Ice sheets, caps, glaciers, and icebergs are getting intense study from scientists seeking to understand how global climate change will impact the ice–and how fast.

In the Arctic, an international team measured ancient temperatures from the Pliocene Epoch on Canada’s Ellesmere Island and found that CO2 levels of approximately 400 parts per million produced annual temperatures in the region of 32 degrees Fahrenheit (0 degrees Celsius). According to a press release from the University of Colorado at Boulder, Arctic temperatures may be exceedingly sensitive to human-induced carbon dioxide emissions.

Ashley Ballantyne of the University said current levels of CO2 in the atmosphere of approximately 390 parts per million may be approaching “a tipping point for irreversible ice-free conditions in the Arctic.” He adds that it becomes difficult to maintain permanent sea and glacial ice in the Arctic when temperatures reach 0 degrees Celsius. Greenhouse gases are up from about 280 parts per million in the pre-industrial era and Arctic temperatures have risen by about 1 degree Celsius in the past two decades. Ballantyne says this trend is expected to continue in the coming decades and centuries.

The team reported its findings in the July issue of Geology. Three methods were used to measure the ancient temperatures: measurement of oxygen isotopes in the cellulose of fossil trees and mosses to reveal temperatures and precipitation levels; an analysis of the distribution of lipids in soil bacteria which correlate with temperature; and an inventory of ancient Pliocene plant groups that overlap in range with contemporary vegetation.

At the Ellesmere Island site, called Beaver Pond, trees, plants and mosses from earlier times had been preserved in peat deposits, allowing for detailed analyses. Mollusks and insect fossils and vertebrate remains are also found at the site.

Today, Ellesmere Island is a polar desert with little vegetation and a few small mammals. Temperatures range from roughly minus 37 degrees Fahrenheit, or minus 38 degrees Celsius, in winter to 48 degrees Fahrenheit, or 9 degrees Celsius, in summer. The region is one of the coldest, driest environments on Earth.

The scientists have expressed concern that a proposal for mining coal near the site would destroy a valuable resource for research into the planet’s past, including its ice ages.

In Antarctica, researchers are also looking at the Pliocene Epoch for clues to how quickly ice formations might melt as Earth’s temperatures rise.

The West Antarctic Ice Sheet has been closely watched as its outlet glaciers lose ice rapidly. It had been thought that the East Antarctic Ice Sheet was not as vulnerable to climate change.

Writing in the June 25 issue of Science, Douglas Fox says scientists are looking at evidence that suggests the larger and thicker eastern ice sheet may not be stable if conditions during the middle Pliocene recur. That period “… saw carbon dioxide levels and temperatures that many scientists say could recur by 2100.”

He cites three studies using different remote-sensing methods that show the sheet is losing ice. Records of partial melting in East Antarctica during the Pliocene raised sea levels.

One survey, called ICECAP, is mapping the subglacial topography and finds troughs under East Antarctica glaciers, plunging as far as 1,400 meters (0.86 miles) below sea level. The troughs allow warm water deep under the glaciers and accelerate their flow to the sea. It had been thought that the East Antarctic glaciers sat above sea level and would not be affected by changes in ocean waters.

Fox points out that there are many questions to be answered about the East Antarctica Ice Sheet and what effect its melting would have on the oceans and on human populations.