At least 74% of the climate warming observed since the mid-twentieth century is extremely likely to be caused by human activities, according to a study published online this week in Nature Geoscience. The results confirm earlier findings using independent and complementary methodology. Reto Knutti and Markus Huber estimated the human contribution to the observed warming in the second half of the twentieth century, based on an assessment of the Earth’s energy balance. They find that since 1950, greenhouse gas emissions have led to a temperature increase of about 0.85 °C. Over the same period, aerosols cooled the Earth by about half that amount. Earlier attributions of temperature increases to human action relied on the ability of climate models to accurately simulate spatial and temporal warming patterns from different causes. The new results are not based on this assumption, and therefore substantially raise confidence in the importance of human-induced causes of the recent temperature rise.