The Earth is so hot this year that a limit for global warming agreed by world leaders at a climate summit in Paris just a few months ago is in danger of being breached.
In December, almost 200 nations agreed a radical shift away from fossil fuels with a goal of limiting a rise in average global temperatures to well below 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times while "pursuing efforts" for 1.5C (2.7F).
But 2016 is on track to be the hottest year on record, also buoyed by a natural El Nino event warming the Pacific, according to the U.N.'s World Meteorological Organization. The first six months were a sweltering 1.3C above pre-industrial times.
"It opens a Pandora's box," said Oliver Geden, of the German Institute for International and Security Affairs. "The future debate about temperature targets will be about overshoot."
Many climate scientists say the Paris targets are likely to be breached in the coming decades, shifting debate onto whether it will be possible to turn down the global thermostat.