VI. CLIMATIC CHANGE
Encyclopedia Britannica Copyright 1964
Geographical history is divided into four main periods, Precambrian (Archeozoic and Proterozoic), Paleozoic, Mesozoic and Cenozoic (Tertiary and Quaternary). There is evidence of many changes of climate, but this article is mainly limited to those which occurred after the appearance of man, roughly a million years ago, at the beginning of the Quaternary. The Tertiary is divided into Eocene and Paleocene, Oligocene, Miocene and Pliocene; the Pleistocene is in the Quaternary. The Tertiary began about 70,000,000 years ago, with warm climates and this period was one of the gradual cooling which became rapid toward the end. The uppermost beds of the Pliocene contain large numbers of Arctic species, and appear to be contemporaneous with the first glaciations of Scandinavia and the Alps.
The latest bed in England which was formerly attributed to the Pliocene, the Cromer Forest bed, indicates a return of somewhat warmer conditions and is now placed in the first interglacial period. It is succeeded by boulder clays and other deposits of land ice, indicating the oncoming of glacial conditions in England.
1. Quaternary Ice Age- The Quaternary Ice Age was characterized by the advanced of great glaciers or ice sheets from a number of centres, of which the most important were Scandinavia and the Alps in Europe and the Cordilleras and various other centres in North America. Minor centres of glaciation were located in Spitsbergen, Iceand, Ireland, Scotland and northern England, the Pyrenees, the Caucasus range, the Himalayas, the mountain ranges of central Asia, Alaska, and the whole chain of the Rockies and Andes, the highest mountains of equatorial Africa, New Guinea, southeastern Australia, and New Zealand.
The ice sheets of Greenland and Antarctica are remnants of the Quaternary glaciation, and illustrate the character of the great inland ice sheets of northern Europe and North America.
The maximum area occupied by land ice was about 13,000,000 square miles, including 5,000,000 square miles in the Antarctic, 4,500,000 square miles in North America, 1,250,000 square miles in Europe and at least as much in Asia, and over 800,000 square miles in Greenland. The present area is about 6,000,000 sq.mi. In addition, there was a great extension of floating ice in the oceans, especially in the North Atlantic and Antarctic. Altogether, nearly one-tenth of the earth’s surface must have been ice covered. The ice did not reach its maximum thickness and extension simultaneously; if it had, the amount of water withdrawn from the oceans would have lowered the sea level by almost 400 ft. The actual lowering however exceeded 260 ft., which is sufficient to show that the major ice sheets were all in existence at the same time.
2. Pluvial Periods- In tropical and subtropical land areas the rainfall during the glacial periods and almost everywhere greater than during the interglacial periods. In North America the lakes of the Great Basin spread out to form the large inland seas, the best known of which are Lahontan and Bonneville. In east Africa a whole series of lakes has been found and correlated with the Alpine sequence: Kafuan with the Gunz and Mindel; Kamasian with the Riss; and Gamblian, consisting of four successive lakes, the first three representing the three maximums of the Wurm. The pluvial periods were separated by the interpluvials, during which the lakes dried up more or less completely.
3. Postglacial Period- The postglacial period was marked by alternations of rainy and dry climates. These are clearly shown in peat bog sections by the alternation of rapid growth and drying up, often with tree growth. The succession was first investigated and the periods named by the Norwegian Axel Blytt; in later years G. Erdtman and H. Godwin carried the study into great detail. The rainy Atlantic period was followed by the Subboreal. This was on the whole cooler and drier, with long droughts in which the surface of the peat dried up, followed by returns to more rainy conditions.
The main dry periods were about 2200-1900, 1200-1000, and 700-500 B.C. The latter was the best developed; it has been described as a dry heat wave lasting for perhaps 200 years. Lakes decreased in area and in a few places trees grew on their floors below the level of the outlet. From four such lakes in Ireland, Germany and Austria it is estimated that the rainfall was only about half that of recent centuries. The drought was not intense enough to interrupt the steady development of the forests, but it caused extensive migrations of peoples from drier to wetter sites. At the end of this dry period, about 500 B.C., there was a rapid deterioration of favourable climate, marked by renewed growth of sphagnum bogs and flooding of lake settlements; this brought in the Sub-Atlantic period.
