Heavy Weather

I’ve been a bit out of touch, as readers will understand, and have just noticed two recent items in the scientific news. Both have to do with the climatic effects of largish objects colliding with the Earth.

The first item has to do with the cause of global warming generally, and in particular the rise in average temperature over the last hundred years.

According to Vladimir Shaidurov of the Russian Academy of Sciences, the apparent rise in average global temperature recorded by scientists over the last hundred years or so could be due to atmospheric changes that are not connected to human emissions of carbon dioxide from the burning of natural gas and oil. Shaidurov explained how changes in the amount of ice crystals at high altitude could damage the layer of thin, high altitude clouds found in the mesosphere that reduce the amount of warming solar radiation reaching the earth’s surface.

Shaidurov believes he has found a likely culprit for the 20th-century rise in the Earth’s temperature – the extraordinary Tunguska Event of 1908, which has in turn been chalked up to everything from comets to black holes to methane gas to UFOs.

The second story is about the impact that supposedly led to the Cretacious-Tertiary (abbreviated K-T, for some reason) extinctions that marked the end of the reign of the great reptiles. The idea that a meteoric impact was responsible for these extinctions was put forward in 1980 by physicist and Nobel laureate Luis Alvarez, along with his son Walter, a geologist, based on their observation of a widespread layer of iridium in rock strata near the K-T boundary. In 1990, geologists Alan Hildebrand and Glen Penfield identified an enormous impact crater, of the right approximate age, at the northern tip of the Yucatan Peninsula, centered on a spot called Chicxulub. It is estimated that the force of the explosion was in the order of 190,000 gigatons of TNT ( the largest explosive device ever detonated by man having been a paltry 20 megatons).

But a Dutch scientist, Markus Harting, has found evidence, in the form of weathered glass spherules in layers of rock lying below the iridium layer, that the Chicxulub event looks to have happened 300,000 years too early to account for the dinosaur’s demise. Harting suggests that the real culprit was a second, later impact.

Do forgive me if you ‘ve already heard about all of this; I thought it worth mentioning for those who hadn’t, and I find that I still haven’t quite regained the focus needed to write about some of the other things I’ve been mulling over.

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2 Comments

  1. Nick N. says

    The best explanation I have heard for the Tunguska event is the explosion of a large chunk of ice entering the atmosphere. This is consistent with the increase in atmospheric moisture that Shaidurov (If I recall correctly) propose as the mechanism involved.
    Another point that has been brought up (attributed to Professor Obvious) is that global temperatures are affected by variations in solar output, see:
    http://solar-center.stanford.edu/sun-on-earth/varsun.html

    Posted April 4, 2006 at 10:52 am | Permalink
  2. Malcolm says

    Hi Nick,

    Yes, I’d heard about the solar-variation idea also. I’m surprised nobody’s tried to pin it on the Bush administration yet…

    Posted April 4, 2006 at 11:42 pm | Permalink