Eventually, though, the warming sun will cause CO2 levels to fall so low that plants will start to die. First to go will be the C3 plants, so called because their photosynthesis process involves a molecule containing three carbon atoms. Most plants are of the C3 type, including wheat, rice, barley, oats, soybeans, peanuts, coconuts, bananas, potatoes, cotton, and most trees. In about 200 million years, when the CO2 concentration drops below 150 parts per million (it is at 400 today), C3 plants will disappear.
Civilization relies mostly on C3 plants, which make up about 85 percent of global agricultural production by dollar value. Another class of plants are C4 plants, which employ a form of photosynthesis that involves four carbon atoms and is more efficient under many conditions. Although C4 plants make up only about 3 percent of plant species, they account for about 25 percent of the total photosynthesis on Earth. In order to survive the die-off of C3 plants, we will probably turn to genetic engineering to expand the list of C4 plants. Today, C4 plants include corn, sorghum, millet, and sugarcane, as well as some grasses and weeds.
Efforts are already underway to convert rice from a C3 plant into a C4, which would result in about 50 percent larger harvests under present-day conditions. At 100 ppm CO2, the only rice on Earth would be C4 rice. C4 plants are thought to have evolved in response to the ongoing depletion of CO2. It is likely that as C3 plants die off, C4 species will continue to expand naturally to fill the newly opened niches in the ecosystem.
Unfortunately, about 300 million years after C3 plants disappear, C4 plants will die out too. When the CO2 concentration drops below 10 ppm, neither type of plant will remain.
Once plants disappear and cease replenishing atmospheric oxygen, animals will begin to die out. Currently, there are no known significant non-biological sources of oxygen on Earth. Once the plants are gone, oxygen will be a non-renewable resource. Large animals would probably asphyxiate within a few million years. Smaller and hardier creatures might last longer. Some types of microbes will probably survive by using metabolic reactions that do not rely on carbon dioxide or oxygen, but instead use materials such as sulfates or iron.
So that’s the number: In a paltry 500 million years or so, no humans will remain on the surface of the Earth—at least, not outside of some hypothetical controlled environment. And things get worse from there. After the atmospheric CO2 is gone and no longer able to regulate Earth’s surface temperature, things will start to get very hot. In about a billion years, the average surface temperature will increase to above 45 degrees Celsius from the current 17 degrees Celsius. Important biochemical processes turn off at temperatures above 45 degrees Celsius, leaving most of the planetary surface uninhabitable. Animal life will need to migrate to the cooler poles to survive; but by 1.5 billion years from now, even the poles will be too hot. Not even cockroaches will survive.
- How to Survive Doomsday
Civilization relies mostly on C3 plants, which make up about 85 percent of global agricultural production by dollar value. Another class of plants are C4 plants, which employ a form of photosynthesis that involves four carbon atoms and is more efficient under many conditions. Although C4 plants make up only about 3 percent of plant species, they account for about 25 percent of the total photosynthesis on Earth. In order to survive the die-off of C3 plants, we will probably turn to genetic engineering to expand the list of C4 plants. Today, C4 plants include corn, sorghum, millet, and sugarcane, as well as some grasses and weeds.
Efforts are already underway to convert rice from a C3 plant into a C4, which would result in about 50 percent larger harvests under present-day conditions. At 100 ppm CO2, the only rice on Earth would be C4 rice. C4 plants are thought to have evolved in response to the ongoing depletion of CO2. It is likely that as C3 plants die off, C4 species will continue to expand naturally to fill the newly opened niches in the ecosystem.
Unfortunately, about 300 million years after C3 plants disappear, C4 plants will die out too. When the CO2 concentration drops below 10 ppm, neither type of plant will remain.
Once plants disappear and cease replenishing atmospheric oxygen, animals will begin to die out. Currently, there are no known significant non-biological sources of oxygen on Earth. Once the plants are gone, oxygen will be a non-renewable resource. Large animals would probably asphyxiate within a few million years. Smaller and hardier creatures might last longer. Some types of microbes will probably survive by using metabolic reactions that do not rely on carbon dioxide or oxygen, but instead use materials such as sulfates or iron.
So that’s the number: In a paltry 500 million years or so, no humans will remain on the surface of the Earth—at least, not outside of some hypothetical controlled environment. And things get worse from there. After the atmospheric CO2 is gone and no longer able to regulate Earth’s surface temperature, things will start to get very hot. In about a billion years, the average surface temperature will increase to above 45 degrees Celsius from the current 17 degrees Celsius. Important biochemical processes turn off at temperatures above 45 degrees Celsius, leaving most of the planetary surface uninhabitable. Animal life will need to migrate to the cooler poles to survive; but by 1.5 billion years from now, even the poles will be too hot. Not even cockroaches will survive.
- How to Survive Doomsday
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