A Long-Term Perspective on Global Temperatures

A while back I read the book Unstoppable Global Warming Every 1,500 Years by S. Fred Singer and Dennis T. Avery (Rowman and Littlefield Publishers, 2007). This book marshals a wealth of information about past temperature changes on Earth. The awesome power of those temperature changes and some of the consequences for mankind are important lessons for us all to learn.

In their review of the ancient climate history, they note 100s of millions of years when the Earth was very much warmer than today. A mere 2 million years ago, the Earth settled into a pattern due to the Earth's orbit and relationship with the sun of Ice Ages lasting commonly 90,000 to 100,000 years. These were terminated with brief warm periods or interglacials of 10,000 to 20,000 years length. The onset of the glacial periods is slow, but the end of an Ice Age is often abrupt. The average global temperature rises 5 to 7 degrees Celsius in the interglacial period.

The last Ice Age was at its coldest about 17,000 to 21,000 years ago. About 14,000 years ago there was a sudden temperature increase. The ice sheet began retreating and sea levels began to rise. About 12,500 years ago, there was a return to a new Ice Age called the Younger Dryas, with the cooling occurring in a mere 100 year timespan. 11,500 years ago there was another sudden warming, producing the present interglacial period, called the Holocene. Following this, much of mankind was able to make significant advances in knowledge and technology.

The Climate Optimum was from 9,000 to 5,000 years ago and most of the Earth was warmer and wetter than it is today. There may have been a brief colder and drier period about 8,200 years ago, which especially affected Africa. About 2,600 years ago, there was a cooling, though the period stayed humid.

More recently, from 600 to 200 BC, there was a cool period. This was followed by the Roman Warming from 200 BC to 600 AD. The Dark Ages were characterized by another cold period, which contributed to an increase in human misery, lasting from 600 to 900 AD. This was followed by the Medieval Warming (or the Little Climate Optimum) from 900 to 1300. Then from 1300 to 1850 mankind suffered through the Little Ice Age, which had a slight warming period (1400 to 1550) which still left temperatures below the recent temperature averages.

Since the end of the Little Ice Age, the Earth's temperature has continued to undergo temperature cycles. From 1850 to 1940 there was warming, with a particularly large temperature increase from 1920 to 1940. From 1940 to 1975 there was cooling and many experts were worrying about or predicting the onset of the next Ice Age. In 1976 and until 1978, there was a sudden warming. Since 1979, surface thermometers on land have shown a significant warming but weather balloons and satellites have shown much less warming. To this, we can add that from 1999 to the present, there has been a slight cooling. If you reference this interval to 2001, there has been no net change in surface temperature.

The Global Warming alarmists are fond of talking about the increase in temperature since 1850 or what they call the start of the Industrial Age. Or they start the clock in 1900 or in 1975 when warming cycles were underway. What they never point out to the reader or listener is that other periods as warm or warmer have played an important role in man's history. They also do not point out that man commonly flourished best in these warmer periods, such as the Roman Warming (Greek and Roman civilizations), the Medieval Warming when food production increased and so did the human population, and certainly man has prospered and the population has grown tremendously since 1850 and the end of the Little Ice Age. Perhaps a little warming is a good thing!

There is a great document called A Global Warming Primer produced by the National Center for Policy Analysis, which gives a graphic presentation about greenhouse gases, tracks temperatures back for 600 million years, and tracks CO2 concentrations in the atmosphere back 550 million years. This gives a perspective on the ability of the Earth to change its temperature readily without the help of man. It also shows that through most of these years, the amount of CO2 in the atmosphere and the average temperature of the Earth do not track one another! So, there are mechanisms to bring about large temperature changes which do not depend upon carbon dioxide concentrations. Through most of this period, the Earth's temperature and its CO2 concentrations in the atmosphere were much higher than they have been in the last 400,000 years.

However, in the last 400,000 years, there has been a correlation between the CO2 levels and the average temperature. But, we are not sure which serves as the cause and which is the effect. The CO2 concentrations and the temperature appear to have about a 120,000 year cycle in this time, which is about the same as that due to adding the glacial periods to the interglacial periods. Clearly, man was not causing these cycles. Presently, the CO2 levels are high compared to other times in this short 400,000 year period, but there is a time in each of the previous 4 cycles, when the CO2 concentrations were comparable or higher.

More recently, the CO2 concentration has steadily increased since about 1760, with a generally increasing rate since 1850. The temperature has mostly increased since then, but its curve does not have the shape of the CO2 curve. The CO2 increase has been rapid since 1950, but as we discussed above, the temperature was cooling from 1940 to 1975. There was certainly a failure to show correlation in that time frame.

Recently, it has become clear that increases in CO2 tend to bring on increases in water vapor and that this usually results in sufficient cloud cover that sufficiently more sunlight is reflected off into space to cause a cooling response to increased levels of CO2. This is still not a well-understood effect. Water vapor itself is a greenhouse gas and makes up 95% of all greenhouse gases in the atmosphere. But, when it forms clouds, they help to hold heat in at night while reflecting the heating rays of the sun in the daytime. The empirical evidence is that increasing water vapor seems generally to lead to a cooling effect. Part of this is due to the heat absorbed by a water molecule in becoming a vapor rather than liquid. The other part is the added reflectivity of the clouds.

A Global Warming Primer also gives a chart to show the Per Capita emission of CO2 by country. The U.S. is one of the highest per capital emitters, but Australia and Canada are not far behind. We are considerably higher than Germany, France, and the United Kingdom. I wonder what is the reason for this grouping. Perhaps it has to do with the density of the population, the expanse of the country, and the amount of farming done. Note that Australia and Canada, like the U. S., do considerable farming, they are big, expansive countries, and people are scattered over large distances. Well, just shoot us all for living where we do! Oh, and while we are at it, how about the rest of the world doing without the huge amounts of food that we produce and export. It costs a lot of energy to produce so much food. It is also interesting to look at the chart that shows how U. S. CO2 emission increases compare with those of the European Union in recent years. The E. U.s increases are much greater.

There are also charts showing sea level rise, the range of estimates for ice mass loss or growth in Greenland and Antarctica, the number of hurricanes by category of severity, and the number of weather-related deaths which seems to have peaked in the 1920s and 1930s when we had a previous high temperature spell, but have been much lower in the recent supposed period of increased temperature. There is a chart showing the U. S. land area affected by droughts since 1895, showing peaks in the 1930s, the late 1950s, and then again in early 1990s. The late 1950s were a cooling period, so there is no correlation here with rising temperatures. There is also a chart showing the benefits of increased CO2 levels for plants, especially those with suboptimal water. Then there are charts showing how little effect the Kyoto Protocol will have on temperature change, malaria, hunger, and coastal flooding.

The perspective given by all of these facts should make us hesitant to accept the claim that man is causing global warming by emitting CO2, without clear and certain evidence that this is the case. A few half-baked computer models which cannot predict the temperatures of the past should not be trusted to predict those of the future and to dictate policy with respect to reductions in our individual rights. If you want to reduce my rights, you had better have a very strong, rational argument for doing so. Do not attempt this with the flimsy arguments of the anti-man Global Warming alarmists.