Earth’s Plants May Have Nearly 2 Billion Years Left Before the Planet Becomes Too Hostile

New simulations extend the future of Earth’s plant life by hundreds of millions of years.

Earth’s last great survivor may not be humanity, or even animals. It may be photosynthesis itself. Cacti, some algae, and aquatic plants are built to handle conditions far harsher than those most life on Earth faces today.

A new three-dimensional climate study extends the life expectancy of Earth’s plant biosphere to about 1.8 billion years from now, hundreds of millions of years beyond many earlier forecasts.

The finding gives our planet a longer biological future than expected and reframes the search for life elsewhere: planets around aging brighter stars may still carry detectable life long after they stop looking habitable.

A Growing Sun

The sun brightens as it ages, increasing its energy output by about 10% every billion years. Long before it expands into a red giant and swallows Earth roughly 5 billion years from now, that extra sunlight will strain the planet’s climate. At some point, billions of years into the future, life will become unbearable.

But heat is only half the problem.

Carbon dioxide is like Earth’s deep-time thermostat. Rainwater reacts with silicate rocks, pulling CO2 from the air and eventually locking it away as carbonate on the seafloor—a process known as silicate weathering. Volcanoes eventually return some of that carbon to the atmosphere, completing a slow geologic cycle.

“The thermostat on the planet is the greenhouse effect: it keeps the amount of CO2 in balance to roughly keep Earth’s temperature in a nice habitable range,” Jacob Haqq-Misra of Blue Marble Space told New Scientist.

For billions of years, that thermostat helped keep Earth livable. In the far future, it could become a problem for plants.

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As the sun brightens, stronger weathering could pull more CO2 from the atmosphere. That would cool the planet, but it would also remove the raw material plants need for photosynthesis. If weathering proves weaker, CO2 may remain more abundant, but temperatures could rise until plants can no longer tolerate the heat.

Either way, Earth’s future vegetation faces a squeeze: too much heat on one side, too little carbon dioxide on the other.

Earlier models often placed the end of the large photosynthetic biosphere within about one billion years from now or sooner. Haqq-Misra and Eric Wolf revisited the question with a three-dimensional climate model, which can track features simpler models miss, including clouds, rainfall, ice and regional temperature differences.

Their answer gives plants more time. In their new study, Earth’s vegetative biosphere lasts about 1.35 billion to 1.86 billion more years, depending on how strongly weathering responds to warming and how little CO2 the toughest photosynthetic organisms can survive on.

Two Possible Futures

The researchers examined two extreme future scenarios.

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In one, weathering stays weak. CO2 remains near modern levels, but the planet heats up. Their model found that most land plants cross dangerous heat limits around 1.68 billion years from now. The toughest land plants could persist until about 1.87 billion years.

In the strong-weathering scenario, Earth avoids the worst heat because rock weathering keeps drawing CO2 out of the air. But that creates a different threat. Plants need CO2 to photosynthesize, and earlier studies often treated 10 parts per million as the point where even hardy C4 plants — grasses, corn and sugar cane among them — could no longer support a large plant biosphere. In Haqq-Misra and Wolf’s model, Earth reaches that threshold about 1.35 billion years from now.

CAM plants—like cacti, pineapple, and agave—are unusually efficient at gathering carbon, and some aquatic plants and algae can draw on bicarbonate dissolved in water. With a cutoff of 1 part per million, the scientists’ model lets a stripped-down photosynthetic biosphere survive until about 1.84 billion years from now.

“Life on Earth is incredibly adaptive,” Haqq-Misra said in a statement. “Even hot and low CO2 environments can allow plant life (as well as the animals that eat them) to survive for a long time.”

Way More Resilient Than We Thought

None of this makes the far-future Earth sound welcoming. A planet with a surviving photosynthetic biosphere would not be a planet with today’s forests, farms or coral reefs. As heat rises or CO2 falls, familiar ecosystems would disappear. The holdouts would probably live where conditions remain tolerable longest: near the poles, in water, in deserts, or perhaps in protected habitats built by a future civilization.

That is why the study’s long timeline needs a careful reading. Haqq-Misra and Wolf are not saying Earth will stay green in any familiar sense. They are saying the basic engine of photosynthesis may keep running after much of the living world has thinned out.

The larger point reaches beyond Earth. Astronomers often judge distant planets by how long they may remain habitable as their stars age. If photosynthetic life can persist here for nearly 2 billion more years, then older planets around other stars may deserve a closer look. Some may be past their prime and still alive.

Ultimately, the sun will engulf Earth, and at that point, all bets are off. But at least the new work suggests that photosynthetic life could persist longer than expected, lasting almost until Earth starts to lose its oceans.

The study was published in the Journal of Geophysical Research: Atmospheres.