Nations must make more aggressive pledges to slash greenhouse gas emissions to avoid global temperatures rising by 2 degrees Celsius and prevent the worst possible effects of climate change, the United Nations Environment Program (UNEP) warns in a new report. The study, based on expert estimates from nine leading research centers, suggests that annual greenhouse gas emissions around the world should not exceed 40 to 48.3 gigatons of carbon dioxide equivalent in 2020 and should peak sometime between 2015 and 2021. In addition to remaining within that range, the report also states that global emissions need to be cut by between 48 percent and 72 percent between 2020 and 2050 to even have a 50/50 chance of meeting the target of keeping global temperatures below 2 degrees Celsius. “There are clearly a great deal of assumptions underlying these figures, but they do provide an indication of where countries are and perhaps more importantly where they need to aim,” said UNEP Executive Director Achim Steiner. “There clearly is a ‘gigaton gap’ which may be a significant one according to some of the modelers.”