arctic melt

[chilly]

Dear All

A quick question, if as it mentions on the bbc website this morning that the Arctic all year around ice will disapear rapidly in the next few decades, will the flood of fresh water into the sea have an effect upon the NAO which could possible switch it of or at least disrupt it enough to plunge northern Europe into an ice age?

Thanks

Steve

[Stratos Ferric]

:unsure: Dear All

A quick question, if as it mentions on the bbc website this morning that the Arctic all year around ice will disapear rapidly in the next few decades, will the flood of fresh water into the sea have an effect upon the NAO which could possible switch it of or at least disrupt it enough to plunge northern Europe into an ice age?

Thanks

Steve

It depends what melts. The latest report is actually for sea ice (the land ice may remain). At present the ice floats on the surface of the ocean and and depresses the water, forcing it to rise elsewhere away from the ice. Imagine, as an analogy, filling a bucket with water and then lowering that bucket into a half full bath. The level of the bath will rise, right up to the point at which the bucket is fully immersed, but thereafter emtyping the bucket into the bath would make no difference.

Yes, there is ice above the level of the ocean surface, so you might argue that this, if melted, would increase sea level; on the other hand ice floats because it is less dense than the liquid form of water (a property that, as I recall, is unique to water), so the volume occupied by the ice once melted would be less, in any case, than the volume of water actually displaced by the ice. Therefore, if the top of the ice was level with the ocean surface melting ice would actually REDUCE sea level. For this reason there's likely to be "swings and roundabouts", and the net effect of melted ocean ice would be marginally positive.

[chilly]

It depends what melts. The latest report is actually for sea ice (the land ice may remain). At present the ice floats on the surface of the ocean and and depresses the water, forcing it to rise elsewhere away from the ice. Imagine, as an analogy, filling a bucket with water and then lowering that bucket into a half full bath. The level of the bath will rise, right up to the point at which the bucket is fully immersed, but thereafter emtyping the bucket into the bath would make no difference.

Yes, there is ice above the level of the ocean surface, so you might argue that this, if melted, would increase sea level; on the other hand ice floats because it is less dense than the liquid form of water (a property that, as I recall, is unique to water), so the volume occupied by the ice once melted would be less, in any case, than the volume of water actually displaced by the ice. Therefore, if the top of the ice was level with the ocean surface melting ice would actually REDUCE sea level. For this reason there's likely to be "swings and roundabouts", and the net effect of melted ocean ice would be marginally positive.

Thanks SF

[jethro]

I know the net volume wouldn't change drastically, but wouldn't all that fresh water pouring into the ocean have a negative effect upon the Gulf Stream? I thought the big worry was the level of salinity.

[parmenides3]

:unsure: Dear All

A quick question, if as it mentions on the bbc website this morning that the Arctic all year around ice will disapear rapidly in the next few decades, will the flood of fresh water into the sea have an effect upon the NAO which could possible switch it of or at least disrupt it enough to plunge northern Europe into an ice age?

Thanks

Steve

The simple answer is 'no', but the most up-to-date research on this assumes a worst-case scenario of Summer sea-ice loss by about 2080; I'm not sure yet where this new claim of the 2040s comes from. A lot of work has been done modelling the effects of continues Arctic ice loss, and none of the models show a shut down of the North Atlantic Current. Most models do show a degree of slowing, and recent ocean studies suggest that this might be in the order of 10-25% in certain seasons by 2100. Evene if the current slows, though, the surface water temperature is still going to be higher; this is because the cold, fresh water tends to mix vertically into the ocean system. As a result of higher surface water temperatures, atmospheric temparatures are likely to continue to rise, though some localised short-term colling may occur in North Western Europe.

One experiment last year modelled a 'forced' shutdown of the NAC. The amount of freshwater it took is very, very large indeed; because of the way in which water enters and leaves the Arctic, it is very difficult physically to shift the volumes required out of the Arctic into the North Atlantic. The current mainstream opinion in climate science is that a new ice age is not even a remote possibility, though some regional temperature fluctuations are likely.

One the issue of sea-level rise, an important point to remember is that water expands as it warms. If the future melting of the Summer ice-pack is a consequence of warmer oceans, then there will be a thermally-induced sea-level rise.

:)P

[Thundery wintry showers]

It depends what melts. The latest report is actually for sea ice (the land ice may remain). At present the ice floats on the surface of the ocean and and depresses the water, forcing it to rise elsewhere away from the ice. Imagine, as an analogy, filling a bucket with water and then lowering that bucket into a half full bath. The level of the bath will rise, right up to the point at which the bucket is fully immersed, but thereafter emtyping the bucket into the bath would make no difference.

Yes, there is ice above the level of the ocean surface, so you might argue that this, if melted, would increase sea level; on the other hand ice floats because it is less dense than the liquid form of water (a property that, as I recall, is unique to water), so the volume occupied by the ice once melted would be less, in any case, than the volume of water actually displaced by the ice. Therefore, if the top of the ice was level with the ocean surface melting ice would actually REDUCE sea level. For this reason there's likely to be "swings and roundabouts", and the net effect of melted ocean ice would be marginally positive.

That's 100% correct as far as I'm aware; indeed it's one of the main reasons why most scientists suggest that sea-level rises are likely to result not from the melting of polar ice caps over oceans, but rather the melting of continental ice masses and glaciers.