# New study about the rise in global sea levels

#### NTL2009

Here is the BBC article, I've read today.
Conclusion from the original study:

This sounds really alarming to me.
I recently participated in "Hazard Mitigation" studies for two local cities, and since they border the San Francisco Bay, SLR and inundation were part of the studies. ...
Based on the ranges in those studies, what were your ""Hazard Mitigation" action items (I'm curious is all)?

It was surprising to me that it seems within the realm of possibility that ~ 40% of sea level rise is related to human water use, rather than global warming. Yet, we don't seem to hear of that, or actions to take?

#### Sherwood Botsford

Forecasts have been very wrong before. Instead of panicking about a forecast, please provide some data that shows how much change there has been in the last 50 or 100 years. Be sure to provide data that has uncertainties, so that we all can evaluate the situation together.

Truth. The problem with extrapolating from past data is that the same data with uncertainties can fit multiple curves. The advantage of models is that they can give you a basis for 'which curve?' It's still a crap shoot.

In military strategy, you plan not for what you think the opponent will do, but instead plan for what you think he can do. You plan for capability, not intent.

For planning public policy, you plan for worst outcomes, at least to the point where you aren't totally gobsmacked when it happens. FEMA's for Katrina is a good counter example.

Another consideration is the reputation of the forecasters. The IPCC has consistently under reported the situation. Trends have been just beyond their most pessimistic estimates.

Were I in a planning role, I would take the most pessimistic prediction available, and make it 20% worse, and use that as my main scenario. E.g. If now the worst forecast is 6 feet, I would plant for 7.2 to 8 feet SLR.

First tier planning is often cheap. It's a change in policy, change in building codes.

Consider New Orleans. If new construction were on stilts, with the under story used for storage, parking, and a place for the kids to play on a rainy day, then when the evac order comes, the boxes of stuff come upstairs, the car takes people out of town. If the under-space is on a separate subpanel and devices such as furnace and water heater and air conditioner are on the main floor, then the house is habitable as soon as the flood waters recede. Cost: Building code change.

#### berkeman

Mentor
Based on the ranges in those studies, what were your ""Hazard Mitigation" action items (I'm curious is all)?
I think the results of our study/report were two-fold with respect to the rising Bay water levels. First, the results enabled the local cities to apply for additional FEMA funds to increase the height of existing levees, and perhaps adding more of them. Second, it probably will prevent building permits for new home developments in some areas that are expected to be inundated in the future. Good question.

#### russ_watters

Mentor
It was surprising to me that it seems within the realm of possibility that ~ 40% of sea level rise is related to human water use, rather than global warming. Yet, we don't seem to hear of that, or actions to take?
It's probably because that's past sea level rise, not projected future sea level rise.

#### russ_watters

Mentor
Another consideration is the reputation of the forecasters. The IPCC has consistently under reported the situation. Trends have been just beyond their most pessimistic estimates.
Really? I thought we were tracking below their median estimates? Do you have any sources for this?

Staff Emeritus
I'm interested in that too. IIRC, IPCC-1 seems to be a factor of 2 above what we see, and a factor of maybe 4 above what we see given recent CO2 numbers. (It's true that more modern model do a better job of retrodicting)

#### NTL2009

... It was surprising to me that it seems within the realm of possibility that ~ 40% of sea level rise is related to human water use, rather than global warming. Yet, we don't seem to hear of that, or actions to take?
It's probably because that's past sea level rise, not projected future sea level rise.
But wouldn't that be continuing to contribute, probably at an even higher rate (more population, more crops being irrigated)? I can't think of any reason it would hit some sort of equilibrium, or stop altogether.

#### russ_watters

Mentor
But wouldn't that be continuing to contribute, probably at an even higher rate (more population, more crops being irrigated)? I can't think of any reason it would hit some sort of equilibrium, or stop altogether.
If I read it correctly the study said it is because of the pumping of groundwater out of the underground aquifers. In the US anyway we've severely depleted them and have started managing them better to avoid running out. Also, population growth is slowing whereas AGW is accelerating. That said, I don't think I saw a prediction about the future.

I'm not very familiar with this issue though.

