Two US government agencies have confirmed what climate experts have long suspected. 2015 was the hottest year in Earth’s history, since record-keeping began in 1880. Analysts at the US National Oceanic and Atmospheric Administration and NASA say that the average temperature across the entire planet last year was 1.62 degrees Fahrenheit above the 20th century average. This is more than 20% higher than the previous highest departure from average. In fact, for much of the Northern Hemisphere, last December looked and felt more like a March or April.
So, why was 2015 so warm? The huge El Niño was a major driver of the heat, but it wasn’t the only factor. NASA insists that the change was “largely driven by increased carbon dioxide and other human-made emissions into the atmosphere.” And if greenhouse gas emissions are not cut urgently, 2016 could push the chart-topping temperature climb even higher.