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Met Office: Atmospheric CO2 is now 50% higher than preindustrial levels
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Met Office: Atmospheric CO2 is now 50% higher than preindustrial levels


The atmospheric levels of carbon dioxide (CO2) are now 50% higher than the levels at which humanity began large-scale fossil fuel burning during the 1970s. industrial revolution

Recent measurements from the Mauna Loa observatoryThe results from Hawaii show that atmospheric CO2 levels reached 417 parts per million (ppm) for several days between February 2021 and March 2021. Pre-industrial levels were around 278ppm.

In the coming weeks, CO2 levels are expected to rise further. Therefore, 2021 will be the first year in which CO2 levels are more than 50% higher than pre-industrial levels.

Monitoring the CO2 buildup

Record derived from ice core measurementsIt was found that the average global CO2 concentration of the atmosphere from 1750 to 1800 was approximately 278ppm. This is the value at which the Intergovernmental Panel on Climate Change(IPCC) was used as the preindustrial baseline for CO2 in its fifth assessment report(pdf), Published 2013-14 

Atmospheric CO2 has been rising ever since – driving ongoing warmingThe global climate. Now, in March 2021, levels have reached around 417ppm – a 50% increase over the 1750-1800 average.

The plot below shows atmospheric CO2 levels ranging from 1700 to 2021. This is based on ice core dataBefore 1958, then the instrumental recording at Mauna Loa starting in the Scripps CO2 programThe 2021 CO2 forecast is available from the Met Office. (The apparent shift in 1958 is due to the inability of instrumental records to capture the seasonal cycle observed in ice core records.

Global atmospheric CO2 concentrations from 1700 to 2021
Global atmospheric CO2 concentrations, 1700-2021 Credit: Met Office.

The human-driven CO2 rise is, therefore, halfway towards “doubled-CO2” – the long-standing benchmark for quantifying long-term future global warming in terms of Equilibrium Climate Sensitivity(ECS). 

Systematic long-term measurements of atmospheric CO2They were established in 1958 by Charles David KeelingAt the Mauna Loa Observatory, Hawaii. This CO2 record is the data behind the iconic “Keeling Curve”.

Since then, additional measurement locations around the globe have allowed the global average CO2 concentrationTo be estimated. These records, along with the ice-core data, show many important things. 

First, the average annual CO2 concentration is rising year-on-year. This is mainly due the burning of fossil fuels and further contributions from deforestation. 

Second, as human-driven CO2 emissions have increased, so has the pace of increase in CO2. It took more than 200 years for the increase to 25% by 1986. By 2011 – 25 years later – the increase reached 40%. It is now at 50% after a further ten years. 

Third, there is always a clear seasonal swing between atmospheric CO2 levels. The Mauna Loa record shows a peak in May, and a low point in September. This is because the vegetation takes up CO2 during the growing seasons and releases it in autumn and winter.

A 50% increase of CO2

For a few days in May, scientists measured CO2 concentrations at Mauna Loa of 417ppm. In 2021, 417ppm was measured for several days in February, March, and April. But the usual springtime upward trend is expected to soon lead to concentrations higher than this level for the next three-to four months.

2021 will be the first year with CO2 levels greater than 50% than pre-industrial levels, and this is expected to last for more than a few days. 

The Met Office predicts that the monthly average CO2 at Mauna Loa will peak at 419.5ppm (±0.6) in May, after which it is expected to temporarily drop back down below 417ppm from around late July onwards. It is expected to drop to 417ppm by the end of the year. 

The plot below shows the annual cycle for atmospheric CO2 levels. The graph below shows the annual cycle for atmospheric CO2 levels. The 2021 forecast has been shown in red.

Observed and forecast monthly and annual CO2 concentrations at Mauna Loa.
Mauna Loa’s CO2 concentrations were observed and forecasted monthly and annually. Observations from the ScrippsCO2 program, forecasts starting Met Office. Credit: Met Office.

Overall, the annual average CO2 concentration for 2021 is predicted to be 416.3ppm (±0.6). With the annual rise being about 2.5ppm – even last year when emissions fell sharply due to economic impacts of the Covid-19 pandemic – it is clear that 2022 will be the first year with the annual average CO2 at 50% above pre-industrial levels.

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