The Future of The Earth

Wednesday, April 8, 2015
12:07 pm

Edvard Munch's The Scream

As the picture above insinuates, the future is not good.

Now, when I'm talking about the future, I'm not talking about 100 years from now (although that's pretty bad too). I'm not even talking about 1,000 years from now. No, I'm talking in the realm of 7,000,000,000 (seven billion) years from now. When stars age, they gradually become bigger and brighter before finally becoming "red giants" where although they have the same mass, their volume is significantly larger. In seven billion years, the Sun may actually expand to a point where it engulfs the Earth. The Earth is currently 93 million miles, or 1 astronomical unit (AU), away from the sun (give or take 1.5 million miles depending on the season, as the Earth has an elliptical orbit and is further away from the sun during the Northern Hemisphere summer than the Northern Hemisphere winter). The diagram below has the sun with a diameter of 2 AU, meaning it has a radius of 1 AU and just barely engulfs the sun. Seeing as the sun is only 0.01 AU right now, this diagram shows that the sun as a red giant will be approximately 200 times wider, and using the formula for volume:

V

=

4

3

π

r

3

Where r = radius and pi (the Greek letter) is the ratio of a circle's circumference to its diameter (approximately 3.14), the volume of the sun as a red giant is predicted to be approximately 8 trillion times greater than the sun's current volume. They don't call it a giant for nothing. And the red color comes from the surface gradually cooling as it increases in volume.

Sun as a red giant compared to its current state. Credit: Oona Räisänen

But I'm getting ahead of myself here. Obviously, the Earth is kinda screwed if it becomes part of the sun. But we've got a number of hazards to watch out for before then.

Throughout the Quaternary Period (2.58 million years ago to the present), ice ages have been controlled by Milankovitch Cycles, which are changes in the Earth's orbit (eccentricity), axial tilt (obliquity), and amount of "wobbling" that the Earth's axis undergoes, kind of like a spinning top (precession). The exception, of course, is global warming due to increased greenhouse gases since the Industrial Revolution. However, regardless of any effects of from current anthropogenic global warming and greenhouse gas emissions, the Earth will likely enter its next ice age in 50,000 years (Berger and Loutre, 2002). If humans are still around by then and we haven't solved the carbon dioxide problem, an ice age may not occur. Additionally, we would be able to avoid an ice age altogether if we pumped enough carbon dioxide into the atmosphere to create an increased greenhouse effect to offset the decrease in solar radiation.

By 500,000 years, the Earth will likely have been hit by an asteroid 1km in diameter, assuming humans aren't still around and can't explode it in space or find a way to avoid it completely by delaying its impact (thermonuclear weapons are good for something!) (Hall and Ross, 1997), (Bostrom, 2002). By 1 million years, the Earth will have likely experienced a volcanic eruption similar in magnitude to the eruption of the Toba supervolcano 75,000 years ago, which was, as the picture below shows, much, much larger than the famed Mt. St. Helens eruption of 1980.

Photo Credit: USGS

Of course, now all that remains of Toba is a beautiful lake. However, it still has a magma system under the lake, so while it is a dormant volcano that is not erupting, it has the potential to erupt again, and thus is not extinct (Oregon State University). You wouldn't know it by looking from the tranquil picture of the crater lake below, but when Toba does erupt again, the results will be catastrophic, and the Earth will be plunged into a volcanic winter for approximately a decade with a period of cooler temperatures lasting for up to 1,000 years

Lake Toba. Photo Taken by A.M. & K.D. Hollitzer in 1996. Retrieved from Oregon State University Volcano World

NASA Landsat satellite image of Lake Toba. Credit: NASA

I've come across a lot of scary stuff in the Earth and space sciences, but the part I'm going to describe to you next may just be the scariest of all. And it's because it's our fault.

