A new study, led by James Hansen of NASA and published on-line today (September 25) in the Proceedings of the National Academy of Sciences, concludes that, because of a rapid global warming trend over the past 30 years, Earth is now reaching and passing through its warmest level in nearly 12,000 years—since the end of the last ice age. The most important result found by the study 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. According to Hansen, “That means that further global warming of 1 degree Celsius defines a critical level.”
Excerpt from the NASA GISS release:
NASA Study Finds World Warmth Edging Ancient Levels
Sep. 25, 2006
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.
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 0.36 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….
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 (1.8F) 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.”
Global warming is already beginning to have noticeable effects in nature. Plants and animals can survive only within certain climatic zones, so with the warming of recent decades many of them are beginning to migrate poleward. A study that appeared in Nature Magazine in 2003 found that 1700 plant, animal and insect species moved poleward at an average rate of 6 kilometers (about 4 miles) per decade in the last half of the 20th century.
That migration rate is not fast enough to keep up with the current rate of movement of a given temperature zone, which has reached about 40 kilometers (about 25 miles) per decade in the period 1975 to 2005. “Rapid movement of climatic zones is going to be another stress on wildlife,” according to Hansen. “It adds to the stress of habitat loss due to human developments. If we do not slow down the rate of global warming, many species are likely to become extinct. In effect we are pushing them off the planet.”
An Associated Press story—“Global Temperature Highest in Millennia”—published in the New York Times on-line, reporting this study.
Abstract of the article published online before print September 25, 2006
One section of the article is on “Estimating Dangerous Climate Change,” with sub-sections on modern vs. paleo temperatures, criteria for dangerous warming, and a discussion of implications. This material will probably be rather tough going for most general readers, but it exemplifies the discourse that is going on among leading climate scientists.