The newly released State of the Climate 2020 has confirmed that last year was among the top three hottest years on record. The wide range of impacts around the world were perhaps most keenly felt across the Arctic.
Looking back to January of this year, agencies such as NOAA, NASA, and the European Union's Copernicus Climate Service had already tallied up global temperatures for all of 2020. Despite the cooling effects of a La Niña developing in the equatorial Pacific Ocean late in the year, 2020 had likely tied with 2016 as the warmest year on record. It was even possible that it may have even beat out 2016 by a very narrow margin, but it was just too close to call for sure.
Global surface temperature each year compared to the 1981–2010 average from three datasets: NOAA (red line), NASA (orange), and University of East Anglia (pink). The background image from the NOAA DISCOVR/EPIC mission shows Hurricane Laura coming ashore in Louisiana on August 26, 2020. Image by NOAA Climate.gov, adapted from State of the Climate in 2020. Credit: NOAA Climate.gov
Following those initial broad-brush assessments, climate scientists from around the world used their respective expertise to dive into the details of what had happened throughout 2020. They catalogued extreme events and severe conditions across the globe, examining everything from heat waves and droughts, to tropical cyclones and ocean patterns, to the loss of snow and ice across the planet's polar regions.
All of that collective knowledge has now been gathered into the new State of the Climate 2020 report, released this week by the Bulletin of the American Meteorological Society.
"Nothing is a surprise," says Dr. Chris Derksen, a research scientist with Environment and Climate Change Canada who contributed to the report. "All the extreme events that were experienced globally over the past year are completely in line with what we've been expecting, and with what climate models have projected."
Numerous climate extremes were catalogued in 2020. Credit: NOAA NCEI
According to the report, the concentration of carbon dioxide in the atmosphere reached a new high during 2020 — 412.5 parts per million — even with the societal and economic slowdowns due to the pandemic. Global temperatures were 0.54°C to 0.62°C above the 1981–2010 average, putting the year firmly within the top three hottest years on record (along with 2016 and 2019).
Global sea level rose to its highest point since modern record-keeping began. Meanwhile, heat content of the upper layers of the world's oceans reached record highs last year.
Global sea level rose for the ninth consecutive year, due to a combination of melting glaciers and ice sheets, and thermal expansion of the ocean layers, resulting in a record high of 91.4 millimetres. Credit: NOAA Climate.gov/SOTC 2020
Across the Arctic, surface air temperatures soared to their highest yearly average on record — 2.1°C above the 1981–2010 average, over 3 times higher than the overall global average temperature change since the beginning of the 20th century. Permafrost temperatures also reached their highest on record.
Sea ice melted away to its smallest extent of the past eight years, and was second smallest only to 2012 in the entire 41 years of satellite measurements.
Temperatures across the Arctic are rising much faster than the global average. Credit: SOTC 2020 (adapted from Jones et al. 2012)
What is more, snow cover in the Arctic was again below average, with an extreme spring heat wave across Siberia melting away so much snow so quickly that the region had the smallest snow cover extent of the past 54 years.
This extreme heat wave was brought about by an especially strong polar jet stream, which spun in a tight circle around the highest regions of the Arctic. This allowed warm air to surge north over Siberia and remain there for an extended period of time. However, it could have easily happened on this side of the world, instead.
"Over the past decade we've had record setting events on the North American side of the Arctic, but this past [year] it just so happened that the record-setting event happened on the Eurasian side," said Derksen. "Still, over the long time period, it's the same direction of change over the entire Arctic, no matter which side of the Arctic you're on, towards this earlier snow melt."
These maps reveal how snow cover duration changed in the Arctic, from (a) August 2019 – January 2020, and (b) February – July 2020, compared to the 20 years prior. Oranges and reds denote longer than average snow cover, with purples representing shorter than average snow cover duration. While changes over the North American Arctic were more moderate, the spring melt over Siberia was much more severe. Credit: SOTC 2020
This heat wave and the early loss of snow cover over Siberia primed conditions for the resulting extreme wildfires that broke out in the region during summer 2020.
At the opposite end of the world, an extreme summer heat wave across Antarctica produced the highest temperature ever recorded on the continent — 18.3°C at Esperanza Station on February 6. It also resulted in the largest late-summer surface melt seen since record keeping began, 43 years ago.
Towards the end of southern winter, a strong polar vortex set up around the Antarctic continent, causing significant cooling of the stratosphere and opening up an unusually large ozone hole which persisted for much longer than usual. Most Antarctic ozone holes close up sometime in late November or early December. The 2020 ozone hole was finally reported to be completely closed as of December 28. That makes it the most persistent ozone hole ever recorded.
CLIMATE CHANGE IS HAPPENING NOW
While these impacts are not unexpected, what has changed, according to Derksen, is perhaps the perception that climate change will only affect future generations.
"When you look at the extreme heat events that we've had in Canada, just this past summer, these are extreme events that are driven by climate change, and this is something we need to adapt to, and we're dealing with now," Derksen explained.
Thumbnail credit: Ulrik Pedersen/NurPhoto via Getty Images