Global Warming

[ibis]

Assuming we are in a warming period, it follows that there will be an increase in sea level. Not taking into account any dam release of melt water this warming should roughly show a corresponding rise in sea level. We hear all the time of pre-dicted rises of 7m etc in the next 50 years(which is hard for the average man to grasp) but there is no talk of actual rise. Should we not be seeing yearly rises recorded locally? This sort of information would be invaluable to influence public opinion.

Not far to look: accelerating sea-level rise over the last 100 years any use to you?

From 3,000 years ago to the start of the 19th century sea level was almost constant, rising at 0.1 to 0.2 mm/yr.[1] Since 1900 the level has risen at 1 to 2 mm/yr; since 1992 satellite altimetry from TOPEX/Poseidon indicates a rate of rise about 3 mm/yr.

With no further rate rises, that's only 30cm/century - midrange on the IPCC predictions. Ice sheet collapse scenarios such as Greenland (total possible rise 7m) would be more like 140mm/year (ie the current yearly rise happening every 10 days).

Again, the idea that Greenland, like Antarctica, would actually accumulate more snow (thus locking up more water as ice, and balancing the sea-level rise from thermal expansion) under global warming was largely borne out over the last few decades. However, that assumes that the actual ice dynamics remain the same, with similar flow rates, nothing dramatic or new happening - and those are the assumptions built into the IPCC models.

What is not known is whether that is a good assumption. Currently, the breakdown of Greenland ice is faster than predicted - too many crevasses, possible detachment of the glaciers from their bases, etc - and Greenland, like Antarctica, is losing ice mass, not gaining it. This may be a temporary effect before a new stability sets in - or it may not.

[bryannavaro]

Parts of the Antarctic are increasing in ice, other parts are decreasing, because global warming does not impact our planet uniformly. The net effect is definitely an overall decrease in Antarctic ice though. It was predicted by climate scientists that the Antarctic would lag overall global warming slightly, due it being isolated from global climate circulation by the Southern Ocean. Like I said, the scientists have predicted this lag and yet it is being used as a stick to beat them with. The Antarctic will catch up (quite spectacularly) later on this century and next century though. The wheels have already been set in motion. Even if we were to cut worldwide emissions to zero from tomorrow we're committed to centuries of warming already. I don't like that the IPCC predictions only go to 2100 (only 93 years away... there are kids alive now who will live to see it), as the trends are set to continue at pace into the 22nd and 23rd century. I do wish they'd extend their predictions, as that might help wake up some policy makers.

As I mentioned earlier, global warming does not occur uniformly across the planet. The most pronounced warming is predicted to occur at the poles, as is being observed in the Arctic at the moment, with Antarctica to follow later. The new IPCC sea level predictions are too conservative in my opinion, as they do not take (sub)polar land ice losses into account.

[Eddiepops]

Can anyone give me statistics on increase in sea levels due to Global Warming? We are continually been shown of the depletion of Artic ice(I understand about floating ice not increasing sea level), but land based ice, glasiers shearing off and tundra leaking etc. It does seem to me that sea levels should be increasing at a measureable rate..........but yet this info is not there that I can find. We are told that London will be under 35 ft of water in some future year.......but surely this should be gradual. I am not interested in surges. Thanks

Two more things to take into account here - London and the surrounding area is still sinking after the last ice age, by about 1 mm a year, so that adds to the affect somewhat.

Secondly, another element which adds to rising sea levels is thermal expansion, in that as the world's oceans heat up they expand a little bit (a small effect, but globally significant).

[descartes]

Thanks for all the info but it still does not answer my question. Perhaps I am being simplistic but as I see it if we are to believe the science global temperatures are rising in a straight line over time. Therefore sea levels should follow the same line. So therefore for any given referance point I should be able to see a corresponding rise due to global warming. All present info is either looking back or predicting forward. I would like to see an ongoing yearly average shawing the end of my garden. This make sense?

[Fionn_McCool]

I would like to see an ongoing yearly average shawing the end of my garden. This make sense?

Nope... shawing ?

Is this what you mean.

[ibis]

Or this?

[descartes]

Thanks Fionn,
No. I had in mind an annual register of increase in Sea Level that could be referenced locally. So for example if our good planner were to rule on a project that this aspect would be apparent to all by projecting the trend in a straight line, that is assuming a linear co-relation.

[jc]

Perhaps I am being simplistic but as I see it if we are to believe the science global temperatures are rising in a straight line over time. Therefore sea levels should follow the same line.

I don't know if you're being simplistic or not, but I'm curious as to how you come to this conclusion.

Is there actual science behind your sea-level argument, or is it just a "gut feeling" ???

I ask because I could see how a small global temperature rise could lead to a certain amount of ice melting, but with the remainder then reaching a new equilibrium and remainig solid. Subsequent small positive deltas in temperature would have similar effects. Unquestionably, there is some threshold which when crossed would result in steady-state melting without need for a further temp change, but without knowing where that threshold lies, surely we shouldn't assume we're already above it?

[descartes]

Or this?

Thanks Ibis this is what I was looking for.
If this linear projection applies locally, why are we allowing development on flood plains? Is there an allowed development time? i.e. no development where Sea Level will rise within 100 years?

[TheBear]

<Mod>Moved to the Environment forum.</Mod>