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Last 50 years 'unusually warm', tropical glaciers melting rapidly finds research

June 27, 2006

Researchers studying ancient tropical ice cores have found evidence of two abrupt climate shifts -- one 5000 years ago and one currently underway. The findings, published in the current issue of the journal Proceedings of the National Academy of Science, may have important implications for immediate future since more than two-thirds of the world's population resides in the tropics.

Using chronological climate records retrieved from seven locations in the South American Andes and the Asian Himalayas, researchers from Ohio State University's Byrd Polar Research Center, the University of Texas; the University of Connecticut, and the University of Louisville found evidence that a massive climate shift to a cooler regime occurred just over 5,000 years ago, followed by a rapid reversal to much warmer temperatures in the last 50 years.

The scientists also say that most of the high-altitude glaciers in the planet's tropical regions are rapidly melting and will likely disappear in the near future. Glaciers and ice caps are retreating even in areas where precipitation is increasing suggesting that increasing temperatures and not decreasing precipitation as the most likely culprit behind the decline.

The researchers' records show that the past 50 years have been unusually warm.

"There hasn't been anything in the record like it – not even the [Medieval Warm Period 700 to 1000 years ago] ," said Lonnie Thompson, professor of geological sciences at Ohio State. "The fact that the isotope values in the last 50 years have been so unusual means that things are dramatically changing. That's the real story here."

Further, the emergence of 5,000 to 6,500 year old wetland plants around the margin of the Quelccaya ice cap in Peru, suggests that temperatures there are higher than any time in the past 5000 years.

Thompson says the research has important implications for global climate and human populations.

"Tropical glaciers are the ‘canaries in the coal mine' for our global climate system, as they integrate and respond to most of the key climatological variables – temperature, precipitation, cloudiness, humidity and radiation," he explained. "The uniformity of the climate in the tropics makes these kinds of records so critical since they tell us what is happening to global temperatures."

“What this is really telling us is that our climate system is sensitive, it can change abruptly due to either natural or to human forces,” he continued. “If what happened 5,000 years ago were to happen today, it would have far-reaching social and economic implications for the entire planet.

“The take-home message is that global climate can change abruptly, and with 6.5 billion people inhabiting the planet, that's serious.”

“Approximately 70 percent of the world's population now lives in the tropics so when climate changes there, the impacts are likely to be enormous,” said Thompson.

Africa's glaciers gone by 2025. Fabled equatorial icecaps will disappear within two decades, because of global warming, a study British and Ugandan scientists has found. In a paper to be published 17 May in Geophysical Research Letters, they report results from the first survey in a decade of glaciers in the Rwenzori Mountains of East Africa. An increase in air temperature over the last four decades has contributed to a substantial reduction in glacial cover, they say.

China's glaciers shrinking by 7 percent per year. The glaciers of China's Qinghai-Tibet plateau are shrinking by 7 percent a year due to global warming according to a report from Xinhua, the state news agency of China.

Earth at Warmest in 400 Years. There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other proxies of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years, according to a new report from the National Research Council. Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600, said the committee that wrote the report, although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900. Very little confidence can be placed in statements about average global surface temperatures prior to A.D. 900 because the proxy data for that time frame are sparse, the committee added.

The tropics may be expanding due to climate change . A new study published in Science by scientists from the University of Utah and the University of Washington indicates that the tropics have expanded farther from the equator since 1979.Analyzing atmospheric temperature measurements by satellites, the researchers say that widening of the tropics amounts to 2 degrees of latitude or 140 miles but are not sure whether the expansion is the result of natural climate variation or by human-induced global warming due to the buildup of greenhouse gases in the atmosphere. The researchers warm that the trend could expand some of the world's driest regions.

Extreme global warming likely by end of century. Climate models predicting a 5.6 degrees Celsius increase in Earth's temperature by the end of the century may have underestimated the increase by as much as 2.3C according to researchers at the University of California at Berkeley.

2005 was the warmest year on record. A new study by NASA indicates that 2005 was the warmest year in at least a century, surpassing 1998. According to their data, the five warmest years over the last century have occurred since 1997: 2005, then 1998, 2002, 2003 and 2004. NASA also announced that over the past 30 years, the Earth has warmed by 0.6 degrees C or 1.08 degrees F, and 0.8 degrees C or 1.44 degrees F over the past 100 years. The NASA study follows two studies from the World Meteorological Organization (WMO) and the National Oceanic and Atmospheric Administration (NOAA) released last year that suggested 1998 was the warmest year. According to the NASA researchers, the primary difference among the conclusions is the inclusion of data from the Arctic in the NASA analysis. 2005 appears to have been unusually warm in the Arctic, resulting in significant loss in sea ice.

World temperatures highest in 1200 years. World temperatures are higher than in any period over the last 1,200 years, according to a study published in the current issue of Science. In reaching their conclusion, a research team from the University of East Anglia in Britain analyzed 14 sets of temperature records including data from rings, fossil shells, ice cores, temperature records, and historical documents from North America, Europe and East Asia.

Carbon dioxide level highest in 650,000 years. Carbon dioxide levels are now 27 percent higher than at any point in the last 650,000 years, according to research into Antarctic ice cores published on Thursday in Science. Analysis of carbon dioxide in the ancient Antarctic ice showed that at no point in the past 650,000 years did levels approach today's carbon dioxide concentrations of around 380 parts per million (ppm). The Intergovernmental Panel on Climate Change (IPCC) projects that atmospheric carbon dioxide levels could reach 450-550 ppm by 2050, possibly resulting in higher temperatures and rising sea levels. There is fear that climate change could create a class of environmental refugees displaced from their homes by rising oceans, increasingly catastrophic weather, and expanding deserts

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