A study showed that ice and snow cover in the Northern Hemisphere is reflecting less sunlight back into space than previously thought, potentially contributing to global warming. Satellite data from 1979 to 2008 indicated that Arctic sea ice, glaciers, winter snow, and Greenland's ice were reflecting less energy back to space. This decrease in reflection exposes darker ground or water, which absorbs more heat. The study estimated that ice and snow in the Northern Hemisphere are now reflecting 3.3 watts per square meter of solar energy back to the upper atmosphere, a reduction of 0.45 watt per square meter since the late 1970s. Mark Flanner, an assistant professor at the University of Michigan and lead author of the study, explained that this reduction in cooling effect is causing the planet to absorb more solar energy. "The team of US-based researchers, as published in the journal Nature Geoscience Sunday, found that the decrease in reflected solar energy due to warming is more significant than what is currently predicted by climate models," he stated. "Their conclusion is that the cryosphere, which consists of ice and snow, is reacting more sensitively to, and also contributing to, more intense climate change than previously believed." With more ground and water being exposed to sunlight, the heat absorbed accelerates the melting of nearby snow and ice. The reduction in Arctic sea ice over the past few decades, attributed mainly to greenhouse gases from human activities such as burning fossil fuels, could result in the disappearance of Arctic sea ice in summers later in this century, impacting indigenous hunting cultures and endangering polar bears and other wildlife, as well as exacerbating global climate change." Flanner stated that drawing conclusions about the future rate of melting, such as Arctic sea ice, from the study was impossible due to it being based on only 30 years of data. He emphasized that climate is influenced by many other factors besides ice shrinkage. These factors include the presence of more clouds in a warmer world, which reflect sunlight, and an increase in water vapor that traps heat in the atmosphere. The study projected that for every degree Celsius rise in temperature, there would be a decrease in solar energy reflected out to space ranging between 0.3 and 1.1 watts per square meter from snow and ice in the Northern Hemisphere. In the last thirty years, temperatures in the Northern Hemisphere have increased by approximately 0.75 degrees Celsius. This study did not examine the Southern Hemisphere, where Antarctica has more ice but is colder and shows less warming. Globally, the Earth absorbs an average of 240 watts per square meter of solar energy annually. If the Northern Hemisphere cryosphere were not present, the planet would be darker and absorb an extra 3.3 watts, according to Flanner.