Scientists have identified the ecological systems most at risk from climate change in a study published today in the journal Proceedings of the National Academy of Sciences. The researchers warned that within 100 years, a series of tipping points could occur that will significantly alter important ecological systems. Most at risk, according to the study: Arctic sea ice and Greenland’s ice sheet. Within 10 years summer Arctic sea ice may no longer form, and not long after that, Greenland’s massive ice sheet could begin to irreversibly melt; a complete melt could take 300 years, raising sea level by some 20 feet. Other tipping points likely to be reached this century include collapse of the West Antarctic ice sheet, an intensifying El Nino weather pattern, collapse of the Indian monsoon, significant dieback of the Amazon rainforest, and rapid deterioration of northern boreal forests. Lead author Tim Lenton emphasized the risks of abrupt ecosystem decline, but remained optimistic. “If we know when the different tipping points are, we can use them to inform targets to limit global warming. It gives us something to aim for.”