4. Climatic Changes During the Christian Era- Increasingly detailed and accurately dated knowledge of climatic changes began with the Christian Era. In Europe this depends on peat bogs, lake levels, advances and retreats of glaciers, location of settlements and, later, literary records and old weather journals. In Asia the prime source is the level of the Caspian sea; Chinese annals are also helpful. In northeast Africa there are the levels of the Nile and the history of oases. In the west of North America the rainfall is recorded with surprising accuracy by the widths of the annual tree rings. These varied lines of evidence from the north temperate zone are in general agreement, with some differences of detail.
At the beginning of the Christian era the climate was much as it is at present, or possibly a little rainier, especially in northeast Africa. About A.D. 400 a period of relative warmth and dryness set in, the Caspian sea being below its present level. This dry period reached its greatest intensity about A.D. 700, when there was much traffic off western Europe, and the civilization of Ireland reached a high level. There were many droughts in China, low Nile levels, and a great decline in the prosperity of the north African oases. Ellsworth Huntington’s curve of the tree growth in western America fell to a very low level; this dry period in America is supported by some evidence of lake levels.
After about 800 A.D. the climate of the temperate belt became rainier, but remained mild. Greenland was explored and colonized in the 10th century under conditions far more favourable than those of the 20th century.
Western Europe became stormy after 1200, and there were many inundations of the North sea coasts of England and the Netherlands, culminating in the destruction of Winchelsea and the coastal defenses of the Netherlands and Frisia. In Greenland, where the Norse colonies had prospered in the 11th and 12th centuries, rapid deterioration set in. The ground became permanently frozen about 1400 and the colonies disappeared.
The next centuries were generally rainy, but were chiefly remarkable for a readvance of glaciers all over the world; this period became known as the Little Ice Age. The glaciers began to expand during the 13th century. Their advance was slow at first and probably stopped completely during the second half of the 16th century, but it became very rapid from about 1600 to 1650. In Sweden the latter date marks one of the two points of greatest extension and was followed by a slight retreat, but in the Alps and Iceland it was little more than a temporary halt. The second maximum occurred at or a little before 1750, when the glaciers reached an extension greater than at any other time since the end of the Quaternary Ice Age. Since then there has been a general retreat, slow at first and broken by a halt or readvance anout 1850, but again becoming rapid during the 20th century.
Instrumental observations began in England in 1677, when there was a period of dry continental climate. About 1750 this changed to a more oceanic climate, with mild winters and cool rainy summers. There was a brief return of the continental type from 1794 to 1810, with prevailing easterly winds and a notable period of severe winters. After 1850 winters became progressively warmer in nearly all polar and temperate regions, but the colder winters beginning about mid-20th century may indicate a reversal of this tendency.
The broad pattern of climatic change since the end of the Ice Age is consistent with the hypothesis of an alternate weakening and strengthening of the planetary atmospheric circulation, associated with alternate poleward and equatorward shifts of the wind zones. At times of minimum circulation the circumpolar belt of west winds contracts and anticyclones are frequent in middle latitudes. Winds are variable, rainfall is small and the climate continental, with cold winters and hot summers. When the circulation is stronger, westerly winds predominate, storms are more frequent and penetrate into lower latitudes, the rainfall is heavier and climate more oceanic. This, with a few short interludes, was the general condition during the Sub-Atlantic and after about A.D. 1200.
New York Times
Tuesday, January 17, 2012
The current issue of the journal Science contains a proposal to slow global warming that is extraordinary for a couple reasons:
- 1. In theory, it would help people living in poor countries now, instead of mainly benefiting their descendants.
- 2. In practice, it might actually work.
This proposal comes from an international team of researchers- in climate modeling, atmospheric chemistry, economics, agriculture and public health- who started off with a question that borders on heresy in some green circles: Could something be done about global warming besides forcing everyone around the world to use less fossil fuel?
Ever since the Kyoto Protocol imposed restrictions in industrial countries, the first priority of environmentalists has been to further limit the emission of carbon dioxide. Burning fewer fossil fuels is the most obvious way to counteract the greenhouse effect, and the notion has always had a wonderfully virtuous political appeal- as long as it’s being done by someone else.
But as soon as people are asked to do it themselves, they follow a principle identified by Roger Pielke Jr. in his book “The Climate Fix.” Dr. Pielke, a political scientist at the University of Colorado, calls it iron law of climate policy: When there’s a conflict between policies promoting economic growth and policies restricting carbon dioxide, economic growth wins every time.
