Melting Arctic Ice Linked to Human Combustion of Oil and Gas
© Environment News Service (ENS) 1999
December 3, 1999
By Cat Lazaroff
GREENBELT, Maryland, December 3, 1999 (ENS) - Enormous swaths of Arctic sea ice are vanishing each year, and humans are the likely culprits, a team of scientists announced Thursday. Using ground based and satellite data, the researchers estimate there is a 98 percent chance that the melt is due, at least in part, to global warming caused by human activities.
For the first time, scientists placed space based observations of Arctic sea ice retreats into a much longer term context, and have examined the likelihood that the sea ice decreases are in part because of human caused climate change.
The results seem to support doomsayers' predictions that climate change is the reason for the melting of the Arctic ice. Most scientists agree that the climate warms as heat-trapping gases emitted by burning oil and gas accumulate in the upper atmosphere.
Sea ice is a sensitive indicator of climate change - if the global climate is warming, then the amount of permanent sea ice in the Arctic should decrease.
Satellite measurements and surface observations have shown that the area of Northern Hemisphere sea ice has, in fact, been decreasing for almost 50 years. Two reports in today’s issue of the journal "Science" published by the American Association for the Advancement of Science present new measurements and analyze changes in Arctic sea ice.
One team, led by Konstantin Vinnikov of the University of Maryland, used computer climate models to examine whether the decreases observed in the ice cover of the Arctic over the past few decades are the result primarily of natural climate changes or might also be influenced by human induced global warming, says study co-author Dr. Claire Parkinson, a National Air and Space Administration (NASA) climatologist at the Goddard Space Flight Center in Greenbelt.
Their model suggests that the probability of this change being caused by natural variability is less than two percent for the last 20 years. They predict the decreases will continue during the next century.
Vinnikov and Parkinson conclude that the decrease in Northern Hemisphere sea ice is probably a result of human driven global warming.
The team combined five separate data sets to measure sea ice retreats. Scientists used two independent computer climate models to simulate how much ice there would be without human added carbon dioxide in the atmosphere.
"Satellite data from November 1978 through March 1998 (19.4 years) reveal that the Arctic ice extent overall has shown a downward trend of 37,000 square kilometers per year, meaning a loss each year of an ice area well exceeding the combined areas of the states of Maryland and Delaware. The total loss over 19.4 years would be an area exceeding the size of Texas," said Parkinson.
Taking the long-range view, the team used a 5,000 year run in a global climate model of the National Oceanic and Atmospheric Administration’s (NOAA) Geophysical Fluid Dynamics Laboratory at Princeton University. They found the probability of getting a negative trend over 19.4 years as large as that found from the satellite data was less than two percent if no human caused emissions were factored in.
The team then examined outputs from computer simulations that include human created increases in greenhouse gas emissions that tend to warm the atmosphere, and increases of smoke and dust that tend to cool the atmosphere. This model shows atmospheric warming that much more nearly matches the actual observations of Arctic sea ice shrinkage.
Vinnikov says that the results suggest that melting Arctic sea ice is probably related to human induced global warming. "We only have satellite data for a relatively short period of time," says Parkinson. "It was interesting to be able to put the satellite data into a longer term context by using the model simulations."
The study was done by a team of meteorologists, physicists, and climatologists from the University of Maryland, Rutgers University, NOAA, the University of Illinois, NASA, the Hadley Center in Great Britain, and the Arctic and Antarctic Research Institute in Russia.
A second study also points to dramatic changes in Arctic sea ice. Research by a team from Norway and Russia measured the extent of the perennial Arctic sea ice pack, and found that this area of multiyear ice has decreased by more than twice as much as that of total sea ice.
This change in ice cover has been accompanied by a decrease in ice thickness. The Russian/Norwegian team says this suggests the heat and fresh water balances of the Arctic may be changing in significant ways.
The team, led by Ola Johannessen of the Geophysical Institute at the University of Bergen, Norway, used microwave satellite remote sensing data to measure changes in the composition of ice cover. They found a reduction of about 14 percent in the area of multiyear ice in winters from 1978 to 1998.
If this apparent transformation continues, the team predicts, it may lead to a markedly different ice regime in the Arctic, altering heat and mass exchanges as well as ocean stratification.
As "Science" writer Richard Kerr warns, also in today’s issue, "If global warming is at fault, the entire ice pack will eventually disappear, with drastic climate implications for the Northern Hemisphere."
More evidence of human caused global warming comes from a new comparison of climate in the past millennium with projected climate for the new millennium.
The New York based conservation organization Environmental Defense Fund (EDF) prepared charts from existing models of global temperature change, sea level rise, and concentrations of the greenhouse gas carbon dioxide. They show that fairly stable historic patterns are now beginning to change quickly.
EDF’s report, released Wednesday, reveals the rapid onset of global warming and the potential for unprecedented warming in the next thousand years.
Without action to cut greenhouse gas emissions, the climate of the coming millennium is projected to be much warmer than in the past. Global temperature may rise to 10 degrees Fahrenheit (F) above the recent average by 2200, in the worst case shown.
If action to lower fossil fuel emissions does not start until 2100, it could result in a six degree F temperature increase by 2200.
Immediate action to cut fossil fuel use, however, may result in a less threatening increase of no more than three degrees F in the coming millennium.
"Humanity is creating a new climate for the new millennium. Once this climate change occurs, there's no going back," said Dr. Michael Oppenheimer, EDF chief scientist. "Actions taken now to cut greenhouse gas pollution will determine if adjustment to future climate will be manageable or impossible."