What do we know about global climate change? To begin with, we know the global climate has changed in the past and it will almost certainly change in the future. Significant global climate change is usually assumed to be gradual—over hundreds or thousands of years. However, we have theoretical scenarios that suggest significant changes in global temperatures could occur over a period of decades. The fact that glacial and interglacial periods have lasted several thousand years does not rule out the possibility of a rapid beginning and ending.
Climate Change Theory
The most prominent theory of climate change consists of a positive feed-back system between the amount of atmospheric moisture and thus land covered by winter snow, producing changes in the albedo—reflectivity of solar radiation. Alternating glacial and interglacial events are believed to consist of four cycles. First, a warm-wet period in which higher evaporation increases atmospheric moisture, increasing the northern hemisphere land area covered by winter snow, which increases the albedo and causes temperatures to decline. Second, the cool-wet period in which land areas covered by winter snow increases rapidly, further reducing temperatures, producing glacial advance across northern hemisphere land areas. Third, the cool-dry period when water locked in ice reduces atmospheric moisture and thus winter snowfall, which reduces the albedo and increases absorption of solar radiation. And fourth, the warm-dry period when reduced winter snowfall and higher temperatures produces rapid glacial retreat.
It is possible that glacial and interglacial periods are caused by variations in solar energy associated with changes in earth-sun relationships. Milankovitch, a Yugoslavian astronomer (1879-1954), believed variations in earth-sun relationships produced a 96,000 year climatic cycle. These variations are: a 100,000 year cycle in which the earth’s elliptical orbit about the sun changes from near circular (as it currently is) to a more extreme ellipse; a 40,000 year cycle in which the earth’s orbit “orbits” producing periods when the northern (land) hemisphere is furthest from the sun in January rather than in July (as it is now); and a 26,000 year cycle in which the tilt of the earth’s axis increases from 22 to 24 degrees (currently near maximum at 23.5 degrees). An increase in the ellipsoid, combined with earth being further from the sun in January and a more extreme tilt in the axis, could produce a far greater seasonal temperature change in the northern hemisphere. [Again, note that the southern hemisphere, which of course has the reverse seasonal orientation to the sun, is much less affected because it is mostly ocean which does not experience significant temperature changes from season to season.] Milankovitch’s work was mostly rejected until quite recently, but has now received a substantial measure of confirmation.
It is also possible that massive volcanic activity, a meteor impact, or global nuclear war, could produce or trigger climate global cooling by dust blocking solar radiation. For example, a volcanic explosion in Tambora, Indonesia in 1815 produced the “year without a summer” in the U.S. in 1816 when temperatures below freezing and snow destroyed almost all crops north of the Ohio River, producing mass starvation. The volcano/meteor/nuclear war scenario could theoretically produce or trigger a very sudden reduction in global temperatures.
More recently it has been proposed that human use of fossil fuels can increase “greenhouse effect” which could cause, or increase the pace of, global warming. This theory is unproven, but it merits our attention. We will discuss that theory after considering what is know about past climate change.
How do we know what global temperatures were in the past? We have collected temperature data from about 1860, but these data were, until the advent of satellite imagery, of questionable value. Air temperatures were mostly measured in places that have since been surrounded by cities; the “urban heat island” effect could account for most, or even all, the higher values recorded more recently. Ocean temperatures were measured by hauling a canvas bucket on deck and dropping a thermometer in the bucket; evaporative cooling on the canvas bucket could account for lower temperatures recorded by the older method (we now measure ocean temperatures under water).
We have historical records of farming communities in western Greenland and vineyards in England from 600 to 1350, so we know it was much warmer at that time. We have records of the severity and frequency of drift ice in the vicinity of Iceland from about 1780, as well as paintings showing the variation in elevation of glacial ice in Alpine valleys from 1700 to present. We have biological (such as tree rings) and geological (types of fossils found in rock) evidence, as well as chemical records in glacial ice, that suggest climatic conditions during much earlier periods.
As we move back in geologic time our data can be skewed by the movement of continents by plate tectonics, the rise and erosion of mountain ranges, and shifting of ocean currents.
