Since the late 1990s, many researchers and policy makers have held a two-degree Celsius (3.6-degree Fahrenheit) global temperature increase relative to pre-industrial times as a benchmark limit for global warming, saying that keeping warming below this threshold increases the likelihood that catastrophic changes can be avoided. But we are hardly on track to meet that target, researchers say, and an average global warming of four degrees Celsius (7.2 degrees Fahrenheit) by the end of this century is more likely than two. ... Four degrees would only be a global average. Air over land will warm more than over the oceans, and some places will warm more than others.