Will the Earth really flood when global warming happens?

[DrClapeyron]

Will the Earth really flood when global warming happens? Seems far from definitive and far less clear than the science behind global warming. I remember my Oceanography professor challenging the notion that global warming would raise sea-level, shut off gulf stream, thermohaline circulation. My professor seemed most skeptical of sea-level rise, perhaps because it is more political than the other possible changes or possibly because it's easier to make a Hollywood picture about sea-level rise than it is about the Atlantic thermohaline current shut down.

 

[vanesch]

I think the worst case predictions for the coming century have an upper bound of about 2 meters (this was written in the Copenhagen update of the IPCC report, discussed in another thread here https://www.physicsforums.com/showthread.php?t=358328 )

That is problematic for some islands - I don't know how problematic that is for most coastal regions, if you throw in some civil engineering like the Dutch are used to.

(Amsterdam lies below sea level).

 

[planethunter]

I honestly think the whole global warming phenomena is overblown. Unless water levels rise dramatically (and I mean hundreds of feet), then I really don't see a major impact on our ecosystems- with the exception on how this will effect coastal animal habitats.

 

[DaveC426913]

I honestly think the whole global warming phenomena is overblown. Unless water levels rise dramatically (and I mean hundreds of feet), then I really don't see a major impact on our ecosystems- with the exception on how this will effect coastal animal habitats.

Considering how much diversity there is in those coastal habitats, as well as how much of the human population lives in those coastal areas, I don't think it's overblown.

 

[D H]

I honestly think the whole global warming phenomena is overblown. Unless water levels rise dramatically (and I mean hundreds of feet), then I really don't see a major impact on our ecosystems- with the exception on how this will effect coastal animal habitats.

You've been listening to too many granola heads. There are wackos on both sides of the global warming debate, and the wackos on the left care more for polar bears and the fragile environment than they do for humanity. The fragile environment is pretty dang robust. (Aside: The sheer number of humans around does a lot more harm to the environment than a few meter rise in sea level will do.)

Our modern society is not so robust. A few meters rise probably will result in significant economic damage.

 

[mgb_phys]

A few meters rise probably will result in significant economic damage.

A 1m rise would make London and Manhattan look a lot like New Orleans (afterwards)

 

[Phrak]

I encourage all believers in a two meter rise in sea level to invest in future beachfront property at discount prices.

 

[wildman]

2 meters would be a bummer in Florida.

 

[fatra2]

Hi there,

It always depends which theory you look at. Some theories (the ones that are really scary) say that the water level will rise way above the MontBlanc in France.

I happened to look at some method that brings everything back into proportions, which states that the Alestch Glacier (the biggest glacier in the Alps) has enough water to barely fill the Geneva lake (89km^3). Therefore, which theory to believe is up to everyone, but we might be blowing global warming and its effect out of proportion.

Cheers

 

[Andre]

Could anybody reproduce that peer reviewed article that claimes two meters?

Is this just written for the trashcan?

Siddall et all 2009; Constraints on future sea-level rise from past sea-level change; Nature Geoscience 2, 571 - 575 (2009) Published online: 26 July 2009 | doi:10.1038/ngeo587 ,

...Our model explains much of the centennial-scale variability observed over the past 22,000 years, and estimates 4–24 cm of sea-level rise during the twentieth century, in agreement with the Fourth Assessment Report of the Intergovernmental Panel on Climate Change1 (IPCC). In response to the minimum (1.1 °C) and maximum (6.4 °C) warming projected for AD 2100 by the IPCC models, our model predicts 7 and 82 cm of sea-level rise by the end of the twenty-first century, respectively...

This is the graph of current sea level rise, issued by the University of Colorado:

How does that compare to:

Satellite measurements show sea-level is rising at 3.4 millimeters per year since these
records began in 1993. This is 80% faster than the best estimate of the IPCC Third
Assessment Report for the same time period.

(see here)

Note that we have a fourth assessment report since 2007, so why wasn't that used for reference?

Does anybody happen notice that "accerelation" in the last few years?

 

[vanesch]

Could anybody reproduce that peer reviewed article that claimes two meters?

