Global warming: Tunguska impact?

[Dr Mordrid]

Abstract: http://arxiv.org/abs/physics/0510042

PDF: Tunguska.pdf

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Physics, abstract
physics/0510042

From: Vladimir Shaidurov
Date (v1): Thu, 6 Oct 2005 05:05:12 GMT (208kb)
Date (revised v2): Mon, 6 Mar 2006 13:16:12 GMT (424kb)

Atmospheric hypotheses' of Earth's global warming
Authors: V. Shaidurov
Comments: New Fig and minor corrections, format correction
Report-no: University of Leicester, Technical Report No. MA-05-15
Subj-class: Atmospheric and Oceanic Physics; Physics and Society

When analyzing the mean-year trend of the Earth's surface temperature for the past 140 years one can discern two sections of monotone linear increase of temperature during two last industrial centuries. The first one begins somewhere in the period 1906-1909. The previous segment demonstrates a weak decrease in the temperature trend, not increase. For explanation of this sudden break we look for a phenomenon of cosmic scale during this time which could have given rise to beginning of global warming with a significant probability. On the 30th June 1908 Tungus meteorite exploded with the power of ~15 Mt TNT at an altitude of ~10 km. Such an explosion could cause considerable stirring of the high layers of atmosphere and change its structure in mesosphere. The difference between this mesosphere catastrophe and atmospheric nuclear tests that cause another break in the temperature plot is discussed. The purpose of this report is to open the debate and to encourage discussion among scientists.

[ND66]

I hope that this will NOT be an excuse to blow up a couple of nukes here and there… .


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[Brian Ellis]

OK, I'm replying only to your abstract.

1. As the presumed meteoroid (not meteorite) - could have been something else - happened in 1908, I fail to see how that would affect temperature conditions 1906-1909.

2. The event took place at ~10 km altitude, which is tropopausal ie in the boundary between the troposphere and the stratosphere

3. The mesosphere is at altitudes of 50 - 85 km, nowhere near where it happened and there is little air in the stratosphere to permit a shock wave to be propagated to the mesosphere to cause "considerable stirring"

4. The energy in a 15 Mt event is negligible compared with the total energy received by the earth in a single day from solar radiation, albeit the nature of the event is different.

5. Let us imagine that a 15 Mt explosion occurred at the tropopause. What would happen? Firstly, there would be accelerated intermixing of tropo- and strato- spheric air and more natural, man-made and meteoroidal pollution would reach the stratosphere than normal. Most of the chemical pollution would be photolysed in a fairly short time, but the dust would not be, forming an aerosol. Within about 15 days this would be dispersed in a belt at the latitude of the event. Within a year, it would be uniform across the hemisphere, with little penetration into the other hemisphere (this would take about 10 years). Such a fine stratospheric aerosol would have an atmospheric residence time of about 30 days, so that 63% of the volume would fall to earth in 1 month, 86% in 2 months, 95% in 3 months and so on. The remaining dust could conceivably block some solar radiation, causing cooling, not warming. However, assuming it was a meteoroid (it may have been a comet which would produce little dust), it would be small as a celestial body, probably just a few hundred metres across, so the volume of dust would not be enormous when spread, even at the same latitude. I cannot envision much change in weather, except possibly in supplying nuclei for seeding clouds for a short time.

6. An explosion of this magnitude would probably have some electromagnetic radiative effects, but these would be limited to a small area, essentially line of sight. I could not speculate on the spectrum without knowing the cause but I would imagine that it would probably be mainly heat, light, maybe up to X-rays. This could acerbated by very high potential differences between the fireball and the earth, causing massive lightning strikes.

7. Let's compare 15 MT with some known phenomena.

* The 1980 eruption of Mount St. Helens was reportedly equivalent to 27,000 Hiroshima-sized atomic bombs - which translates roughly to 350 megatons.
* The 1912 eruption of Novarupta in Alaska was ten times the size of Mount St. Helens. That is about 3500 megatons.
* The 1883 eruption of Krakatoa was about 50% larger than Novarupta. That is about 5250 megatons.
* The 1815 eruption of Mount Tambora was about seven times larger than Novarupta. That is about 24500 megatons.
* The 1650 BC eruption of Santorini was much larger than Mount Tambora.

(http://www.biocrawler.com/encyclopedia/Megaton)

Taking Krakatoa as an example, we know that about 25 km3 of rock disappeared from the face of the earth. This volume is enormous compared with the possible meteoroid. It is believed that ~ 19 km3 fell within days over a radius of a few 100 km, so about 6 km3 were unaccounted for and could be the majority projected upwards into the stratosphere. There is little doubt that this caused a drop of temperature of ~1.5°C, globally averaged, over the following year. It took 5 years before the remaining dust was largely dissipated. AFAIK, there was no significant similar effect after the Tunguska event. But Krakatoa was 350 times more powerful, so this is not surprising.

My conclusion:
The theory does not hold water and the lack of correct terminology betrays the fact that the author is not a scientist.