Many cultures have stories of the End of Times, when the current world comes to an end (and sometimes a better one is born from the ruins): Revelations, Ragnarok, etc.
Even today, we can reasonably for see the "End of the World As We Know It":
- That is, sufficient change in the global circumstance that the quality and style of our lives would be radically transformed
- Not necessarily the same thing as the total destruction of Life or the whole Earth (although those would certainly count!!)
- Some "End of the World" scenarios have human influence
- But some are "perfectly natural"...
Here are a list of some examples of catastrophes without human cause:
Bolide Impact:
Bolide = comet or asteroid which impacts with Earth's atmosphere or surface. As they burn-up/impact, they release tremendous amounts of energy into the environment.
And if they strike the surface, they vaporize large quantities of matter and fling it into the atmosphere.
|
Famous historic bolide impact: Tunguska Event. On June 30, 1908, a bolide (likely a ~60 m diameter asteroid) impacted at or above central Siberia, releasing the equivalent of 10-15 million tons of TNT (i.e., a 10-15 Mt explosion). As it was, it devastated only wilderness (see the photo of flattened forests, photographed by Soviet expeditions to that area in 1927). However, had it occurred over a major metropolitan region, it would have destroyed that city. And had such an event happened during the Cold War, it would almost certainly be interpreted as a thermonuclear explosion. |
|
Supervolcanoes:
We have previously explored the effects of extremely large historic volcanoes like Pinatubo and
Tambora: decreased insolation due to dust and sulfate aerosols; ash interference with aviation; etc.
|
However, there are much MUCH larger eruptions in even the geologically recent past which are orders of magnitude larger than even Tambora. These have been given the nickname "supervolcanoes" by BBC documentarians, and this name is catching on. To the right you see the extent of the ashfall of a single eruption of the Yellowstone Caldera from 600,000 years ago. This is by no means the only eruption of this scale from that one supervolcano: in fact, some were even larger! As you know, the eruption of one vastly smaller volcano in Iceland in the Spring of 2010 brought air travel over the North Atlantic to a stand still for about a week. An eruption on this scale might halt all air travel in the world for months! Additionally, it would cripple all forms of commerce in North America, and essentially stop American and Canadian agriculture for that season. Given that North American agriculture is one of the main food sources for most of the planetary population, a single eruption on this scale would produce unprecendented levels of famine and death around the world: population crashes far more severe than any combination of wars or plagues the world has ever seen. (And, of course, there is no reason whatsoever to think that the Yellowstone Caldera has stopped; indeed, it is still active and will eventually erupt again.) |
|
However, the above events--big as they are--are relatively short term event. Earth history has witnessed global events (bolides, volcanism, ocean processes, ice ages, etc.) that have had much longer term environmental effects.
We have previously mentioned the Paleocene-Eocene thermal maximum (PETM), an event 55.8 Ma in which for a geologically-short period of time (<10,000 years) the level of CO2 jumped to 3-4x the previous background level. (This jump is comparable to the upper end of anthropogenic greenhouse gas models, but from a higher starting point.) PETM saw a temperature increase of +4-5K at the tropics, +6-8K at the poles, and even +4-5 K in the deep sea.
Some consequences of this event:
- Extinction of many species of plankton, and of additional sea and land organisms
- A jump of ~3x background level of the amount of insect damage seen on leaves, lasting for about 10 kyr
- Short term (~a few ky) dwarfing of terrestrial animals, probably as a result of environmental stress
- Major changes in the habitat ranges of species: in particular, warming polar regions allowed the spread of subtropical and tropical animals from continent to continent over corridors which were once too cold for them to enter
The likely cause of PETM was due to a massive release of methane clathrates from the sea floor. (This matches the isotopic signature of the carbon increase.) In turn, this is likely due to a sudden burst of submarine volcanism in the northeastern Atlantic, as part of the tectonic rifting of Greenland from nothern Europe.
