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Covid-19 lockdown effect on global carbon dioxide levels: A needle in a haystack

Zeppelinobservatoriet på Svalbard
Foto: Markus Fiebig, NILU

So far, COVID-19 lockdowns have caused an estimated decrease in human carbon dioxide emissions of around 17%. While the overall impact will depend on the duration of the lockdowns, the current estimate is for an annual decrease of 4-7% assuming the COVID-19 lockdowns end in mid-June 2020.

“This is an estimate”, says scientist Stephen Platt at NILU’s Department of atmosphere and climate. “The question is whether or not we will be able precisely measure the drop in CO2 emissions due to COVID-19?”

CO2 as money in a bank account

When carbon dioxide (CO2) is emitted into the atmosphere it mixes with the rest of the air in a timespan of months to over a year. The atmosphere already contains a lot of CO2; plants need it to grow, and many different processes take up and release CO2, adding to the changes in time and space.

To visualize this, let us relate all the CO2 in the atmosphere to money in a bank account. We can equate CO2 entering our atmosphere to earnings going into our account every year, and natural processes removing CO2 to our yearly expenditure. We don’t save the same amount every year because our income and expenditure vary – just like CO2 emissions and CO2 uptake vary in the real world. Overall, we have spent a little less each year than we have earned, and over time this has built up to a balance of 1 million Norwegian kroner.

“That is as of today”, Platt emphasizes. “If we look back to before anthropogenic emissions started, the balance was at 691.630 Norwegian kroner (NOK). So, for the last 200 years, we have increased the balance by up to 45%.”

According to NILU’s measurements at the Zeppelin Observatory on Svalbard, a part of the integrated carbon observing system (ICOS), there has been a 0.7% yearly increase in CO2 during the last 10 years.

If we return to our bank account analogy, this means that we might have expected to save 5868 NOK (2.43 ppm CO2) this year. But now, the lockdown has impacted our net savings by about 4% in 2020. Compared to a typical year, we will save a little less – around 5634 NOK (2.18 ppm CO2).

“The difference is about 234 Norwegian kroner – a negligible amount”, says Platt.

Covid-19 lockdown effect on CO2 is very small

Figure 1: Average yearly carbon dioxide at the Zeppelin Observatory since 1988.
Figure 1: Average yearly carbon dioxide at the Zeppelin Observatory since 1988 after changing units to give 1 million Norwegian kroner in 2019 on the left axis, and the original CO2 concentration in parts per million on the right axis. Click to enlarge. Source: NILU

What Platt and his fellow climate scientists are able to say about the effect of the lockdown is that the effect on overall greenhouse emissions in 2020 is very small. Carbon dioxide (CO2) will not go down, but likely increase by a little bit less than normal. This is because the decrease in human emissions globally was at about 17% but entering June, we are coming out of the lockdown and returning to ‘business as usual.’

Over the full year this will probably mean about 4-7% less human emissions than a typical year. Then the background variability in CO2 due to normal year to year variation in all of the processes emitting and taking up CO2, i.e. changing land use, feedbacks and biological activity, is likely to hide this signal (see figure 1).

“Nevertheless, as we are curious to see exactly how COVID-19 has impacted our account, we take a look at our budget for the year and see where we didn’t quite manage to save”, says Platt.

He goes on to explain that in the real world there is no precise budget for CO2.

“We don’t know the exact expenditure or the exact earnings. The only number we can measure precisely is the total amount of money in the account. From this we can see that in some years we have a net saving of as little as 1431 NOK and in other years as much as 9085 NOK. This years’ net savings fit well within this range, as seen in figure 2.”

Figure 2: Average yearly carbon dioxide at the Zeppelin Observatory since 2015 after changing units to give 1 million Norwegian kroner in 2019, and projections for the 2020 average.
Figure 2: Average yearly carbon dioxide at the Zeppelin Observatory since 2015 after changing units to give 1 million Norwegian kroner in 2019, and projections for the 2020 average. The upper-lower range is calculated from the average increase over the last 10 years. Including the variability in the time period yields a maximum of 9085 NOK per year and a minimum of 1431 NOK per year (normal range in light blue) and a typical 5868 NOK per year (dashed black line). If the COVID-19 lockdowns would perturb an average year increase by ~4 percent, the overall increase would be 5634 Kr (red line). Source: NILU

Small needle, large haystack

Continuing the bank account analogy, this means that we can look at the total balance, but we still don’t know whether we saved less than normal, because we still don’t know our exact expenditure. There are variabilities within a year and between years.

One such variability regarding CO2 is it’s strong seasonal cycle, because plants grow less in winter and thus take up less CO2. Since there is more land in the northern hemisphere, and hence more plants, CO2 levels reach a maximum during winter  in the northern hemisphere. Even shorter-term variability arises from weather patterns, which can bring air from polluted regions on one day and from clean regions on another.

“Looking at our savings, we tally them up at the end of each year to see how much we saved or lost”, Platt says. “The same goes for CO2, we can’t know in the middle of the year how our net result will be.”

A lot of people are working hard to find the small effect, but it will take a lot of effort to quantify all of the processes contributing to CO2 emission and uptake in order to isolate the effect of the lockdown. One caveat is that we don’t know what the future will bring. It is possible that further lockdowns will be introduced, which would of course increase the effect on emissions. To sum it up: Looking for the effect of COVID-19 is like looking for a (meaninglessly small) needle in a haystack.

”The surprisingly small effect of the lockdowns on emissions, despite severe restrictions, for example in air travel, also highlight the challenges ahead in meeting the Paris Agreement goal of limiting global average warming to 2°C”, Platt concludes.