Plants will likely survive for a very long time. Moreover, they may very well persist even after the Sun evaporates the oceans from Earth’s surface. This is stated in a new article by two planetary scientists who used a series of models to estimate the maximum lifespan of Earth’s plant biosphere, meaning its plant life.
Their modeled scenarios, detailed in the Journal of Geophysical Research: Atmospheres, suggest that the last plant on Earth may not wither or die until 1.87 billion years have passed.
By that time, the Sun will shine about 20 percent brighter, which will likely either scorch or destroy plant life.
Nevertheless, an asterisk could be added to that statement, potentially allowing plants (and other life forms) to exist beyond that point.
Plants make up about 80 percent of all biomass on the planet, so it would be beneficial for Earth to continue providing them with ample sunlight, water, and carbon dioxide. But how long can this be sustained?
And how much time will pass before plants reach their limit?
To find out, astrobiologist Jacob Haqq-Misra and planetary climate specialist Eric Wolf from Blue Marble Space, a non-profit research institute in Seattle, ran a series of simulations.
They used a three-dimensional model to calculate what will happen to Earth’s climate over the next 2 billion years. The model was designed to account for how much brighter the Sun is predicted to become during this time, as well as changes in atmospheric carbon dioxide (CO₂) concentrations.
If human-induced CO₂ emissions are ignored, Earth’s natural carbonate-silicate cycle involves the continuous removal of CO₂ from the atmosphere into the oceans, where it gradually settles on the seafloor, turns into rock, and eventually gets released back into the atmosphere through volcanic eruptions and plate tectonics.
It is unclear how strongly this type of weathering depends on surface temperature, so the researchers modeled both strong and weak versions of the cycle.
In the intensive weathering model, Earth’s surface temperature remains relatively stable, but the amount of CO₂ in the atmosphere steadily declines. Under this scenario, plants will experience a carbon deficit, leading to the death of the plant biosphere in about 1.84 billion years.
However, in the weak weathering model, CO₂ levels remain stable, but temperatures continue to rise. Eventually, Earth’s average temperature reaches about 65 degrees Celsius, at which point land plants cannot survive.
According to this scenario, the maximum lifespan of plants on Earth will be about 1.87 billion years into the future—longer than most previous studies suggested.
“This suggests that Earth’s photosynthetic biosphere may remain viable in some form until the planet begins to lose water,” the researchers write. “If so, the maximum lifespan of Earth’s plant biosphere is comparable to the lifespan of Earth’s oceans.”
However, there is a very curious nuance in this study: these simulations were conducted without considering the evolution of plant life or any potential technological advancements made by humans (or another intelligent civilization that might emerge in the distant future).
Either of these factors, or both, could extend the lifespan of plants on Earth or, more importantly, beyond it.
“We can envision a scenario where plants develop the ability to regulate their temperature and pressure, possibly in response to climate change,” the researchers write. “As the sun grows brighter, plants might favor an aerial environment and adapt accordingly, spreading to high-altitude regions, the stratosphere, and beyond. From Earth’s upper atmosphere, life could continue to spread to low-gravity objects like comets and the Moon, as well as into free-floating space.”
Possible technological interventions sound highly speculative. Geoengineering methods, such as reflective aerosols in the upper atmosphere or orbital sunshades, could cool Earth under increasing sunlight, but the consequences of these risky strategies are not fully understood.
Even more speculative ideas include moving Earth itself to a more distant orbit or manipulating the Sun’s mass to maintain constant brightness and temperature of its solar radiation.
Of course, it is impossible to predict the future with certainty, but it is still pleasant to think that Earth might remain green for another billion years.
“Life on Earth is resilient, and the constraints imposed by heat stress or CO₂ deficiency may reflect only our observations of the biosphere today, rather than rigid limits on how the biosphere can evolve,” the researchers conclude. “We suggest that, ideally, our planet’s future will depend on whether life can persist for at least as long as Earth itself.”
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