The latest research shows that, in the absence of severe external intervention, plants on the earth may survive nearly twice as long as previously predicted, and the earth can "remain green" for close to 1.9 billion years. The results come from two researchers at Blue Marble Space, who used climate models to assess the long-term impact of future increases in solar radiation and changes in atmospheric carbon dioxide concentrations on the fate of Earth's vegetation.
Previously, the scientific community has given widely varying estimates of when Earth's plants will end: some studies believe that vegetation may be unable to maintain its status quo due to environmental degradation in about 100 million years; other models point out that plants may still be able to persist for about 1 billion years. The latest paper published in "JGR Atmospheres" pushes this time limit further, believing that under certain scenarios, the last patch of green on the earth may not completely disappear until about 1.87 billion years ago.
The research team focused on examining two possible development paths: one assumes that atmospheric carbon dioxide concentration generally remains near current levels, while surface temperatures slowly increase with increased solar radiation; the other assumes that atmospheric carbon dioxide will continue to decline in the next billions of years due to accelerated "washing" of carbon elements by geological processes such as weathering. They used climate models to conduct deductions at different points in time to measure how long vegetation could maintain in an environment that gradually warmed and gradually became "carbon deficient".
Under the scenario where temperature rise is the dominant factor, the model shows that the global average temperature will slowly rise by about 20 degrees Celsius in about 1.5 billion years. After about 500 million years, the warming will further accelerate, adding an additional 40 degrees Celsius. This long-term high temperature will make the surface environment more and more harsh on plants. Eventually, even the most tolerant species will have difficulty surviving. Research estimates that plant communities will completely disappear about 1.87 billion years ago.
If we start from another path, assuming that geological and climatic processes accelerate the removal of carbon dioxide from the atmosphere, the main limiting factor facing plants will shift from "heat" to "hunger". In such models, atmospheric carbon dioxide concentrations could fall from just over 400 parts per million (about 400 ppm) currently to just over 30 ppm over the next billion years. For the vast majority of plants that rely on photosynthesis, such carbon sources are extremely scarce. Even under the most optimistic estimates, it will be difficult for them to continue to grow normally after 1.84 billion years ago.
Whether they are "baked to death" by high temperatures or gradually withered in a "carbon famine", research suggests that plants and complex ecosystems on the earth are likely to come to an end before the deadline in the next 2 billion years. Earlier, as solar radiation continues to increase, the global ocean may significantly vaporize in about 1.5 billion years, and the only remaining water bodies will exist on the surface in the form of scattered "water pockets", which will further compress the living space for vegetation.
However, even if surface plants disappear completely due to environmental extremes, the end of life may not come immediately. Some previous theories and simulations have shown that microorganisms in deep underground environments may still persist for a longer period of time, delaying the "death breath" of the Earth's biosphere by another billion years. Such life forms may continue to evolve in extremely barren and high-temperature settings, relying on groundwater, rock chemical reactions, and weak energy sources.
The study author also pointed out that this series of deductions were conducted under the premise of "no external intervention", which means that humans or other potential intelligent life will not carry out large-scale engineering changes to the earth's environment in the future. In fact, the idea of extending the habitable period through "geoengineering" or "cosmic engineering" has long existed, such as changing the Earth's orbit, adjusting atmospheric composition, or laying out sunshade structures to buy extra survival time for the biosphere. On the contrary, human behavior such as excessive emission of greenhouse gases may also accelerate the decline of some ecosystems in the short term, adding more variables to the long-term fate.
The author emphasizes that the current photosynthetic system has been highly adapted to the existing environment in terms of carbon source utilization and heat tolerance, but future evolution may still bring new mechanisms beyond what is imagined today. For example, new photosynthesis pathways and extremely drought- and heat-tolerant plant structures may, to a certain extent, redefine the "finish line" of green life on earth. However, in the large-scale context dominated by solar evolution, atmospheric composition, and geological processes, any biological improvement is difficult to completely escape the constraints of physical and chemical boundaries.
From an astronomical point of view, the sun will evolve into a red giant in billions of years, and will eventually involve or burn the inner planets, including the Earth, to the point where they are uninhabitable. This is seen as the ultimate fate of the Earth. What the latest research depicts is a long and relatively clear "countdown" that life on the earth's surface, especially the plant world, may go through before this ultimate finale. On this time scale, human civilization is only a very short moment, but its impact on the future of the earth's ecology may far exceed its own existence.
From the perspective of scientists, such long-term predictions are not only an academic discussion of planetary evolution, but also provide us with a unique perspective on current environmental issues. When we are worried about climate change and ecological destruction in recent decades and centuries, the existence of a long-term "green finish line" reminds mankind that maintaining a world suitable for the reproduction of complex life itself is a precious and fragile opportunity. At some point in the distant future, when the last leaf wilts in a high temperature and carbon-poor environment, the Earth will bid farewell to its billion-year "green chapter," and this is exactly the scientific picture that current research is trying to paint.