Comment by ash | Hacker News Reader

Comment by ash | Hacker News Reader

> In the worst-case scenario, in which sea levels rise by six feet by 2100, ...

Where does six feet come from?

It seems very suspicious. It contradicts NOAA Sea Level Trends data of tide gauge measurements, going back to 1930 and sometimes earlier. According to the map, in almost all places in US the projected sea level trend is no more than 1-1.5 feet by 2100:

https://tidesandcurrents.noaa.gov/sltrends/sltrends.html

What is more, the trend is clearly linear from the start of the measurement. The trend hasn't changed in recent years.

For example, see data from the gauge in Sandy Hook, New Jersey, from 1932: "The relative sea level trend is 4.09 millimeters/year with a 95% confidence interval of +/- 0.2 mm/yr based on monthly mean sea level data from 1932 to 2018 which is equivalent to a change of 1.34 feet in 100 years."

https://tidesandcurrents.noaa.gov/sltrends/sltrends_station....

Gauge in Lewes, Delaware, data from 1919: "The relative sea level trend is 3.48 millimeters/year with a 95% confidence interval of +/- 0.23 mm/yr based on monthly mean sea level data from 1919 to 2018 which is equivalent to a change of 1.14 feet in 100 years."

https://tidesandcurrents.noaa.gov/sltrends/sltrends_station....

There's a major research initiative taking place right now into Thwaites Glacier, as unexpectedly fast melting is occurring. It's thought this is due to warm saltwater penetration underneath the glacier but other factors are being considered.

The issue with Thwaites Glacier is it has a tapered edge that generally resists thawing, but that widens out to a huge contact surface area once erosion by salt water progresses.

This glacier alone will cause a global sea level rise of three feet.

https://thwaitesglacier.org/

> This glacier alone will cause a global sea level rise of three feet.

Where did you get that information? This source from Wikipedia says it would cause a rise of 4 inches:

At the beginning of 2020, researchers from the ITGC took measurements to develop scenarios for the future of the glacier and to predict the time frame for a possible collapse: The erosion of the glacier by warmed ocean water seems to be stronger than expected. The researchers noted with concern, that at the baseline of the glacier, the temperature of the water is already more than two degrees above freezing point. They confirm thawing of the Thwaites glacier contributes about four percent of global sea-level rise. The collapse of this glacier alone would raise the sea level by about 65 centimetres (25 inches).[25]

What?

Your quote says 4% of global sea level rise from this one glacier, not 4" - it says 25" at the end there.

And right next door is a nice mantle plume heating things up. [0] You may have the causality wrong - mantle heats water melts ice - might be the more accurate causal links.

[0] - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...

As a general observation, it's not that useful to look at single gauges. As glaciers melt, the land nearby rises because of the lower weight on it, which shows up as the sea level going down. This is besides all other kinds of geological activity that might be going on in a particular location.

[edit] Anyway to be more specific, there's a single Antarctic glacier with enough water to cause 0.5 meters of sea level rise, and a recent measurement shows it will melt in "decades, possibly more than a century." https://www.bbc.com/news/science-environment-51097309

You can’t just eyeball these graphs and assume the trend is linear: https://tamino.wordpress.com/2019/10/09/sea-level-accelerati...

See also https://tamino.wordpress.com/2019/10/14/sea-level-accelerati...

Mate, you're trying to contradict NOAA government data with someone's blog.

No, I’m not. The NOAA site does not posit that the underlying trend is linear over the period - it simply displays a linear fit on the graphs. See here for more details https://tamino.wordpress.com/2018/04/16/recent-sea-level-cha...

> The long-term linear trend is also shown, including its 95% confidence interval.

I hope you'll forgive the reader for interpreting this as them positing that the trend is linear.

They’re forgiven - but if you’re saying NOAA are saying the trend is linear and will continue to be you’re wrong. All the site is saying is it displays the “average” trend over the period as a straight line. It’s a comment on how the data is presented, not on the underlying dynamics.

From NOAA web site, when you click on "Previous RSL Trends" button:

> Although the trend may vary with the end year, there is no statistically significant difference between the calculated trends if their 95% confidence intervals overlap. Therefore, the most recent calculated trend is not necessarily more accurate than the previous trends; it is merely a little more precise. If several recent years have anomalously high or low water levels, the values may actually move slightly away from the true long-term linear trend.

I was looking for the same, it appears to come from (or be reflected) at least here:

https://cpo.noaa.gov/sites/cpo/Reports/2012/NOAA_SLR_r3.pdf

Where a SLR of 2m by 2100 is reported as an extreme scenario, presumably (but I can't find it in the text) with very low confidence. They give the following definition of the reasons for the low confidence rating, though: "Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts".

Sure, the trend is “clearly” linear until it’s not. Hell a hockey stick chart is mostly two linear trends stuck together. A sigmoid is too.

Most of your comment is flat-out false. That page shows current instantaneous sea level change; it doesn't show future predictions (except in, say, the paper linked at the bottom about predicted sea level change). Sea level rise is increasing each year and is projected to continue increasing faster each year, the rate dependent on how much CO2 we keep putting into the environment.

2m in sea level rise is roughly the current "intermediate" scenario, which would happen if the world made immediate and large reductions in CO2 emissions. That is, we're on track to be worse than that now.

Since I've seen this exact error on HN before (don't recall if it was you who made it or not): do you understand that giving the 2018 sea level rate change as "1.34 feet per 100 years" is NOT a prediction that the sea level will change 1.34 feet over the next hundred years?

> 2m in sea level rise is roughly the current "intermediate" scenario

What is the basis for 2 m prediction?

> giving the 2018 sea level rate change as "1.34 feet per 100 years" is NOT a prediction that the sea level will change 1.34 feet over the next hundred years?

Global 0.3 m rise is among the possible scenarios.¹ And this scenario is consistent with historical measurements. Also note that CO2 level has been rising for the last 60 years. Sea level trend stayed the same compared to the period before industrial CO2 rise.

¹ https://tidesandcurrents.noaa.gov/publications/techrpt83_Glo...

NOAA says "most probably x", you turn that into "no more than x". That's not a fair and honest represntation of that the NOAA says.

Well, considering that global CO2 emission has been steadily increasing [1], and sea level rise tends to follow CO2 level, it's very unlikely that it will continue to increase linearly...

[1] https://www.epa.gov/ghgemissions/global-greenhouse-gas-emiss...

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