# The climate opportunities and risks of contrail avoidance

## TL;DR

Avoiding contrails from airplanes can significantly reduce future warming, but delaying action reduces its effectiveness.

## Contribution

Quantifies the climate benefits of contrail avoidance and highlights the risks of inaction.

## Key findings

- Contrail avoidance could recover 9% of the global temperature budget by 2050.
- Every year of delay reduces recoverable warming by 0.6%.
- Inaction poses a greater climate risk than the fuel penalties of avoidance.

## Abstract

Navigational contrail avoidance presents an opportunity for rapid reduction in aviation-attributable warming. Here, we use the Aviation Climate and Air Quality Impacts model to evaluate the global temperature changes associated with contrail avoidance towards 2050. If no avoidance is adopted, aviation is projected to contribute 0.040 K of CO2 warming and 0.054 K of contrail warming by 2050. The combined warming from aviation CO2 and contrails is 19% of the difference between current temperatures and the +2 °C limit above pre-Industrial levels, i.e. 19% of our remaining temperature budget. An avoidance strategy phased in over 2035-2045 may recover 9% of this budget, but a 10-year delay may reduce this to 2%. The warming due to additional CO2 emitted during avoidance is two orders of magnitude lower than the expected contrail warming reduction. For every year of delay, the world will be on average 0.003 K hotter in 2050. The most significant climate risk associated with contrail avoidance is therefore inaction.

This study shows that contrail avoidance can recover 9% of the global temperature budget by 2050. For every year of delay, the recoverable warming will diminish by 0.6%. This makes inaction (not fuel penalties) the most significant climate risk associated with avoidance.