Saturday, November 19, 2016

Stephen Hawking Again Warns Of "Deadline" For Humans To Leave Earth

Professor Hawking’s insights shaped modern cosmology and inspired global audiences in the millions.
Stephen Hawking: Says humans have 1,000 years to find another planet or the species will not survive.

Physicist Stephen Hawking, speaking on Tuesday at the Oxford University Union, again warned of multiple threats facing humans on their home world and emphasized the need to look for another abode, likely an exoplanet.  He estimated we had a maximum of 1,000 years to find another habitable world to colonize. Remaining on Earth any longer places humanity at great risk of extinction, possibly from a planet killer asteroid, e.g.

Hawking said:

"We must continue to go into space for the future of humanity. I don't think we'll survive another 1,000 years without escaping our fragile planet."

In respect of threats like the above, he said:

"Though the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time and becomes a near certainty in the next thousand or ten thousand years."

Which is clearly the case for Apollo asteroids as I pointed out in the preceding link. Hawking added:

"By that time we should have spread out into space, and to other stars, so a disaster on Earth would not mean the end of the human race."

I think he has a point, but would put the countdown clock until oblivion on Earth closer to 500 years. The reason? If we wait beyond then we will not have the resources to construct the ships needed to leave the planet. Also, it is likely by then that conditions associated with the runaway greenhouse will have fully set it, making it difficult if not impossible to get to safety. 

Already we are seeing havoc spread with the decimation of coral reefs around the world, the future potential for catastrophe having been reported in the journal PLOS by Linwood Pendleton, e.g.

Thus we've beheld once healthy coral reefs, e.g.
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turn into bleached and devastated reefs, e.g.

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endangering coastal communities because of the potential for higher sea level (62 million people live less than 33 feet above sea level), more damaging high tides, while also decimating economic life as millions will be deprived of their main sources of food, income - given the death of ocean species dependent on the coral reefs.

Much of this transformation is directly tied to increasing ocean acidification, itself tied to warmer oceans.  As noted in earlier posts: the seas absorb CO2 from the atmosphere, forming carbonic acid. The particular chemical reaction is:

H2O + CO2 -> H2 CO3

The lower the pH level of the seawater ('7' is neutral pH), the more acidic. This is also worrisome because mass extinctions of marine creatures in the past have been linked to instances of increased ocean acidification. Thus,  the current incremental change could also threaten important species. This according to Baerbel Hoenisch, the paleoceanographer at Columbia who was lead author of a  2012  paper that appeared in the journal Science. As he noted:

If industrial carbon emissions continue at the current pace, we may lose organisms we care about — coral reefs, oysters, salmon,”

As recently as 2012 scientists from Columbia University, which led the research. have found surging levels of carbon dioxide in the atmosphere that forced down the pH of the ocean by overall 0.1 mean unit in the last century. This is 10 times faster than the closest historical comparison from 56 million years ago. It's deadly serious because - like the margins for ushering in a runaway greenhouse effect, the margins of safety for acidic oceans are extremely low. Hence, one can't tell by the small magnitude of numerical pH that the increment change is nothing to fret over.

According to ocean research scientist Carles Pelejero, depending on how we humans respond - whether we take action or continue fouling our waters- the pH could reach a low of 7.7 by 2100.  (Note that while technically not in the "acid scale"  i.e. pH  less than 7, we are talking about the direction of the pH change, toward higher acidity.)

One of the most horrific findings by Peljero's team was associated with the PETM or Palo-Eocene Thermal Maximum, 55 million years ago. Over a 100ky period the evidence of samples showed a massive die off of shell -based life. If projections hold the same will occur by the end of this century.
An associated worry is that a stable, solid form of methane (clathrates) may be disrupted by current ocean chemical changes in what is called the "clathrate gun hypothesis". Should disruption occur, by changes in the ocean water chemistry and higher temperatures, it would mean the release of a greenhouse gas vastly more damaging than CO2.  In other words, we are looking at a "sixth mass extinction" even possibly within many current human infant's lifetimes.

Humans already drove to extinction many land-based, large animal species (in the Late Quaternary Extinction Event) and are now driving other large animals - mainly in the oceans - to extinction. See, e.g.

Hawking himself ranks the ravages of global warming right up with disasters like a Torino 9 asteroid hit, but I'd rank the former even more important because, first, it is almost certainly more immediate, and secondly, when the (more probable) runaway greenhouse sets in the life or death margins will be much narrower than they are today. In a previous post, in fact, I showed how perilously close in time we are to the cusp of the runaway..

The temperature of the planet is currently out of balance by 0.6W/ m2  and this is almost entirely due to the annual rate of CO2 concentrations increasing. Further,  every increase in CO2 concentration by 2 ppm increases the radiative heating effect by 2 W/ m2.  The late Carl Sagan who wrote the generalist essay "Ambush - The Warming of the World", estimated (in a CNN interview with Ted Turner in 1990) that the runaway would emerge when the mean global temperature exceeds 6 degrees Celsius. Right now, we are well on the way to reaching 4 C by 2100.  Prof. Gunter Weller estimated it would kick in when the CO2 concentration level of 600 ppm is surpassed. If it is at 400 ppm now - by many conservative measures -  then doing the math (adding 2 ppm  per year and increasing radiative heating effect by 2 W/ m. This gives us approximately 100 years - making Hawking's deadlines at least a factor 5 closer in time and hence,  more critical to meet.

As for Hawking's other cited major threat to human survival - A.I. -- or unchecked artificial intelligence-  while it is putatively a distant threat to our species I do not see it as an immediate threat like the runaway greenhouse effect.

As far as likely planets for humans to colonize in the short term, Mars appears obvious though it will need some terraforming (Google the term to learn more.) . Finding an exoplanet - given the closest (Proxima Centauri B in the triple star Alpha Centauri system)-  is 4.3 light years distant, is out of the question in the short term. It is simply a step too far unless humans suddenly discover near sub-light travel (e.g. 0.8c) and have the resources as well as governmental or commercial impetus to act in emergency mode - which I doubt.

See also:


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