Is sea level rise nonlinear?

[thidmir]

According to the UN panel, sea level rise was supposed to be about 6 inches per decade, but it seems a linear trend was suggested. However, if you look at past ice ages sea level rise could have been about 100 m, ofcourse it might be less if only a part of the artic and antartic zones are thawed, but could this be nonlinear? In other words, could sea level rise due to global warming be linear for the first degree or two and then accelerate?

[swansont]

That's an average. The rise is not linear in time and will also vary geographically.

 

 

 

[MigL]

Melting ice that is 'floating' ( Arctic ) does not cause sea-level rise, but melting ice over land masses ( Antarctic and other glaciers ) will.
IOW, it will not be linear.
 

Edited October 4, 2022 by MigL

[thidmir]

I find it strange since the projected sea level rise by 2050 is 10 inches, which suggests a linear trend, but if it is nonlinear it should be much higher. Is there a mistake here?

 

Santosh Gupta

[swansont]

10 minutes ago, thidmir said:

I find it strange since the projected sea level rise by 2050 is 10 inches, which suggests a linear trend, but if it is nonlinear it should be much higher. Is there a mistake here?

 

Santosh Gupta

Looking at an average, and looking at it annually makes it look linear. Plus the rise has been smaller in the past, which points to an accelerating trend.

If you look at the graph here

https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level

you can get a linear trend out of it, but that would ignore the flat stretch from ~1915-1930 and the slight concavity of the graph. The future will likely have a similar character to it, but with an increasing slope if nothing is done to arrest warming.

10 inches is ~250 mm, which we got over 140 years on that graph, and if that's expected in the next 25-30 years, it's definitely not a linear trend.

 

[studiot]

It is also worth noting that 'sea level' is not flat.

The Pacific is about 400 mm higher than the Atlantic and the Indian is about halfway between.

https://oceanservice.noaa.gov/facts/globalsl.html

Edited October 4, 2022 by studiot

[Ken Fabian]

11 hours ago, thidmir said:

According to the UN panel, sea level rise was supposed to be about 6 inches per decade, but it seems a linear trend was suggested. However, if you look at past ice ages sea level rise could have been about 100 m, ofcourse it might be less if only a part of the artic and antartic zones are thawed, but could this be nonlinear? In other words, could sea level rise due to global warming be linear for the first degree or two and then accelerate?

There are big uncertainties and the IPCC reports do include mention of them. The sea level rise from thermal expansion is linear with respect to ocean temperatures and those do follow air temperatures but ice sheet melt (Greenland and Antarctica mostly) has high potential for non-linear contributions. The (average) rate of rise is currently a lot less than 6" per decade but it is accelerating. Places like the US Gulf of Mexico coast is running about twice the global average. Counter-intuitively the sea levels are falling closest to where land based ice has been lost, mostly Greenland so far, due to lowered local gravity from the loss of mass. This NASA video showing sea level changes (based on satellite data) shows this effect -