A Look at 2017: Takeaway Points from the State of the Climate Supplement
warmest annual global temperature since records began in the midto late 1800s and makes it the warmest non–El Niño year on record, as El Niño–Southern Oscillation (ENSO) conditions were neutral through much of 2017, with weak La Niña conditions at the start and end. The four warmest years on record have occurred since 2014. Above Earth’s surface, the annual globally averaged lower-tropospheric temperature (the bulk atmosphere below 10-km altitude) in 2017 was, depending on the dataset, 0.38° to 0.58°C above the 1981–2010 mean. This was a decrease of more than 0.1°C from the 2016 record-high level. Similarly, the 2017 globally averaged lower stratospheric temperature was 0.2°C greater than its record-low 2016 value but still below normal, with an anomaly of approximately −0.4°C (variation among datasets was ± 0.2°C). The year saw a wide swing of precipitation extremes, with some areas experiencing remarkable tropical and post–tropical cyclone precipitation, while others were affected by extended droughts. After a significant peak in global drought area in 2016, the drought area fell sharply in early 2017 before rising to above-average values once again later in the year. At least 3% of the land area was affected by extreme drought conditions in each month of 2017, and this is the fourth greatest monthly percentage of severe drought since 1950 (after 1984, 1985, and 2016). Severe drought conditions in British Columbia, Canada, contributed to its most extensive wildfire season on record. On the high end of the precipitaGLOBAL CLIMATE. The dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—increased once again in 2017, reaching new record highs. The annual global average carbon dioxide concentration at Earth’s surface for 2017 was 405.0 ± 0.1 ppm. This was 2.2 ppm greater than 2016 amounts and was the highest in the modern atmospheric measurement record and in ice core records dating back as far as 800,000 years. The global growth rate of carbon dioxide has nearly quadrupled since the early 1960s. The rise in globally averaged levels of methane from 2016 to 2017 was 6.9 ± 0.9 ppb, and the mean global atmospheric nitrous oxide levels rose 0.9 ppb from 2016 to 2017. Both increases were comparable to the average yearly growth rate of each gas over the last 10 years. Global surface temperatures were 0.38°–0.48°C above the 1981–2010 average, depending upon the dataset used. This places 2017 as the second or third