But bad as PETM was, it is still nothing like the REALLY bad stuff that can happen!! These are marked as mass extinctions: the sudden loss of a large fraction of Earth's species, which are not immediately replaced ecologically. The various mass extinctions have various causes, but in general the occur because some environmental factor changes at a rate and/or severity much greater than that for which evolution can compensate. (In other words, a species can only survive a mass extinction; it cannot adapt to it.) Two of the great mass extinction events have as their origins scaled-up versions of the types of disasters already mentioned:
- The Cretaceous-Paleogene Extinction (65.5 Ma): sometimes called the "Cretaceous/Tertiary" or simply
"K/T" extinction, using the old stratigraphic nomenclature. This is the most famous, the most recent, but not the
most intense of mass extinctions. This is the end of the "Age of Reptiles" and the dawn of the "Age of
Mammals", representing a major overhaul of both terrestrial and marine ecosystems.
- The major cause is the impact of a ~10-15 km diameter asteroid into what is now the Yucatan Peninsula of
Mexico. This blasted out a 180 km diameter crater (named Chicxulub after a local town), and represented a
1.8 x 10
8 Mt blast: equivalent to 1000-10,0000x the total nuclear arsenal at the height of the Cold War, or a century's worth of geothermal energy, all released at one spot in an instant - The impact blasted vast quantitites of material high into the atmosphere, some of which rained down
right away and others of which remained suspended stratospherically for a long time
- The material that fell down right way burned up for the most part in the atmosphere, producing a thermal pulse of ~8-10x the noon infrared flux at the equator. This lasted for minutes to hours, baking exposed flesh and leaf (although water and soil acted as a shield)
- The material that remained as suspended soot would have blocked insolation for weeks, possibly months, shutting down primary productivity
- And to make matters worse, the impact site was covered with carbonate rock, which burned with the heat of impact into (you guessed it) CO2, resulting in a post-impact greenhouse summer lasting for centuries
- The major cause is the impact of a ~10-15 km diameter asteroid into what is now the Yucatan Peninsula of
Mexico. This blasted out a 180 km diameter crater (named Chicxulub after a local town), and represented a
1.8 x 10
- The Permo-Triassic Extinction (251 Ma): the greatest of all mass extinctions, resulting in
perhaps 95% loss of marine species (or alternatively, only 5% survival at the species level, and thus much much much
lower survival rate at the individual level.) Again, it totally reorganized terrestrial and marine ecosystems.
- The cause here seems to have been the most super of supervolcanoes: the Siberian Traps. These are
a huge lava field in (not surprisingly) Siberia, covering an area of 5 x 10
6 km2 and representing a volume of about 3 x 106 km3 ! (If you were to spread such a volume evenly over North America, we would all be buried 121 m (~400') deep!) These eruptions occured over only 1 Myr or less. - This massive eruption released 12,000-18,000 Gt C into the atmosphere. In comparison, the current atmosphere
contains only 800 Gt C and preindustrial levels was only ~600 Gt C. While these giant levels were erupted in
pulses over the course of the eruptions and not as a single burst, they would accumulate in the atmospehere
much faster than they could be scrubbed out (i.e., the same problem we have in the Anthropocene, only several
orders of magnitude worse!)
- What is even more severe is that the warming of the oceans from carbon dioxide greenhouse effects reached the sea floor to such a degree that it caused massive degassing of oceanic clathrates, which themselves added to the global greenhouse
- This resulted not only in tremendous heat stresses, but in major changes in atmospheric and oceanic chemistry. On both land and sea, oxygen levels crashed (e.g., sea level conditions were as oxygen starved as what was previously typical of 4 km high mountains). The oceans also suffered extreme acidification and hypercapnia (too much carbon dioxide, a major biological stress on animals without sophisticated gills.)
