My OperaLong Term Sea-Level Changes
Friday, March 7, 2008 4:26:50 PM
Kim at All my Faults are Stress Related has already written a post on a new paper in Science on estimates of global sea level during the Cretaceous period and what National Geographic got out of it. It is good, so just go and read it, and don’t forget to read the comments as well.
What I would like to stress here is the difference it makes, whether we are talking about long term or short term changes, and the importance of the little word “global”.
Kim states that
For the non-geologists among you I would like however to rehearse the possible causes for global sea-level change:
1. On a long term geological scale (i.e. millions of years):
- Plate tectonics (changes in sea-floor spreading rates, collision of continents and changes in ocean ridge lengths).
- Emplacement of oceanic plateaus, so-called large igneous provinces (by many people believed to be caused by so-called Superplumes).
These factors are governing oceanic area and average oceanic depth. They are the ocean basin dynamics treated in the Science paper. These changes, although important, relevant and interesting, are totally irrelevant for the current discussion about global warming or climate change.
2. On a short term scale
- Global temperatures, e.g. through thermal expansion of ocean water and melting of ice cover.
- Variations in water volume of groundwater and lakes.
Global is about global average, which means that some places will have values below the global average and other places have values above the global average. During global warming some places will most probably become colder. I just read about a non-important, but telling, little detail. Over the last 35 years the sea level at Esbjerg, a town at the southern west coast of Denmark, has risen 14 cm. The world ocean average rise, however, was only 12 cm. This small difference of 2 cm is supposed to be due to more frequent westerlies in the North Atlantic Area since 1972. (This higher frequency is probably due to global warming). In the US they are by the way arguing that they have had a winter much colder than normal - well I can assure you that where I live our winter has been extremely mild, with temperatures far above average and nearly as warm as the year before. What we must look at however is not single local exceptions but global trends.
Calculating or estimating the global sea level 65 million years ago is a tricky business. It is dangerous to base the calculations on one specific location (like New Jersey). It is no surprise that the estimates differ enormously (from ca. 40 to ca. 250 metres above the present level).
The burning problem today is that the (short term) change is extremely fast. The long term fluctuations won’t help our children and grand children next century.
• http://shearsensibility.blogspot.com/2008/03/misleading-headline-of-day-sea-level-is.html
• http://news.nationalgeographic.com/news/2008/03/080306-sea-levels.html
• http://www.sciencemag.org/cgi/content/short/319/5868/1357
• http://www.planetark.com/dailynewsstory.cfm/newsid/47376/story.htm
• http://www.abc.net.au/science/articles/2008/03/07/2183231.htm
What I would like to stress here is the difference it makes, whether we are talking about long term or short term changes, and the importance of the little word “global”.
Kim states that
The high sea levels of the Cretaceous are hardly big news to geologists, and the role of mid-ocean ridges in controlling global sea levels was accepted by the 1980's, at least.
For the non-geologists among you I would like however to rehearse the possible causes for global sea-level change:
1. On a long term geological scale (i.e. millions of years):
- Plate tectonics (changes in sea-floor spreading rates, collision of continents and changes in ocean ridge lengths).
- Emplacement of oceanic plateaus, so-called large igneous provinces (by many people believed to be caused by so-called Superplumes).
These factors are governing oceanic area and average oceanic depth. They are the ocean basin dynamics treated in the Science paper. These changes, although important, relevant and interesting, are totally irrelevant for the current discussion about global warming or climate change.
2. On a short term scale
- Global temperatures, e.g. through thermal expansion of ocean water and melting of ice cover.
- Variations in water volume of groundwater and lakes.
Global is about global average, which means that some places will have values below the global average and other places have values above the global average. During global warming some places will most probably become colder. I just read about a non-important, but telling, little detail. Over the last 35 years the sea level at Esbjerg, a town at the southern west coast of Denmark, has risen 14 cm. The world ocean average rise, however, was only 12 cm. This small difference of 2 cm is supposed to be due to more frequent westerlies in the North Atlantic Area since 1972. (This higher frequency is probably due to global warming). In the US they are by the way arguing that they have had a winter much colder than normal - well I can assure you that where I live our winter has been extremely mild, with temperatures far above average and nearly as warm as the year before. What we must look at however is not single local exceptions but global trends.
Calculating or estimating the global sea level 65 million years ago is a tricky business. It is dangerous to base the calculations on one specific location (like New Jersey). It is no surprise that the estimates differ enormously (from ca. 40 to ca. 250 metres above the present level).
The burning problem today is that the (short term) change is extremely fast. The long term fluctuations won’t help our children and grand children next century.
• http://shearsensibility.blogspot.com/2008/03/misleading-headline-of-day-sea-level-is.html
• http://news.nationalgeographic.com/news/2008/03/080306-sea-levels.html
• http://www.sciencemag.org/cgi/content/short/319/5868/1357
• http://www.planetark.com/dailynewsstory.cfm/newsid/47376/story.htm
• http://www.abc.net.au/science/articles/2008/03/07/2183231.htm
You must be 
Ole Nielsennielsol # Friday, March 7, 2008 5:28:00 PM