The evidence provides the following picture of global climate change. First, throughout most of geologic time earth temperatures were MUCH HIGHER than they have been in modern times. The warm periods are referred to as the “Climatic Optimum.” The Climatic Optimum was interrupted by Ice Ages about 600 million, 300 million, and about 1.6 million years ago. Past ice ages lasted for several million years. The most recent Pleistocene Ice Age began about 1.6 million years ago (although there is some evidence that it began as long as 3 million years ago). It consisted of a series of 18 glacial and interglacial periods. The most recent glacial period, referred to as the Early and Main Wisconsin glacial, began about 60,000 years ago and ended about 10,000 years ago. The retreat of the Main Wisconsin glacial may mark the end of the Pleistocene Ice Age, or it could be an interglacial (allowing the glaciers to go back and get more rocks, as some whimsical geologists suggest). From about 5000 BC to 1000 BC global temperatures approached the Climatic Optimum. Although temperatures declined through the Roman period, the northern hemisphere climate remained very mild from about 900 to 1250 AD, a period know as the “Little Climatic Optimum.” The beginning of the Little Ice Age is usually placed at about 1450; this cold period ended in about 1850 and did not produce a major glacial event.
The global climate has been warming since the end of the Little Ice Age in 1850. That statement requires three caveats. First, until very recently most of our data are from the northern hemisphere, or more specifically from Europe and North America. Second, the southern hemisphere, being mostly oceans, will not warm or cool as rapidly as the northern hemisphere; large continental regions warm and cool much more rapidly than do the smaller land areas and we would expect a considerable lag before measurable changes can be noted in the southern hemisphere. Third, short periods of cooling have occurred over the past century and one-half, including the cooling period between 1940 and 1965.
We do not know what caused the Little Ice Age or why it terminated without a major glacial event. Therefore, we cannot know whether or when another major cooling or glacial period could begin. We have very little notion of why the short cooling period occurred in the mid-20th Century, and therefore cannot know whether or when another short cooling period could occur. However, temperatures remain MUCH COOLER than prior to the Little Ice Age, so that the best current guess is that the warming trend will continue. And, it is possible that human use of fossil fuels could increase the greenhouse effect and accelerate this warming trend.
There can be no question about the fact that global temperatures, or at least northern hemisphere temperatures, are currently WELL BELOW the Little Climatic Optimum. From about 900 to 1350 AD, Viking farmers produced wheat in areas of western Greenland that are now covered with permafrost six feet deep. Viking graves, entangled with tree roots, have been found in iron-hard permafrost. Those colonies perished some time after 1350 when they could no longer produce wheat and when iced harbors prevented re-supply or escape by sea. The Viking Greenland colonies are HISTORICAL RECORD; there can be no question about that. We have additional historical data that proves conclusively that northern hemisphere temperatures were higher prior to 1350 than they are today; for example, England had many vineyards for the production of fine wines during that period, which they have not produced since.
Likewise, the Little Ice Age from 1450 to 1850 is a matter of historical record. During this period grain production by Norwegian farmers in Iceland was abandoned (they had long since abandoned grain production in Greenland), and the Thames River near London was frozen hard enough to permit semi-permanent structures during winter months. We have paintings of those structures on the Thames River, and we also have painting showing alpine glaciers much lower than they currently are in the Alps. No knowledgeable individual can deny the fact that the Little Ice Age occurred!
After about 1850 temperatures have tended to increase, but have remained well below those of the “Little Climatic Optimum”, and far below the “Climatic Optimum” that has prevailed throughout most of earth’s history. The trend toward higher temperatures has not been continuous. The cooling period from 1940 to 1965 was noted previously. That short cooling period produced the Ice Age scare that held through the mid-1970’s. Indeed, as late as 1975 there was “a consensus” among environmental scientists that an ice age was imminent (interestingly, this ice age was assumed to result from human use of fossil fuels and pollution). The cooling period ended about 1965 but a couple of cold snowy winters in the eastern U.S. was sufficient to keep the ice age scenario in the front burner through the 1970’s. Alarmist sometimes project the future temperature increase as a continuation of the trend since the nadir of the cool period in the 1940’s. Obviously, a more logical guess would be to assume a continuation of warming since 1850, with the 1940 to 1965 cool period as an anomaly.
Human Role in Climate Change
There is no evidence that human activities caused the Little Ice Age or caused the Little Ice Age to end. Inasmuch as past climate changes have tended to be long-term events, it is reasonable to assume the current warming trend will continue. However, we cannot rule out the possibility of a short-term or even longer-term periods of cooling; indeed, we cannot rule out the possibility that the current warm-wet environment could trigger another glacial event.
Given the current hysteria among “environmentalists”, a few cold years in the eastern U.S. would probably be sufficient to produce a “consensus” that another ice age is imminent. One might assume that people who have preached global warming would be embarrassed to switch to preaching ice age a few years hence. However, they made that switch in the mid-1970’s with no apparent embarrassment. It is important to remember that environmentalists are mostly college professors who get a new crop of students every few years that were not around when the opposite predictions were made. The fact that none of their dire predictions of running out of oil, copper, and other resources, overpopulation induced starvation, erosion of soils in the mid-west, burning pollution filled rivers, desertification, etc., have EVER proven to be true has not deterred them one iota!
