Earth is locked into 5 degrees Celsius of global warming? Not so fast.
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A recent climate study implied that Earth was 'locked into' 5 Celsius degrees of warming, but experts say that forecast is off-base
On Tuesday, a new climate study sent media outlets into a frenzy. News articles declared that Earth was "locked into" 5 Celsius degrees of warming – an exceptionally dire forecast, since most climate scientists warn that a boost of just 2 degrees C. would be catastrophic.
But fortunately for coral reefs and coastal communities, scientists now say that prediction was wrong.
It was Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, who led the charge. Dr. Schmidt was perhaps the most vocal of a group of prominent dissenters, all of whom insist that the actual committed warming estimate hovers around 0.5-1 degrees C. That number, while still significant in terms of global effects, is a far cry from the initial findings. So what caused the discrepancy: bad science or bad science journalism?
The original study, which was published in the journal Nature, assembled a 2-million-year temperature record to predict future rises in heat. That data was based on the composition of ocean sediment cores, which can be used to estimate atmospheric conditions and temperature at certain points throughout the planet’s history.
Lead author Carolyn Snyder, who is a climate policy official at the Environmental Protection Agency, used the data to draw historical correlations between changes in temperature and carbon dioxide levels. But in her study, Dr. Snyder also made a prediction: that if past relationships between temperature and CO2 hold true today, we would have irreversibly committed to about 5 degrees of warming.
But that logic is fundamentally wrong, Schmidt tells The Christian Science Monitor. Climate warming isn’t driven by solely carbon dioxide emissions, he says, but by a slew of complex variables. Snyder’s prediction failed to consider factors such as orbital forcing – slow changes in the tilt of the Earth’s axis and the shape of its orbit that can cause ice age cycles by reducing sunlight to certain parts of the globe.
Snyder has said that the prediction was meant to provide context to historical data, not to provide an accurate prediction of future climates.
“This research cannot and does not provide a forecast or prediction for future climate change,” Snyder told Gizmodo. “All we can say is, if we take the past relationship [between temperature and CO2] and translate it forward, this is what we get.”
In many ways, the accuracy of Snyder’s prediction doesn’t have much bearing on the usefulness of the study. Previously, the most extensive temperature reconstruction only dated back 22,000 years. Schmidt himself calls the reconstruction a “step forward” – a foundation from which other climatologists can build.
So how did Synder’s prediction go from minor aside to headline-grabber?
The answer may be found in the way news outlets report on science. Most journalists, even those who do specialize in science, don’t have degrees in the scientific disciplines. Without key background knowledge, many of them base their stories heavily on press releases. Nature’s original press release for the story played up the significance of the prediction, so some news outlets followed suit.
“There was an error in the study, and that made it into the abstract and the press release that Nature put out,” Schmidt says. “Many journalists took the time to check out this extraordinary claim with independent experts – not just me – and realized that this was problematic. Some of the coverage reflected that. However the net effect in the media is one of confusion.”
Embargoed studies and press releases play a prominent role in the reporting of scientific discovery, and that dynamic has been criticized in recent years. But there’s one way for journalists to prevent confusion in communicating science: talk to as many experts as possible. Scientists have always relied on the voices of other scientists – experiments must be reproduced before they are considered viable, and studies must be peer-reviewed before they are published.
Good science journalism relies on outside perspective, too. The process of seeking out different voices can save news outlets from embarrassing mistakes and spare readers misleading information.
“The bottom line for journalists is that peer review is not infallible, and that really surprising results need to be looked at very carefully,” Schmidt says. “There are many scientists who can be tapped for comment on such findings and more journalists need to do this. And yes, sometimes they have to use their judgement to decide on what, or who, is credible.”