In 2 million years, coral reef ecosystems are expected to have finally completely recovered from ocean acidification. When I heard this, I was astounded. Two million years? That's an unfathomably long time from now. We're putting carbon dioxide into our atmosphere at an unprecedented rate, and we know that it is going to have drastic effects on sea life. Just look at the picture below! A note of caution... scientists aren't completely certain about how quickly global warming and ocean acidification will destroy coral reefs, so take the photograph with a grain of salt. Alarmists like to show this stuff for shock value. But the bottom line is that increased carbon dioxide will lead to increased ocean acidity and temperature, and this will decimate coral reefs around the world

The Effects of Ocean Acidification and Temperature Rise on Coral Reefs. Retrieved from Furman University's Ocean Acidification Page

The graph below is from the Intergovernmental Panel on Climate Change's (IPCC's) 5th Assessment report, and shows different carbon dioxide concentration scenarios. If we continue releasing CO2 at the rate we are currently doing so, we will reach 500 ppm in a couple decades. Just think... a couple centuries so start the dissolution of coral reefs, and 2 million years to rebuild them. I promise to have more blog posts on ocean acidification in the future, as I believe it is a subject that does not get as much attention as it should, mainly in the media but also in our educational institutions. In fact, ocean acidification was hardly discussed in any of my atmospheric science classes at the University of Washington, including those on climate.

CO2 Emission Scenarios from the IPCC 5th Assessment Report. Retrieved from Wasatch Weather Weenies Blog

A variety of interesting geological things will happen shortly after (in geological time). 10 million years from now, the East African Rift valley will finally spread open far enough to form a new ocean, (Haddock, 2008), and 50 million years from now, California will have slid up to Alaska and been subducted into the Aleutian Trench (Garrison, 2009). By 100 million years, we will have likely been hit by one of those huge asteroids like the one that killed the dinosaurs (Nelson, 2014). By 250 million years, the continents will likely have drifted together to form another supercontinent analogous to "Pangea," the supercontinent that existed 200-300 million years ago. However, this supercontinent will have likely broken up 450 million years from now (Williams and Nield, 2007).

But things really start to get interesting 600 million years from now. And by interesting, I mean depressing.

Dead Plants in Pots. Retrieved from Wikipedia.

As I stated before, stars gradually become brighter as they age. 600 million years from now, the sun is expected to become bright enough that there will be enough heat the atmosphere to evaporate a significant amount of water vapor and thereby cause heavy rain throughout the Earth. As this heavy rain falls, it combines with carbon dioxide in the atmosphere to make carbonic acid. This acid erodes the landscape through a process known as weathering. Eventually, this process, is expected to take the carbon dioxide levels in the atmosphere to a point below the vast majority of photosynthesizing organisms will die (Heath and Doyle, 2009). Normally, carbon dioxide would be continuously added to the atmosphere via volcanism, but so much water will have evaporated from the Earth's surface that rocks will become so hard that plate tectonics, the primary drivers for volcanism, will cease (O'Malley-James et al., 2012).

This process will continue, and by the next 200 million years, all photosynthetic life will be gone and multicellular life will die (Heath and Doyle, 2009).

One billion years from now, the sun will have become 10% more luminous. This doesn't sound like that much, but the average temperature of the Earth will now have risen to 116 degrees Fahrenheit (it's 61 degrees right now). And that's with next to no CO2 in the atmosphere! Why so hot? Well, this increase in solar radiation will also spur a "runaway greenhouse" where the oceans evaporate entirely (Schröder and Smith, 2008). Water vapor is the most important greenhouse gas in the atmosphere, and no single-celled organisms will be doubting that one billion years from now. In fact, eukaryotic life is expected to become extinct 1.3 billion years from now, with only prokaryotic life remaining (Franck et al., 2005). Prokaryotic life can be thought of "the most basic life there is."

And the news just keeps getting worse. By 2.3 billion years from now, the Earths outer core is predicted to freeze (Waszek et al., 2011). The outer core is currently liquid, and is responsible for creating the Earth's magnetic field. Without a magnetic field, our atmosphere would be blown away. By 2.8 billion years, our average surface temperature has risen to 296 Fahrenheit, enough to wipe out all life (O'Malley-James et al., 2012). By 3.5 billion years, Earth will be as hot as Venus (Hecht, 1994).

