Flying into the future: aviation's climate challenge

Aviation is representing approximately 3.5% of the total current radiative impact on climate, despite being responsible for only 2.4% of global annual emissions of CO₂. The recent COVID-19 pandemic had a small climate effect and is projected to only delay aviation’s contribution to warming. Aviation is also responsible for non-CO₂ emissions, one of the main concerns over aviation’s effects on climate. These emissions affect atmospheric composition and change cloudiness, which in turn affects the radiative balance of the atmosphere. The largest non-CO₂ effects from aviation on climate are the formation of contrail cirrus and the effects on atmospheric chemistry from NO_x emissions. The net non-CO₂ effects represent approximately 2/3 of the total aviation forcing to date, but their future contribution might change.

Unlike greenhouse gases, contrails (line shaped clouds formed by aircraft) are an easily visible human-driven warming of the climate system. The total magnitude of the warming from contrails is highly uncertain, but is approximately equal to the warming from all greenhouse gases emitted from every aircraft since the dawn of flight. 

The shutdown in aviation due to the COVID-19 pandemic and new satellite data provide a unique opportunity to measure the warming impact of aviation on the climate. From tracking the impact of individual aircraft to observing large scale changes in cloud, satellites find large impacts of aviation on clouds and show us which types of aircraft have particularly large warming impacts on the climate. With a wide range of initial conditions, contrails can also give us an insight into the impact of aerosol perturbations on natural cirrus clouds.