How long can plants survive on Earth? New model suggests up to 2 billion more years

Vegetarians need not worry yet—plants will be on Earth for a long time to come. But not forever. The sun will ultimately determine the long-term existence of life on Earth. Its total energy output, called luminosity, has been increasing over epochs and eons by about 10% every billion years—determining much of Earth’s surface temperature. This will continue for billions of years in the future.

The greenhouse effect is the second-largest influence on temperature, determined largely by the concentration of carbon dioxide (CO₂) in the atmosphere. Its future is less certain, and that has implications for the long-term survival of plants.

CO₂ is naturally removed from the atmosphere by silicate weathering—a chemical reaction of rocks, rainfall and CO₂ that creates calcium and bicarbonate, which ultimately drain down rivers and settle on the bottom of the ocean as calcium carbonate.

Through the geologic cycle, this carbon ultimately reappears in the atmosphere via volcanic eruptions. At present, about 130 million tons of carbon is removed by silicate weathering every year, while humans now emit about 90 times that amount.

In a new paper published in Journal of Geophysical Research: Atmospheres, Jacob Haqq‐Misra and Eric Wolf of Blue Marble Space in Seattle determined the future of plants by looking at the long-term future of solar luminosity and CO₂ levels in the atmosphere, using a three-dimensional general circulation climate model and considering whether future silicate weathering will be strong or weak.

The research required looking at the three broad classes of plants, depending on how they photosynthesize sunlight: C3 plants, C4 plants and CAM photosynthesis plants. Their relative vegetation abundances on Earth, by number of species, are about 95%, 3% and 2%, respectively. Each has a different CO₂ starvation limit: C3 plants fail below about 50 parts per million (ppm) CO₂ in the atmosphere, C4 plants fail below about 10 ppm, and CAM species even lower.

When will these CO₂ values occur? The silicate weathering rate depends on temperature. How do these 3-D model results compare to earlier, simpler models?

Weak silicate weathering

In this scenario, the researchers considered the future sun’s increasing insolation while Earth’s atmospheric CO₂ was set at an initial point. The rate of silicate weathering was assumed to be weak.

As the sun brightens, causing the temperature to warm, the silicate weathering rate increases only slightly, and as a result, CO₂ levels in the atmosphere do not drop much and remain approximately constant compared with today’s value.

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

Their result shows ample habitability with slowly increasing temperatures up to about 1.5 billion years from now, followed by significant warming up to 2 billion years. By then, surface habitability peters out, with no regions left of complex habitability such as plants. Earth would come to be dominated by microbes.

Strong silicate weathering

Here, the researchers held the surface temperature constant at today’s value of 288 Kelvin and assumed future silicate weathering would be strong compared with today. The sun’s luminosity increases by 20% over 2 billion years, so the CO₂ level decreases as it is plucked out of the atmosphere by strong weathering. This reduces the greenhouse effect, so surface temperatures tumble.

What does all this mean for plants? This framing was used with their specialized three-dimensional climate model called Exo-CAM, which was developed by the authors with others in 2022 to consider diverse exoplanets, handling a wide range of atmospheric compositions, including in Earth’s deep past and its deep future.

Their model, the most advanced, found that the vegetative biosphere could persist much longer—1.35 billion to 1.86 billion years—than previously estimated, depending on the weathering regime.

“We find that life on Earth would survive at least until the brightening sun evaporates our oceans, almost 2 billion years from now,” Haqq‐Misra said. “And even then, life may find a way to leave Earth and continue thriving beyond,” through technology such as orbital sunshades or long evolutionary processes. Sunscreen will likely be involved.

Who’s behind this story?

David Appell

David Appell is an Oregon-based freelance science writer whose work has appeared in Scientific American, New Scientist, Physics World, and The Washington Post. He holds a Ph.D. in physics from Stony Brook University.

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Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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