NASA: World Warmth Edging Ancient Levels, Earth Getting Close To Dangerous Levels Of Human-Made Pollution

The world's temperature is reaching a level that has not been seen in thousands of years, according to a study announced on Sept. 25 by the National Aeronautics and Space Administration (NASA).

The study, led by James Hansen of NASA's Goddard Institute for Space Studies, N.Y., along with scientists from other organizations concludes that, because of a rapid warming trend over the past 30 years, Earth is now reaching and passing through the warmest levels in the current interglacial period, which has lasted nearly 12,000 years. An "interglacial period" is a time when the area of Earth covered by glaciers was similar or smaller than at the present time. Recent warming is forcing species of plants and animals to move toward the north and south poles.

The study used temperatures around the world taken during the last century. Scientists concluded that these data showed Earth has been warming at the remarkably rapid rate of approximately 0.36 degrees Fahrenheit (0.2 degrees Celsius) per decade for the past 30 years.

"This evidence implies that we are getting close to dangerous levels of human-made pollution," Hansen said. In recent decades, human-made greenhouse gases have become the largest climate change factor. Greenhouse gases trap heat in the Earth's atmosphere and warm the surface. Some greenhouse gases occur naturally while others are due to human activities.

The study notes that the world's warming is greatest at high latitudes of the Northern Hemisphere, and the warming is larger over land than over ocean areas. The enhanced warming at high latitudes is attributed to effects of ice and snow. As Earth warms, snow and ice melt, uncovering darker surfaces that absorb more sunlight and increase warming, a process called a positive feedback. Warming is less over ocean than over land because of the great heat capacity of the deep-mixing ocean, which causes warming to occur more slowly there.

Hansen and his colleagues in New York collaborated with David Lea and Martin Medina-Elizade of the University of California, Santa Barbara (UCSB) to obtain comparisons of recent temperatures with historical temperatures over the past million years. The California researchers obtained a record of tropical ocean surface temperatures from the magnesium content in the shells of microscopic sea surface animals, as recorded in ocean sediments.

One of the findings from this collaboration is that the Western Equatorial Pacific and Indian Oceans are now as warm as, or warmer than, at any prior time in the Holocene. The Holocene is the relatively warm period that has existed for almost 12,000 years, since the end of the last major ice age. The Western Pacific and Indian Oceans are important because, as these researchers show, temperature change in those areas is indicative of global temperature change. Therefore, by inference, the world as a whole is now as warm as, or warmer than, at any time in the Holocene.

According to Lea, "The Western Pacific is important for another reason, too: it is a major source of heat for the world's oceans and for the global atmosphere."

The researchers find that the Eastern Pacific Ocean has not shown an equal magnitude of warming. They explain the lesser warming in the East Pacific Ocean, near South America, as being due to the fact this region is kept cool by upwelling, rising of deeper colder water to shallower depths. The deep ocean layers have not yet been affected much by human-made warming.

Hansen and his colleagues suggest that the increased temperature difference between the Western and Eastern Pacific may boost the likelihood of strong El Niños, such as those of 1983 and 1998. An El Niño is an event that typically occurs every several years when the warm surface waters in the West Pacific slosh eastward toward South America, in the process altering weather patterns around the world.

The most important result found by these researchers is that the warming in recent decades has brought global temperature to a level within about one degree Celsius (1.8 degree Fahrenheit) of the maximum temperature of the past million years. According to Hansen, "That means that further global warming of 1 degree Celsius defines a critical level. If warming is kept less than that, effects of global warming may be relatively manageable. During the warmest interglacial periods the Earth was reasonably similar to today. But if further global warming reaches 2 or 3 degrees Celsius, we will likely see changes that make Earth a different planet than the one we know. The last time it was that warm was in the middle Pliocene, about three million years ago, when sea level was estimated to have been about 25 meters (80 feet) higher than today."

James Hansen: http://www.giss.nasa.gov/staff/jhansen.html

This article originally appeared in the 09/01/2006 issue of Environmental Protection.

comments powered by Disqus