That's the conclusion of a trio of papers published July 24 in the journals Nature and Nature Geoscience that examined the global climate over the past two millennia. The researchers showed that none of the past fluctuations — that is, not the Little Ice Age, the warm period known as the Medieval Climate Anomaly or any other famous shift — had the global reach that modern climate change is having. Past fluctuations tended to be localized, affecting primarily one region at a time. Modern climate change, by contrast, is messing with the entire world.

"Temperatures did not rise and fall everywhere in step [in the past]," editors wrote in an accompanying opinion piece in Nature Geoscience. "Specifically, early cool or warm intervals that lasted for centuries peaked at different times in different regions."

That's a radical departure from modern climate change, Scott St. George, a climate researcher at the University of Minnesota who wasn't involved in the research, wrote in a news and views article for Nature.

"Although the Little Ice Age was the coldest epoch of the past millennium, the timing of the lowest temperatures varied from place to place," St. George wrote. "Two-fifths of the planet were subjected to the coldest weather during the mid-nineteenth century, but the deepest chill occurred several centuries earlier in other regions. And even at the height of the Medieval Climate Anomaly, only 40% of Earth"s surface reached peak temperatures at the same time. Using the same metrics, global warming today is unparalleled: for 98% of the planet's surface, the warmest period of the Common Era occurred in the late twentieth century."

That means that almost every part of the planet had its hottest decades in the past 2,000 years at the same time.

And the 21st century, which is outside the scope of these papers, has been much hotter than the 20th century so far. In fact, the world is on track to keep warming as greenhouse gases continue to accumulate in the atmosphere.

To develop a rigorous picture of global temperatures over the past 2,000 years, the researchers relied on nearly 700 records from the so-called PAGES 2k proxy temperature database. That database rounds up evidence from ice cores, trees, coral and other substances that change their appearance or chemical composition based on global temperatures. The researchers used those records to build a detailed map of climate fluctuations the world over. And none of them look like the consistent, persistent shifts we're seeing today.

Of course, the causes are different, too. Evidence from the previous 2,000 years shows that short-lived volcanic events were the main drivers of climate fluctuations, the authors wrote. Human activities were perhaps a very minor secondary factor over that period. Now, humans are the ones driving the bus. And this time, it's headed toward the edge of a cliff.

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