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Radio personality Hal Turner ran a segment on Aug. 8, 2019, that purported to report on an admission from NASA that climate change does not occur from human-made factors. This journalistic scoop did not come from a whistleblower or leaked documents, Turner stated, but from a 20-year-old educational feature on NASA’s publicly accessible online magazine, Earth Observatory: This story was picked up by the website Natural News, where it gained further virality. One of the more telling approaches for outlets that promote a specific brand of climate-change denial is to report as news their discovery of something that, while perhaps new to them, is fundamental to the field of climate science and in no way in conflict with the concept of anthropogenic climate change. When climate scientists discuss evidence for anthropogenic changes in the climate system, they do not simultaneously argue that there are no natural causes of variation in the climate system. Asserting that would be a straw-man argument. Evidence of natural climate variability is not evidence of a lack of human input into the climate system. That is, however, the sole premise both the Natural News and Hal Turner posts work with, per Natural News: (As an aside, 1958 was the year NASA was founded. It holds zero specific relevance to the history of Milankovitch cycles.) As accurately copied and pasted from NASA’s website, Milankovich cycles do indeed describe three periodic variations in the way the Earth rotates around the sun. Eccentricity describes the shape (how circular or oblong the path is) of Earth’s orbit around the sun. That shape varies over long periods of time between nearly a perfect circle and slightly oval-shaped orbit. The eccentricity cycle, from circular to oval and back to circular, lasts (in simplified terms) roughly 100,000 years. Another cycle, precession, describes how the orientation of Earth’s axis varies over time such that the North Pole is not always pointed at the North Star as it is today. Instead, it cycles like a slightly off-center toy top, returning to its original position every 26,000 years. The final cycle, axial tilt or obliquity, describes the angle at which Earth's axis is tilted. This angle, which is responsible for our seasons, is not fixed and ranges between 22.1 and 24.5 degrees over a cycle that lasts 41,000 years. Knowledge of these cycles, each of which affects aspects of the climate system in different ways, is immensely helpful to scientists — especially climate scientists. Combining the relative input of each of these cycles, scientists can mathematically determine how much solar energy any given part of the Earth’s surface would have received at any time going back (or forward) in time. In geologic records of past climate, the rhythm of this cycle can be seen in intricate detail such that it can be used to figure out how much time a given rock or core sample represents. This holds up even if that rock was deposited alongside dinosaurs millions of years in the past. Milankovitch cycles do not complicate the scientific observation that human-released CO2 is causing an observable net increase in global temperatures. Milankovitch cycles operate on time scales that are vastly greater — tens to hundreds of thousands of years — than the timescales at issue for anthropogenic global warming. Left to its own devices, the orbital arrangement our planet currently finds itself in would likely keep us in the current interglacial period (not a widespread ice age, not an ice-free world) we currently find ourselves in for another 50,000 years — a relatively quiet period of time from a Milankovich perspective. In other words, Milankovitch cycles cannot address rapid rises in temperatures that are currently being witnessed on human time scales — events occurring on time periods that represent a fraction of even the shortest Milankovitch cycle. The concern is what added effect humans are putting into the system on top of the more slowly varying orbital changes. The assertion that NASA is admitting anything by acknowledging the not-at-all controversial existence of Milankovitch cycles is false, and a full article alleging as such betrays nothing but an ignorance of the field such outlets claim to be exposing.
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