When might life on the earth end?

Researchers from the U.S. have estimated how long photosynthetic life will last on the earth. As the sun ages, it also becomes brighter, eventually emitting a colour too hot for plants to survive.

Previous studies had tried to answer this question using simplified climate models, finding the biosphere’s twilight could occur in 100 million to 900 million years. The new study made use of a more sophisticated model, which also accounted for the effects of clouds, humidity, and planetary circulation on temperature. The new estimate: around 1.68 billion years for land plants and total extinction by 1.87 billion years.

The researchers explored two primary trajectories of future climate. The first, called strong weathering, assumed the planet’s carbon cycle could successfully draw carbon dioxide out of the atmosphere to offset the sun’s heat. While the traditional minimum for plant survival is 10 parts per million (ppm) of carbon dioxide, the authors suggested that crassulacean acid metabolism plants and certain aquatic species could even survive at as low as 1 ppm. This could extend the lifespan of the vegetative biosphere to around 1.84 billion years.

In the second trajectory, weak weathering, carbon dioxide levels remained constant while the temperature rose. In around 1.68 billion years, the global average surface temperature reaches the thermal limit for complex life. Around 1.87 billion years from now, the climate becomes too hot for all land plants, marking the end of the vegetative biosphere. And in 2.1 billion years, the earth begins losing its oceans to space.