The numbers are in, and they are unforgiving: 2015 was the hottest year on record, and it wasn’t even close. The announcement was expected—scientists monitoring global temperatures predicted before the end of the year that 2015 would set a record for warmth, in part because of the massive El Niño event currently under way in the Pacific Ocean. But the data released today confirm that human-induced global warming is pushing temperatures higher at an alarming rate: 2014 was the previous record holder for global average surface temperature, clocking in at 0.57 °C above the 1960 to 1990 average, but last year was 0.75 °C above that average.
If that doesn’t sound like a big jump, consider that the agreement reached at the U.N. climate summit in Paris last year aims to limit warming to 2 °C above preindustrial levels. The good news is that the agreement represents the first global effort to try to curtail greenhouse-gas emissions. The bad news is we’re already half way to that 2 °C target. Worse, the figures released today could be underestimates, and even if the Paris agreement is upheld we could be headed for much more warming, unless we get even more ambitious in our emissions targets.