Earth’s future and the future of life 11 November 2016

Earth’s Future During the next four billion years, the luminosity of the Sun will steadily increase In about one billion years, the solar luminosity will be 10% higher than at present Resulting in a runaway evaporation of the oceans As a likely consequence, plate tectonics will come to an end, and with them the entire carbon cycle. In about 2−3 billion years, the planet's magnetic dynamo may cease, causing the magnetosphere to decay and leading to an accelerated loss

Earth Now

Human influence Humans play a key role in the biosphere, with the large human population dominating many of Earth's ecosystems. This has resulted in a widespread, ongoing mass extinction of other species during the present geological epoch, now known as the Holocene extinction. More than a third of the land surface has been modified by human actions, and humans use about 20% of global primary production. The concentration of carbon dioxide in the atmosphere has increased by close to 30% since the start of the Industrial Revolution

Greenhouse Effect The net result would be a loss of the world's sea water in about 1.1 billion years With no water to lubricate them, plate tectonics would very likely stop By 2.8 billion years from now, the surface temperature of the Earth will have reached 422 K (149 °C; 300 °F), even at the poles. At this point, any remaining life will be extinguished due to the extreme conditions

The World in 2050 The world will be warmer than today in 2050 CO2 concentration levels will reach twice the pre-industrial level Life will persist, although coastal cities may be drowned

Could we trigger a runaway greenhouse effect by adding carbon dioxide to the atmosphere? Hansen: “If we burn all reserves of oil, gas, and coal, there’s a substantial chance that we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.” Goldblatt and Watson: “The good news is that almost all lines of evidence lead us to believe that it is unlikely to be possible, even in principle, to trigger full a runaway greenhouse by addition of noncondensible greenhouse gases such as carbon dioxide to the atmosphere.”

What to survive: Random events Impacts from comets can trigger a mass extinction of life on Earth. These disruptive encounters occur at an average of once every 45 million years Continental drift: Plate tectonics continues until the Earth’s surface is as hot as Venus

Future of Continental Drift

Solar Evolution The result of helium production from hydrogen fusion has been a steady increase in the energy output of the Sun. When the Sun first became a main sequence star, it radiated only 70% of the current luminosity. The luminosity has increased in a nearly linear fashion to the present, rising by 1% every 110 million years The hydrogen fuel at the core will finally be exhausted in five billion years: The Sun will become a Red Giant

The Sun as a Red Giant The most probable fate of the planet is absorption by the Sun in about 7.5 billion years, after the star has entered the red giant phase and expanded to cross the planet's current orbit.

Sun as Red Giant

Red giant stage The Sun will expand as it gets hotter The most rapid part of the Sun's expansion into a red giant will occur during the final stages, when the Sun will be about 12 billion years old. It is likely to expand to swallow both Mercury and Venus, reaching a maximum radius of 1.2 AU (180,000,000 km).

The likely story What will happen to the Earth? We tend to worry about issues like climate change that can have an impact over periods of time comparable to an average human lifetime. For the Earth, however, the biggest changes generally happen over hundreds of millions or billions of years. Supercontinents come and go, mass extinctions wipe out almost all life, and changes in the surrounding Solar System have an impact. It is ultimately the Sun that will decide Earth's fate. Billions of years from now, as our aging star begins to runs out of hydrogen fuel, it will change into a red giant and expand out into the inner Solar System as far out as the Earth's orbit.

Summary The Sun is getting brighter: Venus already suffered a runaway greenhouse effect, and the Earth will, too Mars may become more habitable, or easier to terraform Human production of greenhouse gasses will warm the Earth, oceans will rise, glaciers and poles will melt, but likely no runaway Life on other planets will have similar problems: Remember the CHZ (it may not exist) Eventually the Sun expands, and swallows the Earth, but billions of years from now ESP’s may have had past life, or future: Study Venus and Mars to find signs