3 ms·

I have no issue believing you can measure sea levels at certain places. The question is, how do you mix all those measurements together to determine a global se

I have no issue believing you can measure sea levels at certain places. The question is, how do you mix all those measurements together to determine a global sea level number? Afaik many things affect local measurements, like storms and tides. For example, if you measure at three points in the US, and one point in Japan, how are the measurements weighted? Suppose a storm is blowing in the US, increasing the measurements by 1m. How is it being accounted for?

seszett 7y ago
Well actually, the total amount of ocean water stays constant during a storm. The quantity of rainwater that falls is absolutely negligible, and the surge caused by wind means the water level falls very slightly in the areas that are not affected by the very localized surge. That's why you don't measure "three points in the US and one point in Japan". You measure thousands of points all around the world, so if storms affect two or three of them for a day, the global result isn't significantly affected. For instance, just the French observation network is made up of 90 stations that cover enough of the globe to be enough on their own for measuring a 2 mm rise over two months (near real-time data available on ftp://ftp.sonel.org/tidegauge/rmsl/Demerliac/RAW/). It's really not as complicated as you think it is, the basic science behind global sea level measurements was established in the 18th century.
- xaxsacsdaffbnk 7y ago
  There still has to be some kind of formula to tie all measurements together, and I doubt it is simply a mean. Afaik it is possible that sea levels fall in some places and rise in others. If it was just a mean, it would change for example if you added measuring points to the network. Then you would have to account for that. In the 18th century, they didn't have as many nodes in the network as today. How do they compare today's values to the values from the 18th century?

seszett 7y ago

Well actually, the total amount of ocean water stays constant during a storm. The quantity of rainwater that falls is absolutely negligible, and the surge caused by wind means the water level falls very slightly in the areas that are not affected by the very localized surge. That's why you don't measure "three points in the US and one point in Japan". You measure thousands of points all around the world, so if storms affect two or three of them for a day, the global result isn't significantly affected. For instance, just the French observation network is made up of 90 stations that cover enough of the globe to be enough on their own for measuring a 2 mm rise over two months (near real-time data available on ftp://ftp.sonel.org/tidegauge/rmsl/Demerliac/RAW/). It's really not as complicated as you think it is, the basic science behind global sea level measurements was established in the 18th century.

xaxsacsdaffbnk 7y ago
There still has to be some kind of formula to tie all measurements together, and I doubt it is simply a mean. Afaik it is possible that sea levels fall in some places and rise in others. If it was just a mean, it would change for example if you added measuring points to the network. Then you would have to account for that. In the 18th century, they didn't have as many nodes in the network as today. How do they compare today's values to the values from the 18th century?