Last month tied July of 2016 for the hottest month on record, according to a new analysis from researchers at NASA's Goddard Institute for Space Studies. Sixteen of the 17 hottest years on record have occurred in the 21st century, including 2015 and 2016, both of which saw a temperature boost thanks to a strong El Niño event. (El Niños bump up surface temperatures by churning warm water to the ocean surface.) Record-setting temperatures in 2017 are especially concerning now that there is no El Niño; in other words, most of the excess heat this year is due to human-induced climate change.