Global Warming - Greenhouse Effect - Part 3

1990s hottest decade of millennium, report shows

Reuters - Washington - March 10, 1999

The 1990s were the warmest decade of the millennium, with 1998 the warmest year so far, researchers said Wednesday. The study adds to a growing body of evidence that the global climate has been getting steadily warmer, especially the last half of the 20th century.

"Temperatures in the latter half of the 20th century were unprecedented," Raymond Bradley of the University of Massachusetts said in a statement.

Their report, published in Geophysical Research Letters, shows that temperatures dropped an average of 0.02 degrees C (0.04 degree F) per century for the 900 years before the 20th century.

Because human climate records only go back a few hundred years, and do not cover the whole globe, the team at the University of Massachusetts and the University of Arizona looked at measurements other scientists have made of tree rings, ice cores and other "proxy indicators" that record climate variations.

They heavily relied on three sets of 1,000-year-long tree-ring records from North America, as well as tree rings from northern Scandinavia, northern Russia, Tasmania, Argentina, Morocco, and France.

The ice cores they studied came from Greenland and the Andes mountains in South America.

"As you go back farther in time, the data become sketchier," Michael Mann of the University of Massachusetts said. "One can't quite pin things down as well, but our results do reveal that significant changes have occurred, and temperatures in the latter 20th century have been exceptionally warm compared to the preceding 900 years."

He said the records were not perfect, but complete enough to show "startling revelations." "If temperatures change slowly, society and the environment have time to adjust," he said. "The slow, moderate, long-term cooling trend that we found makes the abrupt warming of the late 20th-century even more dramatic.

"The cooling trend of over 900 years was dramatically reversed in less than a century. The abruptness of the recent warming is key, and it is a potential cause for concern."

In January the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) said they had established that 1998 was the warmest year on record. But their finding was based on records only going back 120 years.

In January the American Geophysical Union, which publishes Geophysical Research Letters, called for continued efforts to curb human-made carbon emissions to stop global warming.

In December the World Meteorological Organization (WMO) said the earth's mean surface temperature in 1998 was 0.58 degrees C above the average for the benchmark period 1961-90. For the century, global temperatures were almost 0.7 degrees C above those at the end of the 19th century.

A warmer global climate melts the ice caps, raising sea levels, and disturbs weather patterns, causing droughts, severe storms, tornadoes, hurricanes and blizzards.

Globe's average temperature this year highest since records kept in 1860

Geneva -December 17, 1998--AP

The average temperature around the globe this year will be the highest since comprehensive records were first kept in 1860, the World Meteorological Organization said on Thursday. In its annual statement on the global climate, the United Nations agency said the earth's mean surface temperature in 1998 would be 0.58 degrees Centigrade above the average for the benchmark period 1961-90. At the end of last year, the previous warmest, the temperature was 0.43 degrees Centigrade above the average. As the 21st century approaches, the WMO said, global temperatures were almost 0.7 degrees Centigrade above those at the end of the 19th century.

The WMO said its calculations were based on readings from stations in most countries around the world. It declines to give an absolute average global temperature, saying this would be meaningless. 1998 would be the 20th consecutive year in which global surface temperatures were above normal, the statement added. The 10 warmest years have all been since 1983, and seven of them since 1990, the WMO said. Up to the end of October, new monthly temperature records had been set in each of the previous 18 months.

Regional patterns this year from January to the end of November showed all continents returning above average temperatures, except for the northern sections of Eurasia. In a comment on the findings, WMO Secretary-General Godwin Obasi said they showed that the international community should maximize efforts to fight global warming.

History of Global Warming

Washington- -December 17, 1998 --Nando

Arctic temperatures were warmer in the Late Cretaceous period, some 92 to 86 million years ago, than scientists first thought, according to a study in Science magazine to be published Friday. Vertebrate fossils, including those of the crocodile's ancestors, the champosaurs, a reptile that could not have survived below freezing temperatures, were found in the Canadian Arctic, the study said. According to professor J. Tarduno, one of the study's authors, the presence of these fossils proves the region had an average annual temperature of 14 degrees Celcius (57 Fahrenheit). The temperate climate was caused by an increase of carbon gas in the atmosphere from volcanic eruptions around the world, Tarduno said.

Analysis of ice cores suggests global climate change occurred 12,500 years ago

Washington--October 2, 1998

The top and the bottom of the Earth turned sharply warmer at the same time 12,500 years ago, suggesting that a major climate change once thought to be regional may have affected the entire planet during that time period. Climate temperatures climbed by more than 20 degrees, enough to melt sea ice and end the planet's last major ice age.

James White, a climatologist at the University of Colorado, Boulder, said that an analysis of new ice cores from the Antarctica show that the south polar area went through a rapid temperature increase at the same time the north polar region was warming. White, co-author of the study, said that the Antarctica ice cores show a temperature increase of about 20 degrees Fahrenheit within a very short time.

Ice cores from Greenland, near the Arctic, show that at the same time there was a temperature increase of almost 59 degrees in the north polar region within a 50-year period, White said. "What we see in Antarctica looks very, very similar to what we see in Greenland," said White. "We used to suspect that some of these big changes that occurred naturally in the past were only local. Since we see the same thing at opposite ends of the Earth, it does imply that the warming was a global phenomena."

He said the findings "throw a monkey wrench into paleo-climate research and rearrange our thinking about climate change at that time." White said researchers need to look more closely at how the Earth's climate slipped from an ice age that ended about 12,500 years ago and shifted into the current, more temperate climate. The findings, he said, also increase the urgency for researchers to understand climate shifts because it appears they could be abrupt and happen all over the Earth at the roughly the same time.

