Greenland melt accelerating rapidly 11 August 06

but they didn’t have modern civ then to make it happen really really fast.

How much faster are things happening than in previous periods of global warming & Greenland ice melt? I have this sinking feeling that scientists are so busy counting the molecules on the head of a pin, they aren’t grasping the whole situation. It’s not just the GHGs & warming, but it’s also the very fast rate of GHG emissions & warming. (I have the impression that things happened over centuries & millennia that are happening now over decades.)

Any ideas about what science might say that might be different this time because of such fast rates.

This is yet another confirmation of how our planet’s in danger, but do we wake up? It doesn’t seem so, people still drive their Chelsea tractors and fly somewhere just because the ticket costs £10, not because they have a desire to go there, nor do they know the town/country they are going to. How do we stir them before it gets too late?

“but the last two winters have also been very dry and quite cold, perhaps reflecting the influence of this meltwater in weakening Britain’s rain-bearing westerly winds.”

I’m not sure about the cold bit. Last winter was cool in England & Wales, but only March saw lower than average temperatures in Scotland. The previous winter was actually quite warm, and although England (especially the South) was dry, Scotland was if anything even wetter than usual. See the Met office Stats for England and Scotland.

You might like to have a look at the most comprehensive report of the North Atlantic maritime weather and climate in recent years, particularly at the summary.

http://www.ices.dk/pubs/crr/crr280/CRR280.pdf

The report shows that (contrary to public perception) the trend over the last decade has been for increased sea-surface temperatures and increased salinity in the upper North Atlantic. This, of course, is not what most one would imagine for a weakening of the thermohaline circulation. Note, however, that the ICES teamp looked at different things from the Bryden team (the one that found evidence for an apparent weakening of the circulation). Bryden’s team measured water currents in the sub-tropical North Atlantic.

I know one of the people who worked on the ICES report and asked her about this, but she says that there is far too little long-term information to be clear as to what is going on with the thermohaline circulation – the only certain thing is that there are rapid and massive changes in Arctic waters.

The report also contains a good discussion of the recent trends in the North Atlantic Oscillation, which really largely determines our winter weather. Again, there are no absolutely clear trends (very negative in the 1960s, extremely positive in the late 80s/early 90s, mainly positive since then, but less so. Mark’s reference to a cold and dry winter in 2004/05 is born out for the whole of Western Europe (colder conditions, less westerlies).

I understand that it is not actually clear in how far the North Atlantic Oscillation is linked to sea-surface temperatures, as opposed to stratospheric conditions.

Almuth Ernsting

an excellent link!

In trying to make sense of these trends, I have a few questions for anyone who can answer them. I try to think in terms of what are the dynamic processes behind the observed trends. This how I best understand them.

Does the increase in salinity result from more evaporation due to higher SSTs, less flow of fresh water from land and ice, or because less rainfall is diluting the surface waters?

My bet it is from more evaporation since ice melt is higher and it seems higher SSTs cause more evaporation. I also wonder if the atmosphere is drawing more moisture from the sea because it is warmer and can absorb more water vapor. I am not sure if this capacity to hold more water results in more precipitation over the ocean or less.

Is the warming of the northern oceans offsetting the increase in salinity thereby slowing the thermohaline currents anyway? I ask this question because it is both the salinity and the lowering of the ocean SSTs which drive the current. I wonder if a lower temperature drop offset salinity increase which accounts for the measured slowing of the thermohaline current.

Another question has to do with a steeper ocean temperature gradient. If the surface warming is going down to lower depths, then how does this gradient affect the observed flow of the thermohaline current?

Finally, is there anything from these new discoveries which might modify GW GCM modeling or future trends from GW different from earlier assessments?