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Tuesday, 8 September 2009

We had joy, we had fun, we had seasons in the sun

Politicians heading for the next climate conference will be disappointed to hear that the pinup girl of the climate change world, the Maldives will not be attending. President Mohamed Nasheed of the photogenic country has said his nation will only go to the December talks in Copenhagen if someone offers to pay for the trip. No doubt, someone from the DFID or similar will be on hand to stump up the cash because the plight of the Indian Ocean islands is central to the cause.

The Maldives consists of a group of atolls about seven hundred kilometres south-west of Sri Lanka. The twenty-six atolls encompass a territory featuring 1,192 islets, of which two hundred islands are inhabited. The Maldives is the lowest country in the world, with a maximum natural ground level of only 2.3 metres with the average being only 1.5 metres above sea level, and is thus prone to flooding from global warming.

Woah! Hang on a minute, before we buy into all this guff let us look a little harder. Global warming studies on the Maldives make for attractive colour magazine inserts, but let's look a little harder at what is going on here. 1,192 islets all sticking between 0m and 2.3m out of the sea, surrounded by an ocean that falls away to a depth of a few thousand metres.

Coincidence? Not at all, because the islands sit upon coral reefs that push the land upwards. Upon occasions, storms and tsunamis hit the islands with large waves that will wipe every thing away, which explains why the land is no higher than 2.3m above the sea across the entire 100 square miles of the territory. If that doesn't sound flat, that is the same as the height difference across Lords cricket ground which is about 0.01 square miles and is supposed to be flat.

So whatever natural forces have created the Maldives, they seem to be quite powerful, and absent any radical changes, the presumption is that the natural equilibrium would be preserved over time. With so many islands at just a few metres above the level of the sea, it seems clear that the biosystem is able to adapt to any rising sea level.

What about the massive changes in the Arctic and Antarctic ices shelves which are melting away and will drown us all? Not so fast Mr Anti-Archimedes, those sea ice shelves are floating in the water and has been well understood since the third century BC, but not by global warming alarmists, they displace their own mass of water, and hence when they melt there are no changes in the volume of water, apart from minor, n-th order differences due to changes in salinity that are too small to mention.

Sea levels will only rise when ice sheets resting on land start to melt or the sea expands faster than the rest of the earth due to warming. The Antarctic land based ice sheets are formed by precipitation and as it is still likely to remain cold over the south pole we can expect thet to continue. Indeed with global warming we would expect more moisture in the air and hence more precipitation and a thickening of the ice at the poles, from whence it slides slowly to the shores. Climate change alrmists say that the disappearance of sea ice shelves will mean that the land based glaciers will flow more quickly to the sea, but the accretion of ice at the South POle suggests that we have someway to go before we have a net outflow of ice from over Anarctice land.

But going with the worst estimate of the alrmists, assume that we have an average 60cm rise in world sea levels by 2100 as they predict. Doesn't that swamp the Maldives, despite their apparent ability to adjust to the prevailing sea level? After all, if the land is on average 1.5m avove the seas, then losing 0.6m would probably be terminal.

No, that is more more bad science. An analysis of the geometry of the earth shows that the Maldives lie at a depression in the geoid surface of the earth, in fact at one of the deepest depressions, even though it lies in the middle of the ocean. You probably thought the earth is mostly spherical, squashed at the top and with some lumpy bits called mountains. You might think that the rest of the earth was pretty much regular, particularly the sea which is flat apart from the waves?

Apparently not. The part of the Indian Ocean where the Maldives sit is about 100m below the regular geoid, and that depression is caused as best as we can tell, by very high reates of evaporation of the sea. You read that right. 100m. The fact that the temperature in the area is say around 45 degrees above the melting point of ice means that the rate of evaporation causes a 100m depression in the shape of the ocean. Compare that with the 60 cm sea level rise supposed to happen if the ice caps melt.

So the real risk to the Maldives is not the melting of ice fields 6,000 km away, but the rate of evaporation of the sea around the atoll. In the extraordinarily unlikely event that the sun was switched off, the islands would be 100m under water.

In fact, if the world is heating up, if you remember the Clausius–Clapeyron relation in physics from school you might remember that there is a vaguely exponential increase in vapour pressure with temperature, so we could reasonabley expect to see expect more evaporation with higher temperatures. Indeed if say and average temperature of 40 degrees above the melting point of water leads to a 100m depression in the geoid, an extra 1 degree of temperature might be expected to distort the geoid by more than (100/40 =) 2.5m because of this exponential relationship, although there are clearly other factors at play. But anyway we shouldn't be surprised if sea levels decline in the Maldives.

And lo and behold, that is what has happened. In the last 30 years the sea level has actually fallen by 30 cm, and geological records indicate that in colder times 3,000 years ago the inhabitants of the island survived sea levels that were 50-60cm higher.

My guess is that newspapers, if they still exist in the future, will be paying for bikini clad models to go on photoshoots in the Maldives well past 2100.


Demetrius said...

There have been a couple of walloping earthquakes off Sumatra very recently. Something is shifting down below in the Indian Ocean, but then there always is. Who knows what can happen?

Alex said...

I think you have hit the nail on the head their Demetrius. Superficially the Maldives look precarious, and the idea that they look as though they would be swamped by melting icebergs is superficially persuasive. But the more you look at it (a) the 100+ islands aren't sticking out of the see by less than 3m purely by chance, and in the whole scheme of things a whole metre of water from the icebergs is neither here nor there when you look at the scale of effects that combine to make the Maldives where they are today.