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#### votingmachine

To the OP - We humans need to understand that as we come out of the last ice age that melting will continue . Human activity may be accelerating what would happen anyway. We need to realize that just because we planned cities on coasts and like things the way they have been the past couple of generations does not mean that they can or should remain that way. Things always change.

Look at history. Look at all of the cities we are finding under water. Look at the settlements we are finding that were destroyed under glaciers. Look at the sea fossils we are finding at the top of mountains. Where I live now was once a sea. New York City was once under a glacier 2,000 feet high.

We need to accept that we planned and built without understanding the impact that natural climate change would eventually make. Now that it may be speeding up, people are saying that it can't happen?

Anyway, enough of the panic about changes, change will happen. We don't discuss the repercussions of the changes, we only discuss the science if you wish to understand the science behind what is happening.
Your assuming we are along an increasing temperature path currently. As an analogy, if you are in spring and had some fires to warm yourself, the natural temperature the next few weeks is warming from the season change, with the fire contributing little to the months later highest temperature. If you have a fire on the hottest day of the year, you are indeed raising the temperature of that highest temperature.

I find your comment a bit like "in the long run we're all dead". It is true, but hardly useful. I still plan on taking a shower today, even though in 100 years, my walking around stinky is unimportant. I will get my flu vaccine, even though getting sick and dying is largely unimportant historically. I might even bother to eat.

People should not panic about things they cannot change. But they also should not assume they are unimportant and can affect nothing. You may be right ... there may be nothing that humans can do to constrain earth temperatures within a preferred range. But it certainly looks like we could allow more heat to escape earth, and keep temperatures lower. I'm not sure we are as powerless as we once were.

#### Evo

Mentor
People should not panic about things they cannot change. But they also should not assume they are unimportant and can affect nothing. You may be right ... there may be nothing that humans can do to constrain earth temperatures within a preferred range. But it certainly looks like we could allow more heat to escape earth, and keep temperatures lower. I'm not sure we are as powerless as we once were.
If you read my responses I said
It's upsetting, but panic and despair won't help, it will just make you sick, level headed action is the best course if you want to get involved.

Anyway, we're still going off topic.
and
This is the type of common sense things we should be doing to address the changes and how we should adapt.
In response to Berkeman's post

I didn't say that there was nothing that could be done, I said that there were sensible ways to approach the issues. Drastic, panic driven responses by humans have a long history of making things worse. Just look at all of the invasive species we introduced in order to control problems that have created much worse issues.

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#### jim hardy

Gold Member
2018 Award
Dearly Missed
Before i panicked i'd have to go back and check all the 20th century data to see whether it is based on the 1929 or the 1988 sea level datum and if it's all been adjusted to the latter or did the computer plots just smooth out the step change.

I started that exercise once but gave up when i read that around the US gulf coast much of apparent water level rise is due instead to land sinking.

I decided geophysics is not my area of expertise
so now i just dismiss anything related to climate that i sense is trying to arouse my emotions.

old jm

#### Steelwolf

Gold Member
Something that was noted in times past, but the Mississippi delta and the surrounding coastlines have been dropping due to oil extraction for over a century and was rather well documented and pegged to the volume of oil pumped. And places like Jakarta they are having a constant, losing battle to loss of land due to fresh water extraction.

#### Genava

It was surprising to me that it seems within the realm of possibility that ~ 40% of sea level rise is related to human water use, rather than global warming. Yet, we don't seem to hear of that, or actions to take?
There is a review with a different conclusion here: https://link.springer.com/content/pdf/10.1007/s10712-016-9399-6.pdf

It seems that the study from Pokhrel et al. is overestimating greatly the contribution from water use.

