Grégoire Dannet’s research while affiliated with Institut Pierre-Simon Laplace and other places

As air traffic rebounds from its large drop during the Covid-19 crisis, civil aviation needs to continue addressing its climate impact. Knowledge of aircraft trajectories is essential for an accurate assessment of the CO2 (and non-CO2) climate impact of aviation. Here we combine an aircraft trajectory optimization algorithm and a global database of aircraft movements to quantify the impact of airspace restrictions due to conflict zones on CO2 emissions. Among current restrictions, we show that the Russian ban of its airspace to Western airlines following the invasion of Ukraine has the largest impact. Our analysis reveals an initial reduction of flights to and from East Asia that would have crossed the Russian territory. Routes then gradually reopened by making a detour, which led to an average increase in fuel consumption of 13% on the affected routes, with a greater impact for flights to and from Europe (14.8%) compared to flights to and from North America (9.8%). Although these flights represent only a small fraction of the daily flights, the large detours have increased global aviation CO2 emissions by 1% in 2023, equivalent to a quarter of the yet-to-be-achieved efficiency gain potential from improved air traffic management.

Aviation, as a critical component of the global transportation infrastructure, has experienced substantial growth over the past few decades, facilitating the movement of people and goods. However, this sector is also a significant consumer of fossil fuels and contributor to global warming. In this study, we estimated the carbon dioxide (CO$_2$) emissions from global aviation for the period between 2019 to June 2024 using Automatic Dependent Surveillance-Broadcast (ADS-B) data. We estimate that a yearly total of 42 million of flights were responsible for 895 Mt of CO$_2$ emissions in 2019. Flight disruptions caused by the Covid-19 pandemic have decreased emissions during the years 2020–2023, but the recovery has been quick: the number of domestic flights in 2023 surpassed its pre-Covid level while international flights were slightly lagging behind. This results in CO$_2$ emissions in 2023 that were still 9% below their pre-Covid levels. However, traffic and emissions levels calculated for 2024 indicate a return to pre-Covid levels. Our analysis indicates that North America, Europe, and Asia account for almost 75% of the aviation CO$_2$ emissions. Flights shorter than 2600 km are responsible for 50% of the aviation CO$_2$ emissions worldwide. Flights longer than this distance account for the other half of emissions, although they represent less than 15% of the total number of flights. The most recent generation of aircraft represented 20% of the fleet at the start of 2024, resulting in an 8% gain in efficiency, equivalent to 144 Mt CO$_2$ avoided over the whole period. However, the ongoing growth in traffic delays the fleet renewal and hinders the reduction in emissions. Aviation does not appear to be on track to reach a 55% reduction in emissions by 2030. Additionally, if sustainable aviation fuels are to be used, this will require a substantial increase in biomass or low-carbon electricity use.

Cities in China are on the frontline of low-carbon transition which requires monitoring city-level emissions with low-latency to support timely climate actions. Most existing CO2 emission inventories lag reality by more than one year and only provide annual totals. To improve the timeliness and temporal resolution of city-level emission inventories, we present Carbon Monitor Cities-China (CMCC), a near-real-time dataset of daily CO2 emissions from fossil fuel and cement production for 48 major high-emission cities in China. This dataset provides territory-based emission estimates from 2020-01-01 to 2021-12-31 for five sectors: power generation, residential (buildings and services), industry, ground transportation, and aviation. CMCC is developed based on an innovative framework that integrates bottom-up inventory construction and daily emission estimates from sectoral activities and models. Annual emissions show reasonable agreement with other datasets, and uncertainty ranges are estimated for each city and sector. CMCC provides valuable daily emission estimates that enable low-latency mitigation monitoring for cities in China.