Why this warmer world is not just a passing phase

In the late 1990s, three scientists published a paper charting the Earth’s temperatures over the last millennium. For the first 900 years, the trend line was the definition of boring: just little blips up and down. That changed around 1900, when the mean global temperature shot up, and kept rising.

That now-famous trend line, dubbed “the hockey stick” because of its sharp upward slope, is so vivid that it has played a key role in two decades of argument over whether the Earth’s atmosphere is warming, and whether those changes are caused by heat-trapping gases generated by human activities. 

It’s not hard to pick apart a single study’s data. Critics of the hockey stick pointed to centuries-long temperature shifts such as the Medieval Climate Anomaly and the Little Ice Age to argue that anomalies in the 20th century were also short-term, natural shifts. Critics also noted the patchwork nature of the pre-1900 data, which didn’t rely on direct measurements, and said there was no direct evidence that increased greenhouse gas emissions from the burning of fossil fuels was causing the current temperature rise.

Uncertainty is central to the enterprise of science. It’s a rare day when a single study — or dozens, or hundreds — answers a question without a doubt. And because uncertainty almost always remains, scientists have to explain both quantitatively and qualitatively how uncertain they are. That’s good science. But climate change naysayers used that uncertainty to say, “The scientists aren’t sure.” And it meant that when we journalists reported accurately on the science by noting uncertainty, we gave more ammunition to doubters.

Well, scientists are now sure. In 2013, the Intergovernmental Panel on Climate Change, an international consortium convened by the United Nations to evaluate the science of climate, released a report saying there was greater than 95 percent certainty that the substantial warming was due to human activities. And scientists are increasingly linking extreme weather events worldwide, from heat waves to hurricanes, to human-caused climate change (SN: 1/19/19, p. 7).

In this issue, we report on how the city of Boston is regularly flooding due to rising sea levels. Freelancer Mary Caperton Morton explains how policy makers and scientists are racing to develop responses to keep the venerable city functioning as the water moves inland. And earth and climate writer Carolyn Gramling reports on a startling new study that lays to rest the argument that the warming we’re experiencing is just another normal climate shift. This one is clearly different, the data show: Those earlier temperature fluctuations were regional; what’s happening now is worldwide. 

Michael Mann, a climate scientist at Penn State who is one of the researchers who developed the hockey stick data chart, said back in 2005 that he thought that people wouldn’t take climate change seriously until they saw it in their own backyards. People in Boston think they’re seeing it, as do people in many other communities around the world who are bracing for more extreme heat, rainfall, drought and storms. Our charge at Science News is to continue to report on the science while chronicling humankind’s responses, for good or ill.