Over the last 150 years, nearly the entire Earth has experienced warming, a consistency not seen in the past two millennia, researchers reported yesterday (July 24) in Nature. Prior climate change events, such as the Little Ice Age of the 16th to 19th centuries, were regional, rather than global as is now occurring.
“Traditionally, the understanding of climate over [the past 2,000 years] is that there were globally coherent periods of climate variability—that there was a cold period called the Little Ice Age, [or] that there was a warm period called the Medieval Climate Anomaly,” coauthor Nathan Steiger, a research scientist at Columbia University, told reporters at a press conference, according to The Atlantic. “What we show is that these periods weren’t globally coherent, as previously thought.
Steiger and his team used hundreds of datasets from proxies of climate, such as tree rings and ice cores, to rebuild the environment of the past. They found no even, global shifts—either warm or cold—before the industrial era. The Medieval Climate Anomaly, for instance, was a warming phase in parts of Europe and North America in the 11th century, but South America warmed up hundreds of years later and in the eastern and central Pacific Ocean, warming occurred several centuries earlier, Science News reports.
“By contrast, we find that the warmest period of the past two millennia occurred during the twentieth century for more than 98 per cent of the globe,” the authors write in their report. “This provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures, but also unprecedented in spatial consistency within the context of the past 2,000 years.”
Climate change deniers have used past climate change events to promote the idea that current warming trends are part of cycles not driven by human activities. Mark Maslin, a climate scientist at University College London who was not part of this work, tells The Independent that the new study contradicts such erroneous thinking. “This paper shows the truly stark difference between regional and localised changes in climate of the past and the truly global effect of anthropogenic greenhouse emissions.”
Kerry Grens is a senior editor and the news director of The Scientist. Email her at firstname.lastname@example.org.