- The cause here seems to have been the most super of supervolcanoes: the Siberian Traps. These are
a huge lava field in (not surprisingly) Siberia, covering an area of 5 x 10
When discussing these (and other) phenomena, it is important to distinguish between proximate and ultimate causes. Proximate causes are the events that directly bring about some change. Ultimate causes are the phenomena which spark the proximate cause. For example, the proximate cause of the sinking of the Titanic was the iceberg ripping a hole in its side; the ultimate causes included (among other things) inadequate design to deal with such a hole and the failure to spot the iceberg early enough in advance to turn the ship. In most cases, the proximate causes of damage in abrupt climate change is not the change itself.
For example, very few (if any) people will actually die of hypercapnia from increased carbon dioxide levels, or drown as sea level rises (it won't be THAT abrupt!). Instead, the climate catastrophes will include such proximate causes as: the collapse of food and water security, leading to famines; collapse of energy security and disruptions of transportation and industry; spread of environmental refugees, overwhelming local resources and spreading famine and disease; and all these leading to international instability and war.
Breaking news! In May, 2010 a new
study suggested that at the extreme end of predicted climate change, there actually will be
proximate causes of devastation more closely linked to the change itself. S.C. Sherwood and M. Huber
examined the physiological limits of individual human survival in the context of "wet-bulb" temperatures"
(Tw), the combination of ambient temperature and humidity. It was recongized that
exposure to Tw of >35
These are some of the problems we want to avoid, if at all possible. But how do we make it possible? We
face many major obstacles, both technological and social. We will explore these in much greater detail next semester,
but to whet your appetite, here is an example:
This is cartoon graph of the problems in dealing with climate science in the media. Most informed research
climatologists recognize the profound, potentially catastrophic effects of abrupt climate change, but they
are marginalized by the media as being "too extreme to report". Instead, the popular press considers
the (in fact highly conservative in terms of their predictions!) IPCC as being extreme, and the climate
change denial community as being informed. We'll talk more about how this happens in the Fall.
However, the popular press idea that this is just a "right-wing/left-wing", "business/environmentalism" conflict is dead wrong!! Even ignoring the extraordinarily important fact that reality and the Earth systems don't care one jot about human politics (!!), examine the following quotes and then their sources:
- "With inadequate preparation, the result [of abrupt climate change] could be a significant drop in the human carrying capacity of the Earth's environment."
- "The consequences of even relatively low-end global climate change include the loosening and disruption of societal networks. At higher ranges of the spectrum, chaos awaits."
- "Each year we delay action to control emissions increases the risk of unavoidable consequences that could necessitate even steeper reductions in the future, at potentially greater economic cost and social disruption."
No, these are not from publications by Al Gore, the Sierra Club, or other "left-wing" or "environmentalism" groups. They are, respectively, from An Abrupt Climate Change Scenario & Its Implications for United States National Security: Imagining the Unthinkable, a 2003 report by the Global Buisness Network for the Pentagon; The Age of Consequences: The Foreign Policy and National Security Implications of Global Climate Change (a 2007 joint report of the Center for Strategic and International Studies and the Center for a New American Security); and A Call to Action, a 2007 report by the U.S. Climate Action Partnership, a coalition of environmental groups and corporations from a number of industries including Chrysler, Dow, DuPont, Ford, General Electric, General Motors, Johnson & Johnson, PepsiCo, Shell, and Weyerhaeuser. So there are very much establishment, industrial, "right-wing" institutions who take the reality of climate change quite seriously.
And there is some positive news about carbon dioxide emissions in the U.S. A U.S. Energy Information Administration report in May 2010 showed that U.S. energy-related carbon emissions (although not transportation-related) had their greatest decline so far, and that while some of this was due to the economic downturn, much is due to a shift to non-carbon emitting energy generation. We will look into these in much greater detail next semester.
So it can be that as we shift to new methods of energy generation and transportation, we may overturn our previous ways of doing things, but for the better. The "End of the World as We Know It" does not have to be a bad thing!
