Around 1900, a respected Swedish scientist named Svante Arrhenius published a series of papers and a book that included a crazy-sounding prediction. He and a colleague were studying the carbon cycle by estimating the changes in carbon dioxide (or CO2) produced by natural processes such as rock weathering, volcanic eruptions, and ocean absorption.
He also looked at a source no one had thought of before—humans. Was it possible that humans could change the climate? Arrhenius took his colleague's calculations of carbon emissions from human activities and crunched the numbers.
When atmospheric carbon doubled, he figured, it would be enough to raise Earth's temperature 9-11°F (5-6°C), but it would take thousands of years to do it at 1896 rates. By the time his book on the subject was published in 1908, so much more coal was being burned, Arrhenius revised his estimate to centuries. But he reasoned that a warmer climate would be a GOOD thing—understandable, perhaps, given his home in Stockholm, a few hundred miles shy of the Arctic Circle.
Although Arrhenius went on to win the Nobel Prize for Chemistry in 1903, his carbon calculations faded into obscurity. In the hundred years since Arrhenius made his estimate—remarkably close to today's best figure—scientists hotly debated the causes of past and current climate change. However today, most climate scientists agree that multiple lines of evidence clearly show that human-induced climate change is taking place.