Start flying!
KLM, like other EU company`s, wants to fly. The beancounters, pennlickers, civil servants are not taken scientific studies from NASA into account. CAA and Eurocontrol are slow working government bodies.
Aircraft avoid visible ashclouds or known positions of clouds. Dispersing ash over the globe are not visible ashclouds and do not influence aircraft performance as demonstrated by aircraft returning to their base.
When Pinatubo and other dangerous vulcanos errupted the airspace was NOT closed. Warnings for air traffic were NOTAMed. Those aerosol clouds dispersed around the world and affected global weather.The density of the aerosols was and is not large enough to affect a/c engines. Aircraft kept on flying.