In a fascinating example of unintended consequences, scientists now believe that the heat waves this summer have been caused by rules put in place in 2020 to reduce air pollution from cargo ships.

Sulphur particles contained in ships’ exhaust fumes have been counteracting some of the warming coming from greenhouse gases. But lowering the sulphur content of marine fuel has weakened the masking effect, effectively giving a boost to warming.

https://www.carbonbrief.org/analysis-how-low-sulphur-shipping-rules-are-affecting-global-warming/