The law holds even in most ecologically correct countries of Europe, as Dr. Pielke found by looking at carbon reductions from 1990 until 2010.
The Kyoto Protocol was supposed to put Europe on a new energy path, but it contained so many loopholes that the rate of “decarbonization” in Europe did not improve in the years after 1998, when the protocol was signed, or after 2002, when it was ratified. In fact, Europe’s economy became more carbon-intensive in 2010, he says- a trend that seems likely to continue as nuclear power plants are shut down in Germany and replaced by coal-burning ones.
“People will make trade-offs, but the one thing that won’t be traded off is keeping the lights on at reasonable cost,” he says. Given the reluctance of affluent Europeans to make sacrifices, what are the odds of persuading billions of people in poorer countries to pay more for energy today in return for a cooler climate at the end of the century?
But suppose they were offered a deal with immediate benefits, like the one proposed in Science by researchers in the United States, Britain, Italy, Austria, Thailand, and Kenya. The team looked at ways to slow global warming while also reducing the soot and smog that are damaging agriculture and health.
Black carbon, the technical term for the soot spewed from diesel engines and traditional cookstoves and kilns, has been blamed for a significant portion of the recent warming in the Arctic and for shrinking glaciers in the Himalayas. Snow ordinarily reflects the sun’s rays, but when the white landscape is covered with soot, the darker surface absorbs heat instead.
Methane, which is released from farms, landfills, coal mines, and petroleum operations, contributes to ground-level ozone associated with smog and poorer yields from crops. It’s also a greenhouse gas that, pound for pound, is far more powerful than carbon dioxide at trapping the sun’s heat.
After looking at hundreds of ways to control these pollutants, the researchers determined the 14 most effective measures for reducing climate change, like encouraging a switch to cleaner diesel engines and cookstoves, building more efficient kilns and coke ovens, capturing methane at landfills and oil wells, and reducing methane emissions, from rice paddies by draining them more often.
If these strategies became wide-spread, the researchers calculate, the amount of global warming in 2050 would be reduced by about one degree Fahrenheit, roughly a third of the warming projected if nothing is done. This impact on temperatures in 2050 would be significantly larger than the projected measures for reducing carbon dioxide emissions.
Not incidentally, the researchers calculate, these reductions in low-level ozone and black carbon would yield lots of benefits long before 2050. Because people would be breathing cleaner air, 700,000 to 4.7 million premature deaths would be avoided each year. Thanks to improved crop yields, farmers would produce at least 30 million more metric tons of food annually.
“The beauty of these pollution-control measures is that over five to ten years they pay for themselves in the developing world,” says Drew Shindell, the lead author of the proposal, who is a climate scientist at the NASA Goddard Institute for Space Studies and at Columbia University. “They slow global warming, but there are local benefits too. If you make black carbon reductions in China or India, you get most of the benefits in China or India.”
These ideas already have a few fans, including Ted Nordhaus, a founder of the Breakthrough Institute, which has endorsed similar measures in a report called “Climate Pragmatism.” Mr. Nordhaus sees the Science paper as a model for the future.
“This is what the post-Kyoto world will look like,” he says. “We’ll increasingly be managing ecological problems like global warming, not solving them. We may make some headway in limiting our emissions, but if we do so it will be through innovating better energy technologies and implementing them at the national and regional level, not through top-down international limits.”
These pollution-control policies aren’t especially controversial- even Republicans hostile to environmentalists have supported research into black carbon- but neither have they been especially popular. Mainstream environmental groups haven’t put them on the agenda. One reason is the lack of glamour: Encouraging villagers to use diesel engine filters and drain their rice paddies is less newsworthy than negotiating a global treaty on carbon at a United Nations conference.
Another reason is the fear of distracting people from the campaign against carbon dioxide, the gas with the most long-term impact. Because it lingers in the atmosphere much longer than soot or methane, some scientists argue that it must be the first step. Dr. Shindell says he agrees with the need to limit carbon dioxide and sympathizes with those who worry about losing focus.
“But I also worry that carbon dioxide will go up even if we do focus on it,” he says. “We’re at a complete deadlock on carbon dioxide. Dealing with the short-lived polutants might really be a way to bridge some of the differences, both between the two sides in the United States and between the developed and the developing world.”
No matter what people think about global warming, there aren’t a lot of fans of dirty snow, poor crops, and diseased lungs.