If all of the polar ice caps melted

[sylas]

That sounds dubious to me. If the land is already above sea level and then rises, it would have no effect whatever on sea level. Would the land really rise? Last year some workers drove a truck on my lawn to cut down a tree and the ruts are still there.

It's called "isostatic rebound", and it is certainly real. It makes a big difference for the water line on a land mass that rises after having a large ice mass removed, but that is because the land is moving, rather than the ocean. I don't think it would have much effect for sea level on other continents; what is more significant is simply the extra water from the ice going into the ocean.

Cheers -- sylas

 

[Andre]

The melting of the arctic has been of concern before.

‘It will, without doubt, have come to your Lordship's knowledge that a considerable change of climate, inexplicable at present to us, must have taken place in the Circumpolar Regions, by which the severity of the cold that has for centuries past enclosed the seas in the high northern latitudes in an impenetrable barrier of ice, has been during the last two years greatly abated. This affords ample proof that new sources of warmth have been opened, and give us leave to hope that the Arctic Seas may at this time be more accessible than they have been for centuries past, and that discoveries may now be made in them, not only interesting to the advancement of science, but also to the future intercourse of mankind and the commerce of distant nations.’

President of the Royal Society, Minutes of Council, Volume 8. pp.149-153, Royal Society, London. 20th November, 1817.

 

[Andre]

I have been wondering about available long term data of arctic temperatures comparing the warmer spell in the 1940s with those of nowadays. So I went to GISS

http://data.giss.nasa.gov/gistemp/station_data/

and clicked on Northernmost Siberia, Greenland and the NWT in Canada, then I selected the first series of stations that were providing data as of at least 1930 until now. Now what would be the difference between the 1930-40s warming and the current warming?


http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222208910006&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222208910006.1.1/station.gif
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222230740000&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222230740000.1.1/station.gif
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222245070006&data_set=1&num_neighbors=1
http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222245070006.1.1/station.gif
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222234720005&data_set=1&num_neighbors=1
http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222234720005.1.1/station.gif

http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222206740006&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222206740006.1.1/station.gif
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=222242660006&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.222242660006.1.1/station.gif
-----
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=403719250005&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.403719250005.1.1/station.gif
http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=403719380005&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.403719380005.1.1/station.gif
Jan Mayen
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.634010010003.1.1/station.gif

http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=431043600000&data_set=1&num_neighbors=1
http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.431043600000.1.1/station.gif

http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=620040630003&data_set=1&num_neighbors=1
[URL][PLAIN]http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.620040630003.1.1/station.gif

 

[kldickson]

It doesn't need to be. All you need is for the ice to be resting on rock. If so, then melting ice will raise sea level, because the ice surface is above sea level, and it isn't floating.

I know. I was responding to whoever insinuated that the rest of Antarctica was above sea level.

 

[sylas]

I have been wondering about available long term data of arctic temperatures comparing the warmer spell in the 1940s with those of nowadays. So I went to GISS

http://data.giss.nasa.gov/gistemp/station_data/

and clicked on Northernmost Siberia, Greenland and the NWT in Canada, then I selected the first series of stations that were providing data as of at least 1930 until now. Now what would be the difference between the 1930-40s warming and the current warming?

You are looking at regional data, and so you need to be considering regional causes and effects. There's a good discussion of the trends in the Arctic and their credible causes given in the thread [thread=306202]Only dirty coal can safe the Earth[/thread]. (The thread title is a poor attempt at humour; the content of the thread and of the research being discussed is more sensible.)

As I noted previously, this is not the same as the global trend; it is at present much stronger, and so there are additional factors at work in this region which don't apply across the whole globe, and which apply on top of the larger overall global trend to increasing temperatures.

The NCSI site that Evo introduced also has a http://nsidc.org/arcticmet/, which walks through some of the particular factors that pertain to the Arctic, though it doesn't specifically go into the timeline of the 20th century, like the Drew Shindell paper discussed in the thread cited above.

You mentioned also reports from 1817 of Arctic observations; which may relate to movement out of the so-called "little ice age". But there's little doubt that the ice levels then were much greater than now; the period of 1700 to 1800 seems to have been a period of maximum ice; and so that report is about right for moving out of that period.

Recent attempts to look at a history over the last 800 years have been published in "Climate Dynamics". See:

• Macias Fauria, M, A. Grinsted, S. Helama, J. C. Moore, M. Timonen, E. Isaksson, and M. Eronen (2009) Unprecedented 20th century low values of sea ice extent in the Western Nordic Seas since A.D. 1200. Climate Dynamics doi: 10.1007/s00382-009-0610-z. (pdf available http://www.ulapland.fi/home/hkunta/jmoore/pdfs/Macias-Fauria_2009_ClimDyn.pdf ).

From the abstract:

The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid-eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Moderate sea ice extent occurred during thirteenth–fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at *50–120 year. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.​

So there certainly are cycles and variations in the Arctic; but the current reduction in ice cover is exceptional, and not part of a regular short term cycle. Note that the research is not saying 800 years ago is like today. It isn't. The 800 years is rather the bound of time considered.

There's also some useful but less technical information in the NSIDC FAQ, on http://nsidc.org/arcticseaicenews/faq.html#presatellite, which mentions the warmer period in the 1930s and 1940s, but back to the 1800s the data is indirect. The reports you mention are not comprehensive surveys that in themselves allow an easy comparison with current conditions; for that you need research such as the paper I've cited above.

I suggest we ask this thread be moved into the Earth science forum. Now that we are getting a bit technical, it really belongs there, rather than in "general discussion".

Cheers -- sylas

 

[Count Iblis]

If you have mountains, hills etc. that have been underneath ice for a long time and all that ice suddenly melts, they can be unstable and just crumble and fall into the sea, triggering tsunamis.

I think that Britain was hit by such a tsunami 8000 years ago caused by a landslide in Norway.