quote:
Studies in the 1980s and ‘90s suggested the present-day Earth was safe against a runaway, but a paper published this week in Nature Geoscience argues that “the runaway greenhouse may be much easier to initiate than previously thought.” Indeed, the study suggests that without the cooling effects of certain types of clouds, modern Earth would already be well on its way to broiling like Venus. (Scientific American is part of Nature Publishing Group.)
According to the study’s lead author, Colin Goldblatt of the University of Victoria in British Columbia, the disturbing result hinges less on carbon dioxide and more on humble water vapor, which recent investigations have shown absorbs solar radiation more efficiently than previously believed. “The old answer was that a runaway on Earth right now was theoretically impossible,” Goldblatt says. “Even if you evaporated a big chunk of ocean it would just rain back out, because the water vapor would radiate away more thermal energy than it absorbed through sunlight. Our new calculations show that a water vapor–rich atmosphere absorbs more sunlight and lets out less heat than previously thought, enough to put the Earth into a runaway from which there would be no return.”
The upside of the new study is that even though a climate runaway may be possible in theory, it remains very difficult to cause in practice through human greenhouse gas emissions. “We’ve estimated how much carbon dioxide would be required to get this steamy atmosphere, and the answer is about 30,000 ppm of atmospheric carbon dioxide, which is actually good news in terms of anthropogenic climate change,” Goldblatt says. Thirty thousand ppm is about 10 times more carbon dioxide than most experts estimate could be released from burning all available fossil fuels, he notes, although such high values could in theory be reached by releasing large amounts of carbon dioxide from the Earth’s vast deposits of limestone and other carbonate rocks.
BronDus het lijkt te kunnen als we echt heel dom zijn en nog eeuwen doorgaan met het opstoken van elke koolstofvoorraad die we kunnen vinden maar in de praktijk - waarin regeringen en burgers wereldwijd bewust zijn van de gevaren van sterke klimaatverandering - is dit vrijwel onmogelijk. Gelukkig.
Maar er zijn ook wetenschappers die denken dat het kantelpunt al eerder bereikt kan worden, waaronder de bekende klimatoloog James Hansen:
quote:
if we burn all reserves of oil, gas, and coal, there's a substantial chance that we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome [the runaway greenhouse] is a dead certainty.
Bron: zijn boek "Storms of my Grandchildren" uit 2008
Misschien toch maar beter om de kansen in ons voordeel te keren en het niet uit te proberen, er is immers maar één aarde...