Within the next five years, the world is likely to experience at least one year in which the global average surface temperature exceeds 1.5°C above pre-industrial levels. It was sharp forecast from the World Meteorological Organization (WMO) this week in his climate forecast.  Straying above 1.5 °C could lead to potentially irreversible effects on the global climate system , scientists warned, including the collapse of the Greenland and West Antarctic ice sheets, the sudden melting of permafrost, rising sea levels and the bleaching of coral reefs. For these reasons is the 1.5°C limit at the heart of the 2015 Paris climate agreement , which commits countries to keeping global temperature increase "well below 2°C" and "making efforts" to 1.5°C.