Authors say a study that looked at the rise in extreme rain and snowfall in the Northern Hemisphere in the last half of the 20th century is the first to show a link to global warming. The work builds on previous research that established broad trends in extreme precipitation events over the 20th century. Those studies suggested a link between climate change and heavy precipitation, based on the atmosphere's ability to hold more moisture as it warms. But, according to the research team that conducted the new study, those studies stopped short of presenting evidence for a direct link between human-triggered global warming and extreme precipitation.