Substantial scientific evidence indicates that an increase in the global average temperature of more than 2°F above where we are today poses severe risks to natural systems and human health and well-being. To avoid this level of warming, the U.S. needs to reduce heat-trapping emissions by at least 80 percent below 2000 levels by 2050. Delay in taking such action will require much sharper cuts later, which would likely be more difficult and costly