När blir jorden obeboelig?

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans.

The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to lethal levels for plants (10 ppm for C4 photosynthesis) in 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years. After another billion years all surface water will have disappeared and the mean global temperature will reach 70 °C. The Earth is expected to be effectively habitable for about another 500 million years, although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere. Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO2 due to reduced volcanism,and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.

As the global temperature of the Earth increases, it will increase the rate of weathering of silicate minerals. This in turn will decrease the level of carbon dioxide in the atmosphere. In 100 million years from the present, the concentration of CO2 will fall below the critical threshold needed to sustain C3 photosynthesis. However, C4 carbon fixation can continue at much lower concentrations, down to above 10 parts per million. Thus plants using C4 photosynthesis will be able to survive until about a billion years from now.