All five of the hottest years on record have occurred in the last five years, according to global temperature data released Wednesday by NASA and the National Oceanic and Atmospheric Administration.
While 2018 was slightly cooler than the three prior years, Earth still had its fourth-warmest year since scientists began keeping records in 1880, the federal agencies said. Their separate analyses add to decades of evidence that the burning of fossil fuels, the clearing of forests and other human activities are releasing heat-trapping greenhouse gases into the atmosphere and causing the planet to warm.
If you smooth out these year-to-year variations and look at the big picture, the overall trend in the past few decades is one of accelerating change, said Alex Hall, who directs the Center for Climate Science at UCLA and was not involved in either government analysis. We are seeing more and more warming that is happening at a faster and faster rate.
Last years average global surface temperature was 1.42 degrees Fahrenheit above the 20th-century average, according to NOAA.
The warmest year was 2016, followed by 2017, 2015, 2018 and 2014, according to NASAs rankings.
All five of those years were exceptionally warm, with only slight differences that were driven by natural variations in the weather, including the alternating cool and warm cycles from El Nino and La Nina.
You get ups and downs years that are a little bit warmer, a little bit cooler but the long-term underlying trend is very, very clear, said NASA climatologist Gavin Schmidt, who worked on the space agencys analysis. Its the long-term trends that are having impacts on ice, on severity of droughts, on heat waves, on sea level rise and wildfires.
The combination of rising greenhouse gases and a mild El Nino underway in the Pacific Ocean means its likely that 2019 will be hotter than 2018. Scientists say theres a very good chance this year will wind up ranking among the top five hottest on record, barring an abrupt planet-cooling event such as a giant volcanic eruption.
NOAA and NASA each analyze temperature measurements from thousands of sites around the world, including weather stations on land and ships and buoys spread across the worlds oceans.
The two agencies use much of the same data but perform independent analyses with minor differences in methods that yield slightly different rankings. NASA, for instance, ranked 2015 as the third-warmest year on record while NOAA found it was 2017. But in the long-term, the two agencies strongly agree on the pace and trajectory of global warming.
Temperatures in 2018 were higher than average across much of the globe, including most of the lower 48 United States, and the Arctic is warming two to three times faster than the global average, federal scientists said. Those higher temperatures continue to drive the decline in sea ice in the Arctic. The average annual sea ice extent was 4 million square miles in 2018, the second smallest extent in records going back to 1979, NOAA reported.
Those observations are at odds with President Donald Trumps statements attacking the scientific consensus on climate change. Icy cold weather across the Midwest and Eastern U.S. last week prompted Trump to tweet a plea to global warming: Please come back fast, we need you!
Scientists say such remarks confuse short-term natural variations that is, weather with long-term shifts in the climate that are driven by human activity. Indeed, that natural variation is why climate scientists look primarily at temperature trends over long timescales and dont give too much significance to a single hot or cold year.
But these are warm years that have persisted over a five-year period, and they sit on top of a longstanding, increasing trend over the last one-and-a-half centuries, said Waleed Abdalati, director of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder who was not involved in the federal reports. Thats a clear upward signal. It drives home the point that this trend is robust.
Global warming is also increasingly evident in local measurements, where daily records for high temperatures are toppling more than twice as often as daily records for low temperatures, said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research.
