Global CO2 levels and temperatures hit record highs in May 2020

The steady rise of carbon dioxide levels in the atmosphere continues unabated. 0n 4th June 2020 scientists from the US National Oceanographic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography at the University of California San Diego announced that the seasonal peak has reached 417 parts per million CO2. The atmospheric carbon dioxide (CO2) levels measured at the Mauna Loa Observatory reached a seasonal peak of 417.1 parts per million in May 2020, the highest monthly reading ever recorded and are now at levels not experienced by the Earth’s atmosphere in several million years.

This NOAA graph depicts the last four complete years of the Mauna Loa carbon dioxide record plus the current year. The dashed red lines represent the monthly mean values, centred on the middle of each month. The black lines represent the same, after correction for the average seasonal cycle. This year’s peak value was 2.4 parts per million (ppm) higher than the 2019 peak of 414.7 ppm  recorded in May 2019. NOAA scientists reported a May average of 417.1 ppm. Scripps scientists reported an May average of 417.2 ppm.

The monthly CO2 levels at Mauna Loa first breached the 400 ppm threshold in 2014, and are now at levels not experienced by the atmosphere in several million years. “Progress in emissions reductions is not visible in the CO2 record,” said Pieter Tans, senior scientist with NOAA’s Global Monitoring Laboratory. ”We continue to commit our planet - for centuries or longer - to more global heating, sea level rise, and extreme weather events every year.” If humans were to suddenly stop emitting CO2, it would take thousands of years for our CO2 emissions so far to be absorbed into the deep ocean and atmospheric CO2 to return to pre-industrial levels.

This latest CO2 data shows no apparent response to economic impact of coronavirus. The rate of increase during 2020 shows no reduction in CO2 pollution emissions due to the current sharp, worldwide economic slowdown in response to the coronavirus pandemic. The reason is that the drop in emissions would need to be large enough to stand out from natural CO2 variability, caused by how plants and soils respond to seasonal and annual variations of temperature, humidity, soil moisture, etc. These natural variations are large, and so far the emissions reductions associated with COVID19 do not stand out. If emissions reductions of 20 to 30 percent were sustained for six to 12 months, then the rate of increase of CO2 measured at Mauna Loa would be slowed. 

“People may be surprised to hear that the response to the coronavirus outbreak hasn’t done more to influence CO2 levels,” said geochemist Ralph Keeling, who runs the Scripps Oceanography program at Mauna Loa. “But the build-up of CO2 is a bit like trash in a landfill. As we keep emitting, it keeps piling up. The crisis has slowed emissions, but not enough to show up perceptibly at Mauna Loa. What will matter much more is the trajectory we take coming out of this situation.” 

Even though terrestrial plants and the global ocean absorb an amount of CO2 equivalent to about half of the 40 billion tons of CO2 pollution emitted by humans each year, the rate of CO2 increase in the atmosphere has been steadily accelerating. In the 1960s, the annual growth averaged about 0.8 ppm per year. It doubled to 1.6 ppm per year in the 1980s and remained steady at 1.5 ppm per year in the 1990s. The average growth rate again surged to 2.0 ppm per year in the 2000s, and increased to 2.4 ppm per year during the last decade. “There is abundant and conclusive evidence that the acceleration is caused by increased emissions,” Tans said.

The Mauna Loa observatory in Hawaii has provided scientists throughout the world with access to the longest unbroken record of reference CO2 measurements. Charles David Keeling of Scripps Oceanography, located at the University of California San Diego, began on-site CO2 measurements at a NOAA’s weather building on Mauna Loa in 1958, initiating what has become the longest unbroken record of CO2 measurements in the world. NOAA measurements began in 1974, and the two research institutions have made complementary, independent measurements ever since. 

Mauna Loa is a benchmark sampling location for CO2. Perched on a barren volcano in the middle of the Pacific Ocean, the observatory is ideally situated for sampling well-mixed air - undisturbed by the influence of local pollution sources or vegetation - that represents the global background for the northern hemisphere. The Mauna Loa data, together with measurements from sampling stations around the world, are incorporated into NOAA’s Global Greenhouse Gas Reference Network, a foundational research dataset for international climate scientists. 

Charles David Keeling was the first to observe that even as CO2  levels rose steadily from year to year, measurements also exhibited a seasonal fluctuation that peaked in May, just before plants in the northern hemisphere start to remove large amounts of CO2 from the atmosphere during their growing season. In the northern fall, winter, and early spring, plants and soils give off CO2, causing levels to rise through May. The continued increase in CO2 and the seasonal cycle are the main features of what is known as the Keeling Curve. 

The evidence for rising global CO2 levels and it wider consequences is undisputable. Pieter Tans, senior scientist with NOAA added “Well-understood physics tells us that the increasing levels of greenhouse gases are heating Earth’s surface, melting ice and accelerating sea-level rise,” Tans said. “If we do not stop greenhouse gases from rising further, especially CO2, large regions of the planet will become uninhabitable.”