World levels of carbon dioxide have fallen significantly during the first six months of this year as a result of the COVID-19 pandemic.

Researchers at the Potsdam Institute for Climate Impact Research in Germany said in a study the world experienced an 8.8% drop in CO2 emissions compared with the same period in 2019. The decrease was equivalent to 1.55 billion metric tons.

This decline in CO2 emissions was larger than the reductions during the recession of 2008, the oil crisis of 1979 and World War Two.

The study provides a more precise look at COVID-19's effect on international energy consumption compared with previous analyses. It suggests fundamental steps that might be taken to stabilize the world's climate in the aftermath of the pandemic.

"What makes our study unique is the analysis of meticulously collected near-real-time data," said lead author Zhu Liu from the department of earth-system science at Tsinghua University in Beijing.

He said the research team was able to get a much faster and more accurate overview, including timelines that show how emissions decreases have corresponded to lockdown measures in each country by looking at the daily figures compiled by the Carbon Monitor research initiative.

He said emissions in April decreased by 16.9 % at the height of the first wave of COVID-19 when many large countries shut down public life and parts of their economies to control the disease's spread.

Zhu said outbreaks worldwide resulted in emission drops "that we normally see only on a short-term basis on holidays such as Christmas or China's (Lunar New Year)."

The study shows which parts of the world economy were most affected by the decline in CO2 emissions. The largest was observed in land transport - which saw CO2 emissions fall 40% worldwide largely owing to people working from home.

The power sector experienced a 22% fall in emissions while industry, aviation and shipping saw emissions drop by 17 %. Surprisingly, the residential sector saw a small emissions drop of 3 % largely because the abnormally warm winter in the Northern Hemisphere led to a drop in heating energy consumption.

The declines in CO2 emissions were short-lived, however. By July, when more countries eased lockdown measures, most economies returned to their usual levels of CO2 emissions. The study, however, pointed out that even if these countries remained at their historically low levels this would have a minuscule effect on the long-term CO2 concentration in the atmosphere.

"While the CO2 drop is unprecedented, decreases of human activities cannot be the answer," said joint author Hans Joachim Schellnhuber, the founding director of the Potsdam Institute for Climate Impact Research.

"Instead we need structural and transformational changes in our energy production and consumption systems. Individual behavior is certainly important, but what we really need to focus on is reducing the carbon intensity of our global economy."

The study was published in the latest issue of Nature Communications.

A similar drop in CO2 emissions was reported in May. A study published in the British journal Nature reported lockdowns had an "extreme" effect on daily carbon emissions."

Lockdowns and other restrictions resulted in a 17% drop worldwide during peak confinement measures in early April - levels last seen in 2006. The report said benefits were unlikely to last. The researchers said this brief pollution break will likely be "a drop in the ocean."