Five billion years from now, the sun will evolve into a red giant (Schroeder and Smith, 2008), and as previously stated, after 7 billion years, it will likely grow large enough to swallow the Earth. And that will be the end of our (not so blue) planet.

What the Earth might look like when the sun is a Red Giant. Retrieved from Wikipedia.

So what can humans do to stop this madness from happening?

Well, first of all, I believe we'll likely be extinct in the near future. Thermonuclear war is a very real possibility, and as crazy as it may sound, we have to be very careful or artificial intelligence may be able to develop some sort of sentience and destroy us. If we were alive 600 million years from now and wanted our dear plants to still be alive, we'd preferably see if we could move our orbit further away from the sun. But if we aren't around, this process is inevitable.

You think that's depressing? I don't think you want to know about the proposed "heat death" of the universe. I'll write about that soon.

References:

Berger, A & Loutre, MF (2002). "Climate: an exceptionally long interglacial ahead?". Science 297(5585): 1287–8. doi:10.1126/science.1076120.PMID 12193773.

Bostrom, Nick (March 2002). "Existential Risks: Analyzing Human Extinction Scenarios and Related Hazards". Journal of Evolution and Technology 9 (1). Retrieved 10 September 2012.

C. D. Hall and I. M. Ross, "Dynamics and Control Problems in the Deflection of Near-Earth Objects,"Advances in the Astronautical Sciences, Astrodynamics 1997, Vol.97, Part I, 1997, pp.613–631.

 Franck, S.; Bounama, C.; Von Bloh, W. (November 2005). "Causes and timing of future biosphere extinction". Biogeosciences Discussions 2 (6): 1665–1679.Bibcode:2005BGD.....2.1665F. doi:10.5194/bgd-2-1665-2005. Retrieved 19 October2011.

Garrison, Tom (2009). Essentials of Oceanography (5 ed.). Brooks/Cole. p. 62.

Haddok, Eitan (29 September 2008). "Birth of an Ocean: The Evolution of Ethiopia's Afar Depression". Scientific American. Retrieved 27 December 2010.

Heath, Martin J.; Doyle, Laurance R. (2009). "Circumstellar Habitable Zones to Ecodynamic Domains: A Preliminary Review and Suggested Future Directions".arXiv:0912.2482.

Hecht, Jeff (2 April 1994). "Science: Fiery Future for Planet Earth". New Scientist (subscription required) (1919). p. 14.

Lunine, J. I. (2009), "Titan as an analog of Earth’s past and future", European Physical Journal Conferences 1: 267–274, doi:10.1140/epjconf/e2009-00926-7.

Nelson, Stephen A. "Meteorites, Impacts, and Mass Extinction". Tulane University.

O'Malley-James, Jack T.; Greaves, Jane S.; Raven, John A.; Cockell, Charles S. (2012)."Swansong Biospheres: Refuges for life and novel microbial biospheres on terrestrial planets near the end of their habitable lifetimes". arxiv.org. Retrieved 2012-11-01.

Schroder, K. P.; Connon Smith, Robert (2008). "Distant Future of the Sun and Earth Revisited". Monthly Notices of the Royal Astronomical Society 386 (1): 155–163.arXiv:0801.4031. Bibcode:2008MNRAS.386..155S. doi:10.1111/j.1365-2966.2008.13022.x.

"Toba, Sumatra, Indonesia". Oregon State University.]

Waszek, Lauren; Irving, Jessica; Deuss, Arwen (20 February 2011). "Reconciling the Hemispherical Structure of Earth's Inner Core With its Super-Rotation". Nature Geoscience 4(4): 264–267. Bibcode:2011NatGe...4..264W. doi:10.1038/ngeo1083.

"When humans faced extinction". BBC. 2003-06-09.

Williams, Caroline; Nield, Ted (20 October 2007). "Pangaea, the comeback". New Scientist.