Australia suffered its worst wildfire season ever in 2019-2020. The flames burned 126,000km2 of land but the smoke had a much wider impact. Scientists say it cooled the ocean thousands of miles away, sparking a rare 3-year La Niña climate event. La Niña is caused by cooler-than-average waters in the Pacific Ocean. This usually happens once every 3-5 years and it can affect weather and climate patterns around the world.