The Climate Opportunities and Risks of Contrail Avoidance

Navigational contrail avoidance presents an opportunity for rapid reduction in aviation-attributable warming. We use the Aviation Climate and Air Quality Impacts model to evaluate the global temperature changes associated with avoidance towards 2050. If no avoidance is adopted, aviation is projected to contribute 0.1 K of warming by 2050: 0.04 K from CO ₂ and 0.06 K from contrails. This is 20% of the difference between current temperatures and the +2 °C limit above pre-Industrial levels, i.e. 20% of our remaining temperature budget. An avoidance strategy phased in over 2035-2045 may recover 10% of this budget, but a 10-year delay may reduce this to 2%. When the additional CO2 emitted during avoidance is accounted for, there is <0.01% chance of a net warming. For every year of delay, the world will be on average 0.004 K hotter in 2050. The most significant climate risk associated with contrail avoidance is therefore inaction.