To the OP - We humans need to understand that as we come out of the last ice age that melting will continue . Human activity may be accelerating what would happen anyway.
Actually, the Holocene temperatures are cooling for 6'000 years. See the following papers:

Pacific Ocean Heat Content During the Past 10,000 Years

Use this link if you have access
https://science.sciencemag.org/content/342/6158/617

Deep Heating
Global warming is popularly viewed only as an atmospheric process, when, as shown by marine temperature records covering the last several decades, most heat uptake occurs in the ocean. How did subsurface ocean temperatures vary during past warm and cold intervals? Rosenthal et al. (p. 617) present a temperature record of western equatorial Pacific subsurface and intermediate water masses over the past 10,000 years that shows that heat content varied in step with both northern and southern high-latitude oceans. The findings support the view that the Holocene Thermal Maximum, the Medieval Warm Period, and the Little Ice Age were global events, and they provide a long-term perspective for evaluating the role of ocean heat content in various warming scenarios for the future.
Abstract
Observed increases in ocean heat content (OHC) and temperature are robust indicators of global warming during the past several decades. We used high-resolution proxy records from sediment cores to extend these observations in the Pacific 10,000 years beyond the instrumental record. We show that water masses linked to North Pacific and Antarctic intermediate waters were warmer by 2.1 ± 0.4°C and 1.5 ± 0.4°C, respectively, during the middle Holocene Thermal Maximum than over the past century. Both water masses were ~0.9°C warmer during the Medieval Warm period than during the Little Ice Age and ~0.65° warmer than in recent decades. Although documented changes in global surface temperatures during the Holocene and Common era are relatively small, the concomitant changes in OHC are large.

A Reconstruction of Regional and Global Temperature for the Past 11,300 Years

Use this link if you have access
https://science.sciencemag.org/content/339/6124/1198.full

Forecasts have been very wrong before. Instead of panicking about a forecast, please provide some data that shows how much change there has been in the last 50 or 100 years. Be sure to provide data that has uncertainties, so that we all can evaluate the situation together.
There is an article by professor Clint Conrad on the European Geosciences Union's blogs about the accuracy of the previous forecast. Here the link:

How good were the old forecasts of sea level rise?

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#### MikeeMiracle

Most of our historic cities are built near the Sea as transport of goods relied on shipping. Movement of goods from ships to the population centers is trivial if the ports if next to the city. Imagine hundred of years ago trying to move enough goods for a city of 1 millions people any distance.

In this day an age we still rely mostly on shipping but there is nothing stopping us building on higher ground just having our ports at sea level as transportation by road/rail back to the population centers is a trivial concern and easily achievable.

Opinion: Sea levels continue to vary, even without human inteference we will eventually have another Ice Age and another period where all the Ice melts. There is no point in trying to fight nature as we can't win, the best we can do is plan around it so that we are less affected when not if that change occurs.

#### davenn

Gold Member
In this day an age we still rely mostly on shipping but there is nothing stopping us building on higher ground just having our ports at sea level as transportation by road/rail back to the population centers is a trivial concern and easily achievable.
Not every country has higher ground to retreat to !

And so by your way, all/many of the existing ports become unusable and zillions of  rebuilding
new infrastructure that no one ( very few) can really afford to do

#### Genava

Sea levels continue to vary, even without human inteference we will eventually have another Ice Age and another period where all the Ice melts. There is no point in trying to fight nature as we can't win, the best we can do is plan around it so that we are less affected when not if that change occurs.
I don't think it is the question the humanity is facing. Climate change and sea level rise will happen anyway (and is happening now), the question is more about how far we should go in the increasing of the phenomenon. Basically we have simply the control of the thermostat and our decisions will define the temperatures of the next decades and centuries.

#### Evo

Mentor
Ok, I don't want to get involved in this thread, but seriously, there is something that needs to be said here, if it hasn't already. Sea level rise is not the same everywhere, it actually can lower in some areas.

Regional effects cause sea levels to increase on some parts of the planet, decrease on others, and even to remain relatively flat in a few places, including, in recent decades, on the California coast.

On the misnomer of "global" sea level rise.

Understanding trends in sea level, as well as the relationship between global and local sea level, provides critical information about the impacts of the Earth's climate on our ocean and atmosphere. The image above shows sea level change since 1993 and demonstrates the variation globally.

Most people are surprised to learn that, just as the surface of the Earth is not flat, the surface of the ocean is not flat, and that the surface of the sea changes at different rates around the globe. For instance, the absolute water level height is higher along the West Coast of the United States than the East Coast.

You may have heard the term “global sea level,” which refers to the average height of all of the Earth's ocean basins. "Global sea level rise" refers to the increase in the average global sea level trend.

