Monday, 16 February 2009

Musing on sea level rises

A friend of mine is presenting about climate policy this week, and
wanted some visuals about sea level rises under climate change

Current estimates of total sea level rise are for 2 metres in 100 years
- from all sources in both hemispheres. Will Steffen at ANU has gone on
record saying that, although unlikely, a 4 metre rise cannot be ruled
out; Jim Hansen is saying similar things.

Yet it can be hard to get people to realise the severity of a 2 metre
change. Most westerners are pretty OK (apart from some people in
beachfront suburbs) and have the money anyway to build levees, etc.

The web site has a great mapping tool, but an
average 2 meter rise missed the real danger - tidal surges.

Greater expected volatility of weather means we get bigger tidal surges.
When you combine these with a 2 metre rise in sea levels, you get a lot
of coastal flood stories, with the world's big deltas being regularly
covered in salt water. That will lead to food disasters, as some of the
world's great food bowls are deltas (Nile, Red River, Mekong, Yangtze,
Indus, Ganges/Bramaputra) meaning a disproportionate number of people
are exposed to a small change in sea levels. It is true that we may be
able to adapt crops to more saline conditions (a great hope), but lots
of the deltas will be flooded too frequently for even that.

Plus a lot of big cities will get flooded regularly. Even in London one
forecast is that the Thames Barrier will be breached by 2030, flooding
large areas of East London (and thousands of dwellings have been allowed
to be built behind the Barrier on the basis that they are now protected
from flooding risk!). Translate that to calamities in Guangzhou,
Shanghai, Nanjing, Tianjin, Saigon, Kolkotta, Chennai, Mumbai, Lagos,
Miami, New Orleans - 140 million people just there - and we have some
big disaster issues.

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