Governments vowed to keep global warming "well below" 2 degrees Celsius (3.6 degrees Fahrenheit) compared with preindustrial times. But even 2 degrees of warming could threaten the existence of low-lying island nations faced with rising seas. So governments agreed to try to limit warming to 1.5 degrees C (2.7 degrees F), which is just half-a-degree above the global average temperature this year.