The 15 years from 1998–2012 were the warmest on record at that time, but the rate of global surface warming was slower than it had been in the 2-3 decades prior thanks to several natural influences. Meanwhile, the ocean's heating imbalance continued to climb.
Global atmospheric carbon dioxide reached 405.0 parts per million (ppm) in 2017, a new record high. In the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.6 ppm per year. Over the past decade, however, the growth rate has been closer to 2.3 ppm per year.
As part of the State of the Climate in 2017 report, experts describe a record three-year-long episode of mass coral bleaching at tropical reefs worldwide. Previous global bleaching events required the presence of El Niño, but the devastating 2014–2017 event began before El Niño emerged and continued long after it ended—implicating human-caused global warming in the mass die offs.
The ocean absorbed a net 2.6 billion tonnes of carbon from human activities, which is 36% higher than the 2005-2015 average. While ocean carbon uptake slows atmospheric warming, it also continues the trend of ocean acidification, which stresses shell-building creatures and other ocean life.
The heating imbalance in Earth's oceans reached a new record high in 2017. From 1993–2017, the ocean has accumulated 0.36–0.40 watts of heat per square meter in the top 700 meters and another 0.19–0.35 watts per square meter at depths between 700–2,000 meters.
2017 will likely be the 38th year in a row that, on average, glaciers worldwide have lost ice mass. Cumulative mass losses have accelerated since 2000.
In 2017, land areas recorded more than 60 days of extreme daytime heat worldwide, nearly double the 1961-1990 average.
Large areas of severe or extreme drought affected every continent except North America in 2017. Extreme drought conditions affected at least 3 percent of the global land area in every month of 2017.
Global mean sea level in 2017 was the highest in the satellite record—3 inches (77 millimeters) higher than it was in 1993—and the rate of increase has been accelerating.
