DISCIPLINE BY DISCIPLINE:
Weather is an extremely complicated phenomenon, reflecting a slew of interrelated factors. In 2001, several studies were reported that identified a role for yet another factor: dust. More than 2000 tons of dust are blown into the air each year. Although some settles down near its source of origin, dust from such places as North Africa and the deserts of western China is routinely picked up by strong, high winds and reaches halfway around the world. Roughly half the dust in the atmosphere is produced by natural forces, and half is produced by agricultural and other human activities, according to a study by researchers at the University of Michigan at Ann Arbor that was published in August 2001.
Dust is hard for meteorologists to study because there are many different types of dust. Light dust can cool Earth by preventing sunlight from reaching the ground, but dark dust absorbs sunlight and warms the atmosphere. In addition, dust is a periodic event. A wind storm can launch large quantities of dust into the atmosphere for weeks at a time, but then the dust settles out and the atmosphere clears again. Nonetheless, scientists are trying to sort out dust’s impact on climate change. A study of dust from North Africa, published by researchers from the University of Miami in August 2001, found that overall dust has had a slight cooling effect on Earth. But scientists note that dust from North Africa tends to be light and reflective, so researchers are attempting to collect dust from more sources worldwide.
One of the mysteries about the history of Earth’s climate is that at times, the climate across the globe changes rapidly. An example of this is the Younger Dryas event, which took place about 11,500 years ago. Earth was emerging from the last ice age, and global temperatures were warming. Suddenly, global temperatures dropped again and stayed low for centuries, extending the ice age significantly
Scientists have theorized that when the ice sheets began to melt in the northern hemisphere, the influx of fresh water shut down water circulation in the North Atlantic Ocean, cooling the region and Earth as a whole. However, in a paper that appeared in the June 1, 2001, issue of the Journal of Climate, a group of scientists from the Lamont-Doherty Earth Observatory in Palisades, New York, suggested a new theory linking sudden climate change to the interactions between the ocean and atmosphere that give rise to the El Niño event in the Pacific Ocean.
El Niño is a mass of warm water that appears on the surface of the eastern equatorial Pacific Ocean. El Niños usually occur about every four to seven years and last between 14 and 22 months, strongly affecting weather worldwide. The Lamont-Doherty scientists theorize that gradual changes in the shape of Earth’s orbit around the Sun, as well as the tilt of its axis, can cause El Niños to disappear for centuries at a time. The absence of El Niños, the scientists said, could cause global temperatures to drop considerably. Although the link between El Niño and rapid climate change remains speculative, the scientists note that the disappearance of El Niños can be quite abrupt, and the impact of the event on global weather is known to be profound.