CO2 and Global Warming
What do we know about CO2 and climate change? Increases in atmospheric CO2 correlates with higher northern hemisphere temperatures, although some scholars note that the increase in CO2 follows rather than leads warming, so that it may be a result, rather than a cause. We know human use of fossil fuels has released a very large amount of CO2 —indeed, far more than can be accounted for by our measurements of CO2 in the atmosphere. There must be a CO2 sink—probably the oceans and/or a much larger biomass on this earth. It is worth noting that several percent of the earth’s surface is now covered with crops that are heavily fertilized, producing an annual production of biomass per acre that could not have occurred under natural settings. It is conceivable that the massive increase in production of crops and livestock, that currently provides more food per person than ever before to a greatly expanded human population, would not have been possible without the additional atmospheric CO2 released by burning fossil fuels.
[With regard to atmospheric CO2 data, it disturbs me greatly that almost all is collected on Mona Kea in Hawaii, a few miles from a very active volcano that releases huge quantities of CO2. I know the scientists who gather those data are aware of that fact, and I know they are not stupid; I just wish one of them would tell me why they pick that particular, most potentially polluted spot on earth, to gather their data.]
Is it possible that burning fossil fuels could increase atmospheric “greenhouse gases” sufficiently to speed the post Little Ice Age warming trend? YES! Is it possible that the increased warming could cause an increase in sea level and substantial economic dislocation in some areas of the world? YES! Is it possible that warming could produce more and stronger storms and could increase or decrease rainfall amounts in many regions of the world? YES! Global warming would also produce substantial positive effects on the environment in many regions of the world. However, the positive effects of warming will accrue mostly to places that, by definition, do not have humans dependent upon those improved conditions. Perhaps one day people will again produce wheat in western Greenland and fine wines in England, and perhaps many regions of the world that have not supported large human settlements in the past will become habitable. By contrast, the negative effects of climate change will tend to affect the current livelihoods of people and produce economic dislocation immediately.
What is the prudent response when faced with a possible serious threat? We must try to fail-safe; that is, when you must choose between possible errors you must error on the side of the issue that will not result in disaster. By way of (a mundane) analogy, what should we do if the streets are ice covered? Should we postpone a trip to the market or theater? Obviously, YES! Should we be more careful to use our seatbelts and drive more slowly? Obviously, YES? Should we miss a day of work or a final exam? Probably not. Should we refuse to take a seriously injured person to the emergency room? Certainly not!
Does the threat of global warming justify bankrupting our economy and locking half the people in the world into continued poverty? Certainly not! Does it suggest the need to take prudent steps to ameliorate what might be a very serious problem in the future? Obviously, YES! Former President Clinton proposed a 15 cents per gallon tax on gasoline, a small carbon tax, and an increase in mandated mileage requirements for new vehicles. That was a prudent, if modest, response to the “global warming” issue. Unfortunately, the political climate made it impossible for even those modest initiatives to pass congress. Since Clinton’s attempts to deal with this issue, our government has done absolutely nothing meaningful to address this potential threat. What a terrible shame!
It is worth noting that even if “global warming” were a complete hoax (which it is not), we have good reasons to move as quickly as is prudently possible to achieve a more sustainable and eco-friendly energy system. We are not likely to “run out” of fossil fuels in any foreseeable future. But, volatile energy prices greatly damage the world economy, and the some of the major producers of oil are using their profits to murder us! Atmospheric pollution produced by burning fossil fuels costs us a great deal of money and health problems. In addition, a mandated increase in gas mileage on U.S. vehicles appears to be the only way our auto companies will make an effort to become competitive in the U.S. and world auto market. [Isn’t it interesting that Toyota has joined Ford and GM in opposing higher fuel efficiency mandates in the U.S., even though Toyota already exceeds the higher mileage requirements? Do you suppose Toyota knows Ford and GM will not “get off their butts” and begin producing vehicles that can compete unless forced to do so? Do you suppose that Toyota, already the world’s number one automaker, would like to see Ford and GM go bankrupt? You don’t need to be a climatologist or a rocket scientist to figure that out!]
Note: Much of the data for this section is taken from “Climate Change”, Chapter 7 in Applied Physical Geography, Oliver, Stover, Nellis, & Bussing, Kendall/Hunt Publishing, 1990. The remainder is gleaned from various works in geography and history.