Mega tsunamis are just "tip of the iceberg", real problems follow.
Beware the quietly thawing North Sea gases
The relationship between rapid global warming and mega-tsunamis would not be the simplistic cause-and-effect sequence outlined by Paul McCrory (16 February p 54), but a feedback loop. McCrory suggests the giant waves could disturb methane hydrate deposits on the seabed and release methane, which is a greenhouse gas. However, the initial rise in global temperature would trigger "outgassings" from frozen methane hydrate deposits, which in turn would accelerate the warming, and so on until the critical temperature was reached that thawed out the bulk of methane deposits--at which point we could expect a runaway greenhouse effect.
There may be some evidence of a truncated sequence like this in the record of tsunami strikes on the east coast of Britain since the last ice age. These were caused by the Storegga slides off the west coast of Norway--large-scale disruptions of the bed of the Norwegian Sea between 11,000 and 8000 years ago that were probably triggered by hydrate outgassings as a result of rising sea temperatures. These outgassings, which were probably not localised, were followed by the prevailing mild climate of the Bronze Age. On average it was 3 °C warmer over Britain than today. However, it would be very difficult to establish a causal link after this time.
If the Storegga slides were to reoccur today they would inundate the entire British east coast from the Shetlands to Norfolk, as well as most of the Netherlands. This is a salutary reminder that the consequences of global warming may not be gradual.
Attention has been focused on the long-term threat to the south coast from mega-tsunamis originating in a volcanic cataclysm at La Palma, but a more immediate threat--only decades, not centuries off--may lie to the north, in the quietly thawing gases beneath the North Sea.
newscientist.com |
