The Washington Post recently published an article about a scientific effort to understand the Earth’s climate over the past 485 million years. The study has revealed a history of wild shifts and far hotter temperatures than scientists previously realized. The study, published in the journal Science, is the most rigorous reconstruction of Earth’s past temperatures ever produced and reveals that the world was in a much warmer state for most of the history of complex animal life on Earth. At its hottest the Earth’s average temperature reached 96.8 degrees Fahrenheit (36 degrees Celsius) — far higher than the recent historic 58.96 F (14.98 C) in humanity’s existence.
The timeline illustrates how swift and dramatic temperature shifts were associated with many of the world’s worst moments — including a mass extinction 251 MYA that wiped out roughly 90 percent of all species and the asteroid strike 65 MYA that killed the dinosaurs. The timeline encompasses almost all of the Phanerozoic — the geologic eon that began with the emergence of multicellular, non-microscopic organisms and continues today. It portrays a global climate that was more dynamic and extreme than researchers had imagined and, in keeping with decades of past research on climate, the chart hews closely to estimates of carbon dioxide in the atmosphere, with temperatures rising in proportion to concentrations of the heat-trapping gas.
The study also makes clear that the conditions humans are accustomed to are quite different from those that have dominated our planet’s history. For most of the Phanerozoic, the research suggests, average temperatures have exceeded 71.6 F (22 C), with little or no ice at the poles. Coldhouse climates — including our current one — prevailed just 13 percent of the time. One of the more sobering revelations of the research is that life on Earth has endured climates far hotter than the one people are now creating through planet-warming emissions. But humans evolved during the coldest epoch of the Phanerozoic, when global average temperatures were as low as 51.8 F (11 C).
The new temperature timeline raises questions as as well as answers, though it is considered more accurate than other estimates. The timeline was assembled through a technique called data assimilation, which combines real-world evidence from 150,000 oceanic data points with climate models to yield more rigorous and accurate results. But it’s also possible that the data assimilation assumes too much warming and is missing factors that might forestall a runaway greenhouse effect.
For the billions of people who are now living through the hottest years ever recorded — and facing a hotter future still — the timeline should serve as a wake-up call. Even under the worst-case scenarios, human-caused warming will not push the Earth beyond the bounds of habitability. But it will create conditions unlike anything seen in the 300,000 years our species has existed — conditions that could wreak havoc through ecosystems and communities. As Emily Judd, a researcher at University of Arizona and the Smithsonian specializing in ancient climates and the lead author of the study said, “As long as one or two organisms survive, there will always be life. I’m not concerned about that. My concern is what human life looks like. What it means to survive.”