NASA - National Aeronautics and Space Administration

A new study by NASA scientists finds that the world's temperature is reaching a level that has not been seen in thousands of years.

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, the 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 in the Earth's history 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.

Image right: Because of a rapid warming trend over the past 30 years, the Earth is now reaching and passing through the warmest levels seen in the last 12,000 years. This color-coded map shows average temperatures from 2001-2005 compared to a base period of temperatures from 1951-1980. Dark red indicates the greatest warming and purple indicates the greatest cooling.Click image to enlarge. Credit: NASA

The study used temperatures around the world taken during the last century. Scientists concluded that these data showed the Earth has been warming at the remarkably rapid rate of approximately .36° Fahrenheit (0.2° Celsius) per decade for the past 30 years.

"This evidence implies that we are getting close to dangerous levels of human-made pollution," said Hansen. 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, which include water vapor, carbon dioxide, methane, nitrous oxide, and ozone, occur naturally, while others are due to human activities.

Image left: Because of a rapid warming trend over the past 30 years, the Earth is now reaching and passing through the warmest levels seen in the last 12,000 years. This color-coded map shows a progression of changing global surface temperatures from 1880 to 2005, the warmest ranked year on record. Dark red indicates the greatest warming and dark blue indicates the greatest cooling. Click image to view animation. + High resolution image Credit: NASA

The study notes that the world's warming is greatest at high latitudes of the Northern Hemisphere, and it is larger over land than over ocean areas. The extra warming at high latitudes is because of effects of ice and snow. As the Earth warms, snow and ice melt, uncovering darker surfaces that absorb more sunlight and increase warming. Warming is less over ocean than over land because the deep ocean can absorb great amounts of heat, and because they are so big, they take longer to warm.

The Western Pacific Ocean, which is a major source of heat for the world ocean and atmosphere, has warmed in the past century. Meanwhile, the Eastern Pacific Ocean has not warmed, because cold water rises from the deep ocean in the Eastern Pacific, keeping the surface waters cooler.

Image left: Data from this study reveal that the Earth has been warming approximately 0.2 degrees Celsius (.36 Fahrenheit) per decade for the past 30 years. This rapid warming has brought global temperature to within about one degree Celsius 1.8 Degrees Fahrenheit) of the maximum estimated temperature during the past million years. Click image to enlarge. Credit: NASA

Hansen and his colleagues suggest that the increased temperature difference between the Western and Eastern Pacific may lead to the development 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° F) of the maximum temperature of the past million years, which they suggest is a sensible upper limit for additional global warming. “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.”

Image right: The "greenhouse effect" is the warming of climate that results when the atmosphere traps heat radiating from Earth toward space. Certain gases in the atmosphere resemble glass in a greenhouse, allowing sunlight to pass into the "greenhouse," but blocking Earth's heat from escaping into space. The gases that contribute to the greenhouse effect include water vapor, carbon dioxide (CO2 ), methane, nitrous oxides, and chlorofluorocarbons (CFCs). Credit: U.S. EPA

Global warming is already beginning to have noticeable effects in nature. Plants and animals can survive only within certain temperature ranges. In the northern hemisphere, with the warming of recent decades, many species are beginning to move toward the North Pole. A study that appeared in 2003 found that 1700 plant, animal and insect species moved poleward at an average rate of about 4 miles per decade in the last half of the 20th century.

Hansen said, “If we do not slow down the rate of global warming, many species are likely to become extinct. In effect we are pushing them [the plants and animals] off the planet.”

Image left: This study notes that the greatest warming is occurring at high latitudes of the Northern Hemisphere. Here, white, snow-covered terrain acts a giant reflector that bounces incoming solar radiation back into space. As the snow cover melts, the percentage of sunlight reflected, or “albedo,” decreases. Instead, the darker ocean and exposed ground can absorb the light and heat-up, thus adding more energy for continued melting. Click image to view animation. Credit: NASA






Related Links:

+ NOAA Pacific Marine Environmental Laboratory El Niño page
+ NASA's Climate Change Resource Reel

 

 

Rob Gutro
Goddard Space Flight Center