Virtually tying 1998 as the hottest year on record, 2005 continued a warming trend that has increased rapidly in recent decades and offered more evidence that the planet is experiencing a dramatic climate shift.
Four separate temperature analyses released Thursday varied by a few hundredths of a degree but agreed it was either the hottest or second-hottest year since the start of record-keeping in the late 1880s. Unlike 1998, however, 2005 had no El Nino -- a natural weather phenomenon -- to warm ocean waters, which affects temperatures worldwide.
The planet has been slowly warming for a century, and the 10 hottest years on record have all occurred since 1990, a trend that a majority of scientists say is in large part attributable to human production of greenhouse gases, which trap heat in the atmosphere.
“The last 10 years have been exceptionally warm,” said Raymond Bradley, a climate scientist at the University of Massachusetts in Amherst. “2005 continues this extraordinary sequence of warm temperatures.”
This year saw above-average temperatures across the majority of the planet, with extreme warmth in the high latitudes of the northern hemisphere, including Alaska, Russia and Scandinavia, said Jay Lawrimore, chief of the climate monitoring branch of the National Oceanic and Atmospheric Administration.
A minority of scientists dispute the findings and say the measurements used to take the planet’s temperature are spotty, inaccurate and may exaggerate the amount of warming.
“We’re asking too much of the data,” said Roger A. Pielke Sr., Colorado’s state climatologist.
According to scientists at NOAA, a preliminary ranking shows that 2005 was 1.06 degrees warmer than the long-term average of 57 degrees, and 1998 was 1.12 degrees warmer. When final numbers for 2005 and an improved analysis system are used early next year, 2005 is likely to end up being ranked as the hottest year, Lawrimore said.
A NASA analysis showed 2005 to be the hottest year, while analyses by the United Nations World Meteorological Organization and the U.K.'s climate authority, the Hadley Centre, showed 2005 to be a close second to 1998. The groups use the same temperature data but differ in how they analyze them, particularly in remote areas such as the Arctic, where there are few thermometers. The numbers also vary because the groups use different adjustments to remove the “urban heat island effect,” which causes warmer temperatures in areas with large amounts of pavement, buildings, people and cars.
Despite these differences, the numbers end up being so close that all groups said it was nearly impossible to distinguish 2005 temperatures from those in 1998.
“We’re somewhat surprised by how similar [the analyses] are,” Lawrimore said.
Much of the warming in 1998 was a result of the so-called “El Nino of the century,” which contributed about a third of the planet’s excess warmth. The fact that 2005, a year with a negligible El Nino effect, saw temperatures that rivaled those of 1998 is clear evidence of an “intense underlying global warming trend,” said James Hansen, who compiles temperature data at the NASA Goddard Institute for Space Studies in New York.
“If you look at a time series, ’98 just stands out so dramatically. Then you look at the past several years and you see it creeping back up. It’s quite striking,” Lawrimore said.
The new data on warming temperatures come amid other manifestations of a changing climate, including a record loss of sea ice in the Arctic this summer.
“The sea ice was a record minimum in the satellite era since 1979 and probably in the last century,” said Mark Serreze, a senior researcher at the National Snow and Ice Data Center at the University of Colorado. “Compared to where it should have been, you’ve lost an area roughly twice the size of Texas.”
Serreze said the Arctic is on track to be ice-free in summer by 2070. “What you’re starting to see is the greenhouse effect starting to emerge,” he said.
Scientists with the U.S. Minerals Management Service this week reported the apparent drowning of four polar bears in 2004, observed during agency flights over the Beaufort Sea. Scientists said they spotted an “unusually large” number of bears swimming farther offshore than usual, and subsequently saw floating polar bear carcasses. It concluded that drownings would probably increase as sea ice continued to diminish.
Three environmental groups Thursday sued the U.S. government, demanding threatened status for the polar bear under the Endangered Species Act, contending that the bears are victims of global warming. The bears’ native habitat is shrinking as sea ice levels diminish, and human activities such as burning fossil fuels are to blame, the groups contend.
“Their sea-ice habitat, their hunting ground, is literally melting away,” said Kassie Siegel of the Center for Biological Diversity, which had petitioned the government to consider listing the bear earlier this year.
Last month, Papua New Guinea announced that it would begin evacuating the 980 residents of the Carteret atolls to Bougainville Island because of rising sea levels linked to global warming. The atolls, barely above sea level, are expected to be completely submerged by 2015.
A number of climate scientists said the steady march of warm temperatures, along with retreating sea ice, melting glaciers and rising sea levels, were clear evidence that global warming caused by the human production of greenhouse gases was already dramatically affecting the planet.
“Could these changes arise from natural climate variability alone? The answer is no,” said Ben Santer, a physicist and climate modeler at the Lawrence Livermore National Laboratory. “Even today, one can hear statements -- sometimes from senior members of our government -- saying we know nothing about the causes and effects of climate change. That’s really not true.”
Angela Ledford Anderson, director of the environmental coalition Clear the Air, called for the U.S. Senate to create “mandatory pollution limits with clear deadlines” to curb the chemicals that are causing warming.
Bush administration officials said Thursday that they were taking climate change seriously by launching an array of voluntary programs to reduce greenhouse gases and investing nearly $2 billion to monitor and study climate change. At the same time, administration officials downplayed the 2005 temperature data, saying it remained unclear how much human activities had contributed to the warming trend.
“The observed conditions of any one particular year are a combination of natural and human-related factors,” said Michele St. Martin, a spokeswoman for the White House Council on Environmental Quality.
Pielke, who directs the Colorado Climate Center at Colorado State University, doubts the accuracy of global temperature estimates because some temperature monitors record extra warmth when placed too close to buildings and because they do not measure humidity, which is an important factor in gauging heat.
“This raises issues about the validity of this data,” he said, adding that he does believe the planet is warming, but not as quickly as global temperatures suggest.
Scientists expect global temperatures to continue rising. Hansen had predicted in a report issued in February that 2005 temperatures could rival or exceed those of 1998 because the Earth is “out of energy balance” and is absorbing more heat from solar radiation than it is radiating out to space.
He now predicts that the 2005 and 1998 records will soon be broken.