When a heat wave roared the western United States this week, temperatures in the Death Valley in California would blow 130 degrees Fahrenheit, marking the hottest temperature measured anywhere on earth since 1931 and the third hottest day ever on our planet, period.
But Earth has seen warmer days in its past and it will experience them again in the future. During so-called greenhouse periods, when the atmosphere with greenhouse gases was too much, the planet was much warmer than today and the worst hot waves were corresponding nightmares. And although human carbon emissions have not yet propelled the Earth into a new greenhouse state, climate change is making heat waves more frequent and severe, meaning that Death Valley extreme temperatures are unlikely to last long. Earth will soon not always be as burning and uninhabitable as Venus – temperatures there are high enough to melt lead – but heat that challenges the limits of human tolerance will occur more often than the century carries, scientists say.
And in the very, very distant future, Earth could actually become like Venus.
It’s all over
It may not feel like it if you currently live in California or Japan, but Earth is currently in what geologists consider an ice house climate: a period cold enough to support an ice age cycle in which large continental ice sheets wake up and wobble close to the pulse. (Currently, the one in the northern hemisphere has retreated to Greenland.) To get a glimpse of what a much warmer world looks like, we need to go back at least 50 million years to the early Eocene.
“That was kind of the last very hot climate that the Earth experienced,” he says Jessica Tierney, a paleoclimatologist at the University of Arizona.
Today, the average temperature of the earth is about 60 degrees Fahrenheit. In the early Eocene it was closer to 70 degrees and the world was a different place. The poles were free of ice; the tropical oceans sat at spa-like temperatures of 95 degrees Fahrenheit. Palm trees and crocodiles hung out in the Arctic. Several million years earlier, at the Paleocene-Eocene Thermal Maximum (PETM), things were even warmer.
More extreme greenhouse periods drag on into the deeper recessions of geological time. During the Cretaceous Hot Hothouse 92 million years ago, surface temperatures worldwide rose to about 85 degrees Fahrenheit and remained hot for millions of years, allowing moderate rainforests to flourish at the South Pole. Some 250 million years ago, the boundary between the Permian and the Triassic period was marked by extreme global warming, where the average temperature of the Earth flirted with 90 degrees Fahrenheit millions of years ago, according to a preliminary reconstruction of the Smithsonian Institution.
In that hellish interval, Earth experienced the worst death-off of life in its history. The tropical oceans were like a hot tub. We do not have daily weather data from the Permian (like another ancient chapter in the history of the earth), but it is likely that in the large, dry interior of the supercontinent Pangea this heat wave Death Valley this week just another day would have been.
“The warmer these average conditions are, the more often you will see really extreme warming events,” Tierney says. On the hottest days in the hottest times, “places like a desert would just be unbelievably hot.”
The warmer future
All of the Earth’s recent greenhouse periods seem to have one thing in common: They were preceded by a massive pulse of greenhouse gases in the atmosphere, whether these were volcanic eruptions, which bubbled carbon dioxide or methane under the sea floor. Humans today are doing a similar planetary experiment by burning enormous fossil carbon reserves, increasing atmospheric carbon dioxide at an unexpected rate since the extinction of dinosaurs, 65 million years ago, and perhaps far earlier.
‘Mostly when we see a rapid change in climate [in the past], it is driven by similar mechanisms as what we do today, ”says MIT earth scientist Kristin Bergmann. “There is a fairly rapid change in the greenhouse gases that are warming our planet.”
As in the past, global average temperatures are rising faster again. And extremely hot days are also on the uptick, with study after study concluding that recent record temperatures would have been almost impossible without our influence.
It is difficult to predict exactly how hot Earth could become if we keep carbon in the atmosphere, experts say. As Michael Wehner, an extreme weather researcher at Lawrence Berkeley National Laboratory, put it in an email: “The increase in temperatures of future heat waves depends a lot on how far into the future and how much more carbon dioxide we emit.”
But recent research by Wehner and his colleagues provides a look at what the hot waves of tomorrow could look like if we did not limit our carbon emissions at all: By the end of the century, hot waves in California could peak at temperatures above 10 to 14 degrees Fahrenheit. higher than they do today.
That once saw Century temperature Death Valley this week? “I would expect an event of the same rarity as the 130F of today to be around 140F in that high-emission future,” Wehner says.
A Venus-like fate?
If you are a nihilist, you may point out that this is all peanuts compared to what Earth is likely to experience in the distant future. Planetary scientists have long predicted that as the sun grows older and brighter, the earth’s surface will eventually heat up to the point where the oceans begin to boil like water on a stove. Water vapor, a potential greenhouse gas, will throw into the atmosphere, triggering a running glass effect that in a billion years could transform our world into something other than our neighbor, Venus. There, under a thick, toxic and sulfurous atmosphere, surface temperatures are close to 900F.
“The assumption has been as the sun continues to rise, the same thing will happen on Earth,” says North Carolina State University planetary scientist Paul Byrne, added that billions of years ago, our planetary neighbor might have had a pleasant climate and oceans.
Venus may not have been completely destroyed by the sun. Recent model work suggests that the culprit was a series of volcanic paroxysms that “caused biblical releases of CO2 into the atmosphere, ”says Byrne. But both scenarios – planetary heat death by the sun or by volcanoes – point to a way in which events far beyond our control could send the Earth’s future climate into a harrowing hot tailspin.
“Whether it will be exactly 475 degrees Celsius now, I do not know,” Byrne says, referring to the temperature on the surface of Venus. But when Earth goes through a Venus-like transition, “it will be really, really hot.”
Even if our Blue Marble manages to escape the fate of Venus, there will be no shortage in about five billion years. At that moment, the sun will expand into a red giant star, which the Earth has undergone in a fierce fire.
“The prevailing view is that the sunny earth will wander earth,” Byrne says. ‘We get [expletive deleted]. ”
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