Scientists calculate when last plant on Earth will die; answer is farther than you think

Every plant alive today, from the tallest rainforest tree to the smallest patch of moss, will eventually disappear, but a new scientific study suggests that moment is much further away than most previous research believed. Researchers Jacob Haqq-Misra of the Blue Marble Space Institute of Science and Eric Wolf of the University of Colorado Boulder have calculated that Earth's vegetative biosphere could continue supporting plant life for roughly another 1.8 to 1.87 billion years, considerably longer than earlier estimates that put the number closer to 0.9 to 1.5 billion years. The extended timeline comes down to a more sophisticated understanding of exactly how a slowly brightening sun and a shrinking supply of atmospheric carbon dioxide will eventually make the planet uninhabitable for anything that photosynthesises. Why the sun is the real countdown clock for life on Earth The entire question of when plants will die out ultimately traces back to one simple, unavoidable fact about our star. Main sequence stars like the sun steadily grow brighter as they age, and this increasing brightness means Earth's overall energy balance keeps shifting over deep time, gradually pushing surface temperatures upward across hundreds of millions of years. According to the study published in the Journal of Geophysical Research: Atmospheres, researchers used a three dimensional climate model to calculate steady state conditions on Earth at various points across the next two billion years, accounting specifically for this rising solar output alongside changing atmospheric carbon dioxide levels. The two very different ways plants could eventually die out The study modelled two distinct future scenarios, each ending with the same ultimate outcome but arriving there through entirely different mechanisms. In what researchers call the strong weathering scenario, Earth's natural rock weathering process continues pulling carbon dioxide out of the atmosphere efficiently even as the sun brightens, keeping surface temperatures relatively stable but steadily starving plants of the carbon dioxide they need for photosynthesis, a decline the researchers calculate would kill off the vegetative biosphere around 1.84 billion years from now. In the alternative weak weathering scenario, carbon dioxide levels stay comparatively steady while temperatures instead climb relentlessly, eventually reaching around 65 degrees Celsius, hot enough that no land plant could survive, a threshold the model places at approximately 1.87 billion years into the future. Why the new estimate reaches further than earlier research Previous influential research on this exact question, including a widely cited study by Ken Caldeira and James Kasting published in the journal Nature, had estimated that a biosphere relying on C4 photosynthesis, the pathway used by grasses, corn and sugar cane, could survive for somewhere between 0.9 and 1.5 billion years. Haqq-Misra and Wolf's newer model extends this window considerably by revising two key assumptions used in earlier work, lowering the minimum carbon dioxide concentration needed to sustain photosynthesis and adjusting how strongly rock weathering actually depends on rising surface temperature. Their three dimensional climate model also directly addressed a known weakness in earlier one dimensional models, which the researchers found tended to overestimate how much warming would occur as solar output increased and carbon dioxide levels shifted. Why some plants might hold on even longer than the model suggests One particularly interesting detail buried within the study is its treatment of plants that use especially efficient methods of gathering carbon dioxide. CAM plants, a group that includes cacti, pineapples and agave, are unusually good at collecting carbon even when it grows scarce in the surrounding air, and some aquatic plants and algae have the added advantage of drawing on bicarbonate dissolved directly in water rather than relying purely on atmospheric gas. The researchers suggest these hardier photosynthetic strategies could allow small pockets of plant life to persist for a time even after conditions become lethal for more conventional land vegetation, extending the very tail end of the biosphere's survival slightly further still. An ending tied to the fate of Earth's oceans Perhaps the most striking conclusion to come out of the research is how closely the final disappearance of plant life lines up with another looming planetary milestone, the eventual loss of Earth's oceans. The researchers noted that this alignment suggests Earth's photosynthetic biosphere could remain viable in some form right up until the point where the planet begins losing its water altogether, meaning that once plant life truly reaches its end, it may do so almost in tandem with the oceans themselves rather than dying out considerably earlier, as some previous models had implied. A distant deadline, but a fixed one all the same None of this means Earth's plants face any imminent threat from these particular processes, since the timelines involved stretch nearly two billion years into the future, an almost unimaginable span compared to the roughly 300,000 years modern humans have existed. What the study does offer is a clearer, more carefully modelled picture of the very outer limit of life on this planet, tying the eventual end of photosynthesis to the same deep, slow astronomical and geological forces that will eventually reshape Earth in ways far more dramatic than anything currently facing the natural world. As Haqq-Misra himself put it in comments accompanying the study, life on Earth has proven remarkably adaptive throughout its long history, and this new estimate suggests that adaptability may carry plant life considerably further into the planet's future than scientists had previously dared to calculate.