By Robert Hazen, Ph.D., George Mason University
The Earth’s climate seldom changes much on human time scales, but there’s new evidence that suggests that the Earth may occasionally experience short periods of dramatic climate change. By some estimates, we are now in the middle of such a period of rapid global warming. In recent years, it seems that the Earth is getting warmer at an alarming rate, perhaps several degrees per century.
Problems of Measuring Global Temperature
The average global temperature is extremely difficult to measure, but the 15 hottest years on record have all occurred since 1980; 1998, the most recent year that’s been surveyed at this point, is by far the hottest year since records began being kept in the 1870s; it was a quarter of a degree warmer than any previous year.
Long-term sites of weather stations have become more urbanized, and so one has to worry about things like heat-island effects. As one urbanizes a weather station—more and more concrete, more and more asphalt—the area tends to get warmer; it just absorbs more of the Sun’s heat.
However, there are other ways to get around this: one can make satellite measurements of global temperature; they can measure the average temperature of the water from satellites, and so forth. While these measurements are difficult, it now seems to genuinely indicate that the globe is getting warmer, by all different measurements.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Future of the Earth’s Climate
By the most optimistic estimates, the global average temperature is going to rise at least two degrees centigrade by the year 2100, and there are other estimates that are at least three times that. Such a climate change would induce a significant increase in sea level.
It would cause a shift in agricultural lands much farther to the north. Some of the fertile areas in the Midwest would become dry and difficult to farm, whereas there are new areas in Canada that would suddenly open up as agricultural areas.
Whatever the cause, we have to learn more about the factors that affect climate, and an important new scientific discipline in this regard is called paleoclimatology.
Learn more about the Earth as a planet.
Studying the Past to Predict the Future
Paleoclimatology is the study of ancient climates, which are revealed by a whole variety of evidence. One can, for example, look to fossils; fossil plants and animals provide essential clues.
Fossil pollen grains, for example, reveal the distribution of plants, and the kinds of species, the ones with distinctive habitats. Fossil corals can indicate the regions where there were coral reefs and warm water. One can also look at rock types. Glacial deposits, for example, indicate that there was glaciation and ice ages in a region.
One of the neat ways that people do paleoclimatology is through ice cores. One can get ice cores in Greenland and Antarctica, and some of these hold a continuous record of more than 100,000 years, year-by-year records of ice deposition; and they hold records of the atmosphere in the concentration of tiny air bubbles that are encased in the ice.
It turns out that one can determine air temperature from these air bubbles because of the ratio of the lighter oxygen-16 isotope to the heavier oxygen-18 isotope. That’s a very sensitive indicator of temperature. The warmer it is, the easier it is for the heavier oxygen-18 to enter the atmosphere, and so a high O18 value gives us a higher average global temperature of the atmosphere.
Sudden Climate Change Has Happened in the Past
The ice-core climate record seems to indicate that dramatic temperature changes can take place in very short periods of time. Both in Greenland and in Antarctica, there are places where there was a 10-20 degrees centigrade temperature change in just a few decades; for example, at the end of the glacial advance, about 12,500 years ago.
Some scientists suggest that this event was caused by a rapid rise in greenhouse gases, perhaps released from the ocean. Carbon dioxide from volcanoes is another possibility; or methane, which is also sometimes trapped in the pockets in the ocean floor.
The fact is, we don’t know what has caused the drastic, sudden climate changes, but we do know that a similar rapid warming today could have catastrophic effects on the world’s ports that are near sea level, on agriculture, and on many other aspects of civilization that we take for granted.
Learn more about volcanoes.
Factors that Affect Climate Change
One of the most intriguing aspects of climate studies is a growing realization that there’s a strong link between climate and plate tectonic processes. The climate of a region is profoundly affected by details of the distribution of landforms and bodies of water. For example, one can have an ocean current that takes warm water from equatorial regions to areas where it’s much, much colder.
A mountain range can cause intense changes in climate as well. One can have some regions that are extremely dry because the mountains block the passage of wet air; other areas that are extremely wet because a mountain is in the way and intercepts wet air masses. Even the position of continents, and whether there’s a continent on a pole, determines much about the climate of the globe.
Some fascinating changes in climate are also the result of currents. For example, the California current, which takes cooler air from the Bering Sea area down along the California coast, moderates the climate of California in quite a dramatic way.
Common Questions about the Rapid and Dramatic Changes in the Earth’s Climate
All the measurements indicate that the globe is getting warmer. By the most optimistic estimates, the global average temperature is going to rise at least two degrees centigrade by the year 2100.
Paleoclimatology is the study of ancient climates, which are revealed by a whole variety of evidence. The field uses fossils of plants and animals as well as other evidence to advance its findings.
The climate of a region is profoundly affected by details of the distribution of landforms and bodies of water. There’s also a strong link between climate and plate tectonic processes.