washington, D.C.: The White House, 1965), 126. People who hold to this view never imagined that the activities of industrialized society could benefit the world’s ecosystems.
from “Privileged Planet” by Dr. Guillermo Gonzalez & Dr. Jay Richards.
The Cost of Discipleship by Dietrich Bonhoeffer
