From Hadrian Jeffs
Norwich
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.
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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.
