2017 was the warmest year ever without an El Niño event and the warmest on record for ocean heat content, with record-or near-record low sea ice extent and volume in both the Arctic and the Antarctic, Carbon Brief reports, tracing the factors behind a year that “proved to be so remarkable across the oceans, atmosphere, cryosphere, and surface temperature of the planet.”
The year shattered records for ocean warming dating back to 1958, and ended up the second- or third-warmest since 1850, U.S. Analyst Zeke Hausfather states in a detailed explainer. “Global surface temperatures in 2017 were 1.0 to 1.2°C warmer than temperatures in the late 19th century (between 1880 and 1900), depending on the temperature record chosen,” and “it is striking how warm 2017 was, despite the end of the massive El Niño event that pushed up 2015 and 2016 temperatures. The past three years are well above any prior years’ temperatures, by a margin of more than 0.15°C.”
Although climate models don’t necessarily reflect the timing of El Niño and La Niña episodes in the real world, surface temperatures in recent years “are tracking rather close to the average projection of the climate models included in the latest report from the Intergovernmental Panel on Climate Change,” Hausfather writes.
The record on Arctic sea ice, meanwhile, “shows a clear and steady decline in Arctic sea ice since the late 1970s,” he notes, with record-low extents for much of the first five months of the year. “A typical summer now has nearly half as much sea ice in the Arctic as it had in the 1970s and 1980s,” with sea ice volume coming in about 12,000 cubic kilometres below the total for 1979.
While the Antarctic doesn’t show a clear long-term pattern for sea ice extent, it still hit record lows for much of 2017, Hausfather notes. “There has been a long-term downward trend in summer global sea ice extent, though the trend is less clear in the winter, reflecting the fact that the Arctic shows a clearer long-term trend than the Antarctic.”
In a post this week for Al Jazeera English, Greenpeace International Executive Director Jennifer Morgan stresses that humanity knows what to do to reverse the greenhouse gas emissions that underlie the Carbon Brief analysis. “The good news is that these actions will pay for themselves—by creating jobs, reducing public health costs, and avoiding climate impacts,” she writes.
But “although we’re on the cusp of major change, particularly in the global energy system, we must move beyond incremental change and achieve a positive transformational shift in the world’s energy and land use systems,” she notes. “The next few years are crucial,” and “we have a moral, ethical responsibility to seize the small window of opportunity we still have to make bold and lasting change to deliver true climate security for us all.”