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This is a piece taken from the Wikipedia page for the Jason-1 satellite used to measure sea level rise.

Although the 1993–2005 Topex/Poseidon satellite measured an average annual Global Mean Sea Level rise of 3.1 mm/year, Jason-1 is measuring only 2.3 mm/year GMSL rise, and the Envisat satellite (2002–2012) is measuring just 0.5 mm/year GMSL rise.

This would show that either the sea level rise is slowing down or that satellites can not accurately measure the sea level if they are showing completely different readings.

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    I love the people who try to claim that something isn't serious because "the rate of increase has slowed down". A man falling from a cliff will find that after a bit the rate of increase of his downward speed slows down. Doesn't mean he isn't going to hit the ground. – DJClayworth Jul 20 at 21:32
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    @DJClayworth: Your point is a good one in some cases. However, in your example you talk about the "rate of increase of his downward speed", or his acceleration. The OP is asking about a velocity decrease (mm/year). If true, this is indeed good news because it is trending towards a zero sea level rise/year. The correct analogy is that the velocity of a falling man is decreasing. – James Jul 22 at 11:36
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    @JMac: It's true that the "change in yearly sea level rise [is] equivalent to acceleration", but the point is that this acceleration is negative (according to OP's reference). If true and if the trend continues, then soon the sea level will be dropping and we will enter a new ice age. I'm not saying I think this is happening. I'm saying that if the OP's reference is correct, then it would have significant ramifications. Going back to DJClayworth's analogy, if the falling man is in fact decelerating then he may not hit the ground after all. – James Jul 22 at 14:27
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    @James The point is that just looking at a current trend doesn't give you enough information to determine if things are okay or not. That seems to be DJClayworth's point. If OP's reference is correct, it might have significant ramifications; but just looking at the current trend wont tell us how far away the ground is and how fast we are going to hit, as it were. – JMac Jul 22 at 14:32
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    @James: The conclusion, that a negative acceleration leads to a dropping, isn't forcing. A rise might develop like 4, 2, 1, 0.5, 0.25mm/y with negative acceleration, but infinite rising, though. – user unknown Jul 23 at 8:58
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It looks like the Wikipedia page could stand to be updated. If you look at the accumulated global-mean-sea-level data for all the altimetry missions (there are data for 9 of them listed), you can see that the values determined by different missions operating at the same time are consistent within about a 1.5 cm range, and all the missions together show a fairly steady 3.3 mm/yr sea level rise. Since that value is smaller than the variation between measurements across missions, and since the date range of each mission varies, it is natural that the rate of change seen in the data for a single mission might vary as opposed to another mission, but taken together the satellite data give a consistent picture.

The quoted text from the Wikipedia page, in any case, seems to exaggerate the difference between the cumulative rates measured by the specific missions it names. The referenced site gives 2.95 mm/year for Json-1, and 2.49 mm/year for Envisat.
Json-2 was active from 2008-2017 and showed a rate of 4.42 mm/year.

To sum up

  • Cumulative satellite data provides no indication that mean-sea-level rise is slowing down.
  • Satellite sea-level data is noisy but consistent enough to be useful, especially when combining data from multiple missions across decades.

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