A potent greenhouse gas and biological irritant, ozone near the Earth surface is also a health-damaging air pollutant, regulated by the U.S. Environmental Protection Agency. Climate shifts have caused Asian ozone pollution reaching Hawaii to rise unexpectedly in autumn since mid-1990s, according to this study. The findings, published in Nature Geoscience, imply that variability in airflow patterns must be considered when attributing observed ozone changes to human-induced trends in precursor emissions.