The unintentional consequence of lowering sulphur content in marine fuel, as part of clean air regulations, is a weakened cooling effect caused by sulphur particles in ships' exhaust fumes, according to a new model. This inadvertently exacerbates warming, potentially raising global temperatures by 0.05C by 2050. Other factors, including an underwater volcano eruption, Saharan dust absence, and El Niño, are also contributing to the ongoing ocean heatwave.