Another good post on Science Blog, which I just stumbled across today: A report on a controversial new theory to account for global warming.
On June 30, 1908, there was a cataclysmic event in Siberia that is still not completely understood. According to one eyewitness, a Shanyagir tribesman:
We had a hut by the river with my brother Chekaren. We were sleeping. Suddenly we both woke up at the same time. Somebody shoved us. We heard whistling and felt strong wind. Chekaren said, “can you hear all those birds flying overhead?” We were both in the hut, couldn’t see what was going on outside. Suddenly, I got shoved again, this time so hard I fell into the fire. I got scared. Chekaren got scared too. We started crying out for father, mother, brother, but no one answered. There was noise beyond the hut, we could hear trees falling down. Me and Chekaren got out of our sleeping bags and wanted to run out, but then the thunder struck. This was the first thunder. The Earth began to move and rock, wind hit our hut and knocked it over. My body was pushed down by sticks, but my head was in the clear. Then I saw a wonder: trees were falling, the branches were on fire, it became mighty bright, how can I say this, as if there was a second sun, my eyes were hurting, I even closed them. It was like what the Russians call lightning. And immediately there was a loud thunderclap. This was the second thunder. The morning was sunny, there were no clouds, our Sun was shining brightly as usual, and suddenly there came a second one!
Me and Chekaren had some difficulty getting under from the remains of our hut. Then we saw that above, but in a different place, there was another flash, and loud thunder came. This was the third thunder strike. Wind came again, knocked us off our feet, struck against the fallen trees.
We looked at the fallen trees, watched the tree tops get snapped off, watched the fires. Suddenly Chekaren yelled “Look up” and pointed with his hand. I looked there and saw another flash, and it made another thunder. But the noise was less than before. This was the fourth strike, like normal thunder.
Now I remember well there was also one more thunder strike, but it was small, and somewhere far away, where the Sun goes to sleep.
This was the “Tunguska event.” The scientific near-consensus is that it was caused by the airburst from a meteorite, comet or asteroid hurtling toward Earth, exploding 6-10 kilometers above the surface. It destroyed, among other things, 60 million trees. But it left no crater, which indicates the object exploded into flaming dust before impact, releasing 10-15 megatons of energy into the air. The skies above Europe glowed at night for several evenings afterward — bright enough to read by.
Vladimir Shaidurov from the Russian Academy of Science now believes this cosmic event might be responsible for the pronounced climate change that began early in the 20th Century– global warming. According to Shaidurov’s theory, “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.” This effect could be the result of the Tunguska event. From Science Blog’s post:
(T)he most potent greenhouse gas is water, explains Shaidurov and it is this compound on which his study focuses. According to Shaidurov, only small changes in the atmospheric levels of water, in the form of vapour and ice crystals can contribute to significant changes to the temperature of the earth’s surface, which far outweighs the effects of carbon dioxide and other gases released by human activities. Just a rise of 1% of water vapour could raise the global average temperature of Earth’s surface more then 4 degrees Celsius.
Water vapour levels are even less within our control than CO2 levels. According to Andrew E. Dessler of the Texas A & M University writing in ‘The Science and Politics of Global Climate Change’, “Human activities do not control all greenhouse gases, however. The most powerful greenhouse gas in the atmosphere is water vapour, he says, “Human activities have little direct control over its atmospheric abundance, which is controlled instead by the worldwide balance between evaporation from the oceans and precipitation.”
As such, Shaidurov has concluded that only an enormous natural phenomenon, such as an asteroid or comet impact or airburst, could seriously disturb atmospheric water levels, destroying persistent so-called ‘silver’, or noctilucent, clouds composed of ice crystals in the high altitude mesosphere (50 to 85km). The Tunguska Event was just such an event, and coincides with the period of time during which global temperatures appear to have been rising the most steadily – the twentieth century.
Shaidurov’s theory, of course, flies in the face of the more widespread view that the Industrial Revolution of the past 200 years, during which human society unleashed tons of carbon dioxide from the burning of fossil fuels, has triggered the global warming that most scientists believe is underway. Shaidurov says, however, that global temperatures were trending downward prior to a period between 1906-09, a few years before the explosion.
It seems strange to me that an event of this magnitude is mostly known only to science fiction and “X Files” fans. Undoubtedly, this is due purely to the remoteness of this part of the world. If such a thing had landed in Ohio, or Paris, our society would be very different. The memory of such a trauma would reverberate across generations.
Whether or not Tunguska can be blamed for global warming, the event demonstrates that nothing can change history faster than a random chunk of debris from outer space.
I’ll leave to another day the policy impact of Shaidurov’s theory. If this is the cause of global warming, can it be reversed? Will the earth’s upper atmosphere “right” itself, given time? Will Kyoto-type programs help? Geological history certainly suggests that the 5,000 years or so of Earth’s history during which mankind established civilizations and evolved technology has been a period of atypically good weather. Is our luck about to run out? Can our technology help us adjust to what might be an inevitably transformed environment?