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Unfortunately, the Global Warming ‘Pause’ Is Perfectly Natural

Statistical analysis reveals that Earth is still cooking, despite the recent temperature plateau.
Image: NASA/Goddard

If you spend much time touring really any comment section related to really any article on global warming, you may already be painfully aware of a certain favorite climate change rebuttal. It goes something like this: "If the climate is changing, why isn't it?"

This refers to an apparent slowdown in the rise of average global temperatures seen between 1998 and 2013, an observation that, for a certain type of person predisposed to "warming!? but it's cold out!"-styled arguments, seems like the absolute most damning thing ever for the very notion of global warming if not climate science itself.

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The rest of us understand that nature remains nature, and that means the climate, however much affected by the human-sourced deluge of greenhouse gases, will be variable—even at the resolution of decades. Still, many climate scientists would probably prefer to have a firm explanation for the plateau, in terms of cause and effect.

They might find some solace in a new study from researchers at Montreal's McGill University, which, using a statistical method recently developed at the university, concludes that the recent lull is well within the boundaries of normal, natural temperature variations. More specifically, the cooling fluctuations of between 0.28 to 0.37 degrees Celsius seen since 1998 align with a cyclical variation that's occurred every 20 or 50 years through pre-industrial history, as revealed through temperature "proxies" like tree rings, ice cores, and lake sediment. Using these stand-ins, "we find many examples of these variations in pre-industrial temperature reconstructions,” said study author Shaun Lovejoy in a McGill statement.

Moreover, the recent cooling, "exactly follows a slightly larger pre-pause warming event, from 1992 to 1998,” Lovejoy continued. The warming deceleration then can be viewed as a correction of a prior acceleration; the two events are "nearly canceled," in the paper's words. The overall warming progression remains stable, and, “the pause thus has a convincing statistical explanation.”

In the paper's conclusion, Lovejoy notes that, for climate skeptics, uncertainty in the climate predictions derived from global circulation models (GCMs) makes them prime targets for "natural variability" rebuttals. "To be fully convincing, GCM-free approaches are needed: we must quantify the natural variability and reject the hypothesis that the warming is no more than a giant century-scale fluctuation," Lovejoy writes in the current paper. "With the help of nonlinear geophysics ideas on fluctuations and scaling, this has been done."

Meanwhile, there's still a vast field of study to be done exploring the reasons for these cooling periods, and one with critical implications for how the Earth responds to its new overheated state. Many accept that the leveling off of atmospheric warming seen in recent years is matched by increased warming in the planet's deep oceans. That is, global warming is progressing just as expected from greenhouse gas models, but much of it is being absorbed and masked by the enormous cooling potential of Earth's bodies of water.

This process is as yet poorly understood, owing largely to a lack of observational data on deep-ocean circulation patterns, a fact that has mostly to do with the sheer difficulty of monitoring currents at high depths for long periods of time. The sketchy factors that influence ocean heat uptake, such as latitude and cloud cover, are just now being cracked.

In any case, oceans are hardly to be taken as a global warming savior—eventually they'll warm up enough such that they lose any heat sink ability. What happens then is hard to predict, but it's certain to be very, very bad.