A new study shows the Arctic climate system may be more
sensitive to greenhouse warming than previously thought, and
that current levels of Earth's atmospheric carbon dioxide may be
high enough to bring about significant, irreversible shifts in
Arctic ecosystems. Led by the University of Colorado at Boulder,
the international study indicated that while the mean annual
temperature on Ellesmere Island in the High Arctic during the
Pliocene Epoch 2.6 to 5.3 million years ago was about 34 degrees
Fahrenheit, or 19 degrees Celsius, warmer than today, CO2 levels
were only slightly higher than present. The vast majority of
climate scientists agree Earth is warming due to increased
concentrations of heat-trapping atmospheric gases generated
primarily by human activities like fossil fuel burning and
deforestation. The team used three independent methods of
measuring the Pliocene temperatures on Ellesmere Island in
Canada's High Arctic. They included measurements of oxygen
isotopes found in the cellulose of fossil tree