Many countries, particularly NATO allies, closed their airspace to Russian aircraft after the Ukraine invasion in February 2022, which Moscow reciprocated with retaliatory bans on Western carriers.

This caused an initial drop in flights between North America and Europe to East Asia but as routes adjusted, airlines were forced to take significant detours to avoid Russian airspace.

This meant longer journeys south of Russia or over the Arctic and more fuel burned in the process, said the authors of the study published in the peer-reviewed journal Communications Earth & Environment.

To better understand the environmental consequences, researchers looked at 750,000 flights made between March 2022 and December 2023, representing 1,100 of the roughly 90,000 flights taken every day around the world.

Despite being just a fraction of the total, the extra distance taken by these flights had "a notable impact on aviation's overall carbon footprint", said Nicolas Bellouin, who co-authored the study from the UK's University of Reading.

"These detours added 8.2 million tonnes of CO2 to global aviation emissions in 2023," said Bellouin, a climate scientist currently studying aviation's climate impact at the French Pierre-Simon Laplace Institute.

These large detours increased global carbon dioxide (CO2) emissions from aviation by one percent in 2023.

"On average, a deviated flight emits 18 extra tons of CO2, roughly equivalent to the emissions of one single short-haul flight," said the study, noting that emissions of other pollutants "almost certainly increased as well".

Russian airlines have been operating fewer long-haul flights since 2022 which may have avoided some emissions, the authors noted.

But it was likely more passengers travelling between Europe and Asia were transiting through the Middle East instead of opting for direct flights, the authors said.

This inefficiency meant the geopolitical situation "presents a major obstacle" to the reduction of aviation CO2 emissions, they concluded.