Global warming is typically thought of as a gradual process, but a report released this week by the U.S. National Academy of Sciences warns that greenhouse gases and other atmospheric pollutants could cause massive, sudden, and potentially disastrous climate shifts. The authors of the report relied on paleontological evidence, the historical record, and computer modeling to demonstrate that in the past, gradual climate change was punctuated by sudden temperature increases. For example, the report concluded that roughly half of the warming that has taken place in the northern Atlantic Ocean since the last ice age occurred in just one decade, triggering floods and droughts across the globe.