US: 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.
NASA Administrator Charles Bolden says, “Climate change is the challenge of our generation, and NASA’s vital work on this important issue affects every person on Earth. Today’s announcement not only underscores how critical NASA’s Earth observation program is, it is a key data point that should make policy makers stand up and take notice – now is the time to act on climate.”
GISS Director Gavin Schmidt adds, “2015 was remarkable even in the context of the ongoing El Niño. Last year’s temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing.”
NASA’s analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions if left unaccounted for. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
NOAA scientists used much of the same raw temperature data, but a different baseline period, and different methods to analyze Earth’s polar regions and global temperatures.