While this year will be memorable for many reasons, it is now more likely than not that 2020 will also be the warmest year for the Earth’s surface since reliable records began in the mid-1800s. This is all the more remarkable because it will lack any major El Niño event – a factor that has contributed to most prior record warm years.
However, with three months remaining, there is still some uncertainty as there is a chance that a growing La Niña in the tropical Pacific may drive cooler temperatures leading to 2020 being the second warmest on record (although this is more likely to be seen in 2021 temperatures). Either way, it’s not looking good from a climate security perspective.
The first nine months of the year saw record concentrations of major greenhouse gases – CO2, methane, and nitrous oxide – in the atmosphere. Arctic sea ice extent was at record low levels for much of the summer and the summer minimum clocked in as the second lowest on record.
While climate records are a useful benchmark to highlight the warming of the planet, the change in temperatures, sea ice and other climate factors over time are much more important than if any single year sets a new record.
There has been a clear warming trend over the past 50 years, along with hints in some datasets of potential acceleration in recent years. Similarly, both sea ice extent and volume are clearly declining over time.
Carbon Brief has analyzed records from six different research groups that report global surface temperature records: NASA; NOAA; Met Office Hadley Centre/UEA; Berkeley Earth; Cowtan and Way; and Copernicus/ECMWF.
Surface temperature records have shown around 0.9C warming since the year 1970, a warming rate of about 0.18C per decade. During 2020 many of the months have set new temperature records, though the results vary a bit across datasets due to different observations used, adjustments for changes in measurement techniques over time, and methods to fill in gaps between measurements.
Six of the nine months in 2020 – January, April, May, June, July and September – saw record temperatures in at least one of the global surface temperature datasets. All months of the year saw either the second warmest or warmest in at least one dataset and no dataset has any months below the fourth warmest on record.
Greenhouse gas concentrations reached a new high in 2020, driven by human emissions from fossil fuels, land use and agriculture.
Three greenhouse gases – CO2, methane (CH4) and nitrous oxide (N2O) – are responsible for the bulk of additional heat trapped by human activities. CO2 is by far the largest factor, accounting for roughly 50% of the increase in “radiative forcing” since the year 1750. Methane accounts for 29%, while N2O accounts for around 5%. The remaining 16% comes from other factors including carbon monoxide, black carbon and halocarbons, such as CFCs.
Human emissions of greenhouse gases have increased atmospheric concentrations of CO2, methane and nitrous oxide to their highest levels in at least a few million years – if not longer.