It was one of the biggest climate change questions of the early 2000s: Did the planet’s rising fever stop, even as humans pumped more heat-trapping gases into Earth’s atmosphere?
By the turn of the century, the scientific understanding of climate change was solidified. Decades of research showed that carbon dioxide was accumulating in Earth’s atmosphere, thanks to human activities such as burning fossil fuels and cutting down carbon-storing forests, and that global temperatures were rising as a result. Yet weather records show that global warming slowed between 1998 and 2012. How is this possible?
After careful study, the scientists found the apparent break to be a hiccup in the data. The Earth, in fact, continued to warm. However, this hiccup prompted an outsized backlash from climate skeptics and scientists. It serves as a case study of how public perception shapes science, for better or worse.
The mystery of what came to be called the “global warming gap” arose when scientists produced year-to-year data on the planet’s average surface temperature. Many organizations maintain their own temperature datasets; Each relies on observations gathered at weather stations and from ships and boats around the world. The actual amount of warming varies from year to year, but overall the trend is increasing, and record-warm years are becoming more common. For example, the 1995 Intergovernmental Panel on Climate Change report noted that recent years have been the warmest recorded since 1860.
And then came the mighty El Nio of 1997–1998, a weather pattern that transferred large amounts of heat from the ocean into the atmosphere. The planet’s temperature rose as a result – but then, according to weather records, it decreased dramatically. Between 1998 and 2012, global average surface temperatures increased by less than half the rate between 1951 and 2012. It had no meaning. Global warming should accelerate over time as people increase the rate at which they add heat-trapping gases to the atmosphere.
By the mid-2000s, climate skeptics had captured the narrative that “global warming has stopped.” Most professional climate scientists were not studying this phenomenon, as most believed that the apparent break was within the limits of natural temperature variability. But public attention soon turned to them, and researchers began investigating whether the pause was a real thing. It was a high-profile shift in scientific focus.
“In studying that odd period, we learned a lot of lessons about both the climate system and the scientific process,” says Zeke Hausfader, a climate scientist with the technology company Stripe.
By the early 2010s, scientists were busy explaining why the global temperature record seemed flat. Ideas included the contribution of cooling sulfur particles emitted by coal-burning power plants and the heat being carried by the Atlantic and Southern Oceans. Such studies were by far the most focused effort to understand the factors driving year-to-year temperature variability. They revealed how much natural variability can be expected when factors such as a powerful El Nio are superimposed on a long-term warming trend.
Scientists spent years investigating alleged warming pauses – devoting more time and resources to them than they might otherwise have. So many papers were published on apparent pause that scientists began to joke that the journal nature climate change it should be renamed nature gap,
Then in 2015, a team led by researchers from the US National Oceanic and Atmospheric Administration published jaw-dropping findings in the journal Science, The rise in global temperatures had not stopped; Rather, incomplete data had obscured ongoing global warming. When more Arctic temperature records were included and biases in ocean temperature data were corrected, the NOAA dataset continued to warm. With the newly revised figures, the apparent pause in global warming disappeared. A 2017 study led by Hausfather confirmed and expanded on these findings, like other reports.
Even after these studies were published, the gap remained a favorite topic among climate skeptics, who used it to argue that the concern over global warming was high. Congressman Lamar Smith, a Republican from Texas who chaired the Science Committee of the House of Representatives in mid-2010, was particularly outraged by the 2015 NOAA study. He sought to look at the underlying data, accusing NOAA of changing it. (The agency denies data manipulation.)
“In retrospect, it’s clear that we focused too much on the obvious gaps,” Hausfather says. Figuring out why global temperature records seemed to plateau between 1998 and 2012 – but it’s important to have a bigger picture about a broader understanding of climate change. Hiccups represent a small uptick in a much longer and much more important trend.
Science relies on testing hypotheses and questioning conclusions, but here is one case where investigating an anomaly was arguably taken too far. This led the researchers to doubt their findings and question their well-established methods, spending a large amount of time, says Stephan Lewandowski, a cognitive scientist at the University of Bristol who has studied climate scientists’ response to lag. Scientists studying the gaps could work instead to provide policy makers with a clear understanding of the reality of global warming and the urgency of addressing it.
The debate over whether the gap was real has led to public confusion and undermined efforts to persuade people to take aggressive action to mitigate the effects of climate change. It’s an important lesson moving forward, Lewandowski says.
“My understanding is that the scientific community has moved on,” he says. In contrast, the political operatives behind organized denial have learned a different lesson, which is that the ‘global warming has stopped’ meme is very effective at generating public complacency, and so they will use it at every opportunity. “
Already, some climate denials are talking about a new “pause” in global warming because not every one of the past five years has set a new record, he noted. Yet the big picture trend is clear: Global temperatures have continued to rise in recent years. The warmest seven years on record have been since 2015, and each decade since 1980 has been warmer than the one before.
