The science news media has a pretty simple job: Find facts, and report them. Typically, this entails reading a scientific study, talking to the study’s authors and outside experts, writing, and fact-checking the confusing bits with experts again. But sometimes, the narrative the media wants isn’t actually supported by the study, or the experts. Such is the case with a new paper on climate change.
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The study, published in Nature Geoscience earlier this week, took a stab at trying to figure how much carbon humans can emit before crossing the 1.5 C global warming threshold set forth in the Paris Climate Agreement. And it came to a sort of optimistic conclusion: We may have more carbon in the bank than we thought. Other experts were immediately sceptical, but that didn’t stop several outlets from running stories that twisted the study’s key conclusion into a bad parody of itself, suggesting that the “fear of global warming is exaggerated,” and climate change may not be “as threatening as previously thought.”
Things went totally off the rails from there. “The scientists who produce those doomsday reports for the Intergovernmental Panel on Climate Change have finally come clean — the computer models they have been using to predict runaway global warming are wrong,” bloviated The Sun. “Climate alarmists have finally admitted that they have got it wrong on global warming,” Breitbart piled on.
It got so out of hand that the University of Oxford-based researchers released a statement yesterday disavowing the idea that we now longer need to take aggressive action to reduce carbon emissions, followed by a response article in The Guardian this morning.
Here’s what really happened. The researchers made assumptions about how much global warming has already occurred, and then used models to project that future carbon emissions of up to about 900 billion tons of CO2 could be compatible with limiting the warming to 1.5 C this century. That’s equivalent to about 20 more years of CO2 emissions at current rates. Contrast that with other estimates of the remaining carbon budget derived from the Intergovernmental Panel on Climate Change, which suggest we have maybe four years before we’re locked into at least 1.5 degrees of warming, and it sounds somewhat promising.
Somewhat. “Our analysis suggests that ‘pursuing efforts to limit the temperature increase to 1.5 C’ is not chasing a geophysical impossibility, but is likely to require a significant strengthening of the NDCs at the first opportunity in 2020,” the researchers write. In other words, countries still have to ratchet up their ambitions a lot in order to limit warming to 1.5 degrees — aggressive emissions reductions would need to start today, and our CO2 output would need to be brought to net zero in about forty years at most.
Other climate scientists pushed back against the new study’s estimate, saying that the ‘pre-industrial baseline’ period the authors use to figure how much warming has already occurred — temperature data from the UK’s Met Office spanning 1861 to 1880 — is misleading. There’s an ongoing debate as to how these baseline temperatures are defined, but as climatologist Zeke Hausfather points out at Carbon Brief, other global temperature records that go back as far would have yielded more warming by 2015 — and hence less carbon in the bank.
Whether the authors are correct in their baseline or not, the study’s message isn’t that it’s time to rest on our laurels if we want to limit global warming to 1.5 degrees. But that misleading message was compounded when some outlets keyed in on a suggestion in the paper that climate models have “overestimated” warming by 0.3 degrees C, taking this to mean that temperatures are not rising as quickly as the IPCC says they are. Not only was the paper was not intended to assess discrepancies between climate models and observations, its findings are in line with the IPCC, a fact which the authors readily admit.
“Out predictions for warming rates over the coming decades are identical to those of the IPCC,” study authors Miles Allen and Richard Miller wrote in the Guardian.
Comparing models with observations isn’t always an easy or even a good thing to do. For instance, while some models (including those in the paper) estimate air temperatures over the planet’s surface, scientists measure Earth’s temperature in both the air and the surface oceans, which have been warming more slowly. “Studies that account for both the land/ocean sampling issues and the needed corrections for historical forcings show no discrepancy between observed vs. modelled warming,” Penn State climate scientist Michael Mann told Gizmodo.
All of which is to say: climate science is hard, and you get different answers about the future based on what assumptions you make about the past and what models you choose to look at. These differences are amplified when we’re trying to understand small changes over the short term, which can lead to some wildly varying conclusions about what sorts of carbon policies are appropriate for hitting specific, and specifically low, global warming targets.
Still, the essential conclusion of this new study didn’t differ all that much from those that came before it: We need aggressive carbon reductions immediately if we want to keep climate change to a minimum.