"Local sea level" refers to the height of the water measured along the coast relative to a specific point on land. Tide stations measure local sea level. "Relative sea level trends" reflect changes in local sea level over time. This relative change is the one most critical for many coastal applications, including coastal mapping, marine boundary delineation, coastal zone management, coastal engineering, sustainable habitat restoration design, and the general public enjoying their favorite beach.

#### MikeeMiracle

I was not suggesting that we actively try and relocate everyone, as rightly stated the cost would be stratastophic. Merely that going forward we plan accordingly. Climate change is a global challenge that needs a global response from humanity as a whole. We are all currently silo'd into our own countries and that just does not work for this challenge.

#### Genava

Ok, I don't want to get involved in this thread, but seriously, there is something that needs to be said here, if it hasn't already. Sea level rise is not the same everywhere, it actually can lower in some areas.
Yes sure. It is the same problem than the temperature, regional changes are different than global change in average. This is why you need to look at the whole picture, with global data.

"Sea-level data since 1994, taken by the TOPEX and JASON missions, reveal complex changes in sea level that vary across the globe — but the overall trend is a strong increase."

Here the visualization from NASA: https://svs.gsfc.nasa.gov/11927

#### lucas_

"Greenland lost 2 billion tons of ice this week, which is very unusual"

#### russ_watters

Mentor
There is no point in trying to fight nature as we can't win, the best we can do is plan around it so that we are less affected when not if that change occurs.
If you mean we ultimately can't control the climate on a geological time scale, sure, but we are proving we can control it (currently to our detrement) on a generational scale.

And on a day-to-day scale I'd say we spend the majority of our time and resources fighting nature and mostly winning.

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#### lomidrevo

Opinion: Sea levels continue to vary, even without human inteference we will eventually have another Ice Age and another period where all the Ice melts. There is no point in trying to fight nature as we can't win, the best we can do is plan around it so that we are less affected when not if that change occurs.
The main point is that rapid climate changes that we can observe recently are almost surely driven by human activities, and there is a consensus about that in scientific community, see this article:
Multiple studies published in peer-reviewed scientific journals show that 97 percent or more of actively publishing climate scientists agree: Climate-warming trends over the past century are extremely likely due to human activities.
So the current situation is not about "trying to fight nature". It is the mess that we ourselves have produced that we should fight against. The best we can do (for beginning), is to reduce the emissions of greenhouse gasses (mainly CO2), but we are constantly failing in this task: https://www.iea.org/geco/emissions/

#### MikeeMiracle

To clarify, I was not suggesting the current climate issue are not human induced, neither am I stating that we shouldn't try to reduce our impact as much as possible.

I am saying we should start planning for life away from the coasts in addition to doing everything we can to try and reduce human related warming.

Cities have lifespans in the thousands of years. We now have the technology and foresight to appreciate what might happen in those timescales, why not plan accordingly for the long term future?

#### DrStupid

I am saying we should start planning for life away from the coasts in addition to doing everything we can to try and reduce human related warming.
It is quite trivial that we need to adapt to the changed climate. However, living away from the coasts would include abandoning entire countries. Nobody knows if something like that is possible at all and if yes, how it would impact the rest of the world. At least Netherland prefers to flee forward and supports floating cities instead.

#### Frosted Flake

He who evokes Star Trek in a serious discussion loses.

But...

This discussion smells exactly like ONE Vulcan displaying "intellectual superiority" before a LARGE group of "irrational humans". Not in 'real life', but on TV. FICTIONAL. And not because it makes sense, but in order to illustrate the difference between humans and Vulcans, who understand (sorry, ran out of scare quotes) everything yet seem to care about nothing. Except intellectual superiority. And not because there is any truth behind or reason for it, but rather, as a plot device intended to piss the audience off. I had no idea this forum prohibited discussion of the existential crisis of our times, not nuclear war, no ==> global warming <==. And why? Because ===> it's political <===. As existential crises tend to be...

Oh, for christs sake. (swear, not prayer). I would like a clear headed, Vulcan style explanation of how we are going to solve problems we are not permitted to discuss.

Thank you.

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