The warming 12,500 years ago came within a typical human lifetime. Such rapid shifts in the climate on a global basis would make it very difficult for humans to adjust, he said. Climate affects agriculture, energy use, transportation and population shifts, and rapid changes would make adjustment in these areas more difficult. White said the Antarctica ice cores also showed that there was a sudden rise in methane, a major greenhouse gas. Methane, carbon dioxide and some other gases can accumulate in the atmosphere and trap heat from the sun, causing a general warming.

Many scientists now believe that the Earth's climate may be warming because the burning of fossil fuels and other human processes have increased the amount of greenhouse gases in the atmosphere. White said that global warming caused by man-made greenhouse gases may be similar to warming that may occur naturally. "What humans are doing is in a way no different than what natural systems do," he said. "Humans add methane to the atmosphere. So does nature. We are simply doing it faster."

For this reason, said White, studying natural climate change of the past may give a fundamental understanding of how human actions could change the climate in the future.

Thomas F. Stocker of the Physics Institute at the University of Bern, Switzerland, said the research reported by White and his colleagues is surprising. Stocker wrote in Science that the study suggests warming in Antarctica "may be synchronous with the well-documented abrupt warming 12,500 years ago in the Northern Hemisphere." Stocker said more analysis of White's ice core and a comparison with ice cores obtained elsewhere in Antarctica "are required to get a clearer picture" of the south polar climate change. White said that the warming trend detected in his ice core taken from a seaside drill site was not found in ice cores taken from Antarctica drill sites that were farther inland.

September 25, 1998 -- The rate that North America's largest masses of ice are thawing is raising concerns that some glaciers could disappear entirely within a century. Photos taken during the past several decades clearly document that global warming is causing a dramatic reduction in size of some of the continent's best-known glaciers. Even Glacier National Park, in the northern Rocky Mountains, could be without its namesake in 50-70 years if the current trend continues.

The trend is especially evident in Alaska, where the Columbia Glacier retreated 8 miles (13 km) during the past 16 years. The glacier forms a river of slowly moving ice that used to flow into Prince William Sound in the Gulf of Alaska. While temperatures around the world have risen less than one degree Celsius on average this century, they have risen twice as much in glacial regions like Alaska, where the winters are most noticeably warmer. The rising temperatures are also affecting high-latitude forests: The mountains flanking the Columbia Glacier are now full of dead or dying trees.

Future Effects of Global Warming Not Known

September 17, 1998

Washington (Reuters) - Science is not close to understanding the future effects of global warming, according to researchers Tuesday who urged a better system for predicting long-term climate change.

Otherwise, according to a report by the National Research Council, floods, storms and droughts will continue to devastate agriculture, kill people and destroy property.

The report, put together by nationwide teams of experts, found that climate was changing and would continue to do so with or without human influences.

``In 1992 and 1993 ice cores approximately 1.8 miles long were extracted from the heart of the Greenland ice sheet, revealing changes in the Earth's climate system over the last 150,000 years or so,'' the report said.

``One of the most remarkable revelations of these cores was the fact that the climate in the Holocene (the past 10,000 years) -- a period that we might consider representative of our modern climate conditions -- has undergone considerable natural variation.''

In modern times, much milder extremes have had huge effects -- such as the ``devastating'' floods in the U.S. Midwest in 1993 and 1997, the research said.

Then there is global warming, which most experts agree is partly caused by humans who burn fossil fuels, cut down forests and release chemicals into the atmosphere, according to the report.

The study, funded in part by the National Oceanic and Atmospheric Administration (NOAA), said researchers had been able to make some long-term predictions. For instance, experts know about El Nino, the Pacific current blamed for causing droughts, floods and other weather disruptions every few years.

Rainfall in northwestern Europe and western North America can also be predicted months in advance, to some degree.

But making longer forecasts would be harder because of the complexities of climate change, the researchers said. The National Research Council is made up of three government institutes-- the National Academy of Sciences, the National Academy of Engineering and the Institute of Medicine.

Northern Hemisphere the Warmest in Past 600 Years

New York -April 23, 1998 (AP)

The years 1997, 1995 and 1990 were the warmest in the Northern Hemisphere since the days of Christopher Columbus, a study says. Researchers say they found evidence that rising levels of greenhouse gases are probably responsible.

Scientists reconstructed annual average temperatures back to the year 1400 andfound no year warmer than those three. Either 1997 or 1995 could be considered the warmest, depending on whether one considers temperatures over land or at the ocean surface or both, researcher Michael Mann said.

When land and ocean temperatures are combined, 1997 and 1995 ran about nine-tenths of a degree Fahrenheit above the average for the 20th century. Climate experts said that the study is an early step in such long-term reconstructions and that more work is needed to improve them, but that the finding about the warmest years fits in with previous studies.

Last January, the government announced that 1997 was the warmest year globally in about 100 years, which was as far back as the researchers checked.

To reconstruct temperatures over the past 600 years, Mann and colleagues used a network of indirect indicators, including ancient tree rings, coral and ice as well as historical records. They compared these indicators to actual temperature measurements from 1902 to 1980 to find how to use the ancient data to estimate average annual temperatures.

They also looked at trends in three influences on climate: variations in the sun's brightness, volcanic activity and the atmosphere's supply of carbon dioxide, a heat-trapping greenhouse gas. They looked for statistical relationships that would suggest which was influencing the hemisphere's climate.

While the sun's brightness and volcanoes appeared important in the past, greenhouse gases appear to dominate over the past few decades.