No, that its rise will have an UPPER LIMIT of at MOST 2 meters.

http://www.sciencemag.org/cgi/content/abstract/1135456

A semi-empirical relation is presented that connects global sea-level rise to global mean surface temperature. It is proposed that, for time scales relevant to anthropogenic warming, the rate of sea-level rise is roughly proportional to the magnitude of warming above the temperatures of the pre–Industrial Age. This holds to good approximation for temperature and sea-level changes during the 20th century, with a proportionality constant of 3.4 millimeters/year per °C. When applied to future warming scenarios of the Intergovernmental Panel on Climate Change, this relationship results in a projected sea-level rise in 2100 of 0.5 to 1.4 meters above the 1990 level.

This is one of the references given in the Copenhagen Climate Update Report, of which we talked about in the other thread here that justifies their claim that the rise will not be larger than 2 meters in 2100.

 

[Andre]

The article of Rahmsdorf is 2006, the "upper limit" of Siddall et al 2009 is 82 cm.

As far as I recall there was also a upper limit of a climate sensitivity of 11 or so degrees per doubling CO2 in one model run.
Maybe we can also claim that the sea level rise will not exceed 70 meters in 2100.

 

[Andre]

Anyway, it may be known that the start of the Holocene was exceptional warm, the period is known as the Holocene Thermal Optimum that lasting from about 9000 - 6000 years ago with temperatures several degrees degrees warmer than today. The warmth can be explained by an insolation maximum due to a maximum obliquity. We wondered sometimes why this period is not called the "Holocene Thermal Catastrophy", on the contrary, it's the time of the early civilisations to emerge.

Anyway, non of the ice sheets melted in that period of several thousand years and there are no indications that sea level rise (after the glacial period) accellerated abnormally as a reaction to the warmth.

References figure compiled by Robert A. Rohde

Fleming, Kevin, Paul Johnston, Dan Zwartz, Yusuke Yokoyama, Kurt Lambeck and John Chappell (1998). "Refining the eustatic sea-level curve since the Last Glacial Maximum using far- and intermediate-field sites". Earth and Planetary Science Letters 163 (1-4): 327-342. doi:10.1016/S0012-821X(98)00198-8
Fleming, Kevin Michael (2000). Glacial Rebound and Sea-level Change Constraints on the Greenland Ice Sheet. Australian National University. PhD Thesis.
Milne, Glenn A., Antony J. Long and Sophie E. Bassett (2005). "Modelling Holocene relative sea-level observations from the Caribbean and South America". Quaternary Science Reviews 24 (10-11): 1183-1202. doi:10.1016/j.quascirev.2004.10.005
Morhange, C., J. Laborel, A. Hesnard (2001). "Changes of relative sea level during the past 5000 years in the ancient harbor of Marseilles, Southern France". Palaeogeography, Palaeoclimatology, Palaeoecology 166: 319-329.

 

[hamster143]

You've been listening to too many granola heads. There are wackos on both sides of the global warming debate, and the wackos on the left care more for polar bears and the fragile environment than they do for humanity. The fragile environment is pretty dang robust. (Aside: The sheer number of humans around does a lot more harm to the environment than a few meter rise in sea level will do.)

Our modern society is not so robust. A few meters rise probably will result in significant economic damage.

Given characteristic vertical scale of Earth's terrain on the order of 10 km, a 2 m rise would decrease the amount of available land by something like 0.02% (assuming no effort to protect valuable coastal real estate from flooding).

Even coastal cities usually have the bulk of their areas at significant elevations above sea level. For example, Manhattan is one of the flattest, lowest-lying cities in the United States. 2 m rise could be enough to submerge parts of WTC site (which is almost next to the water to begin with), but the foot of the Empire State Building is 14 m above sea level, and much of the Central Park is at 20-40 m, so neither of those would be affected by any foreseeable level of sea level rise. In San Francisco, the damage would be limited to a couple of blocks closest to the coast here and there.

So, the projected rate of sea level rise is not likely to cause significant economic damage to major countries. Some people's waterfront homes will become underwater homes, some tiny Oceanic atolls will become completely submerged, but all that is hardly significant.

There's simply not enough water on Earth to cause economically significant amounts of flooding. Even if all of Antarctica's ice were to melt, that would rise the sea level by ~40 m. And we all know that it's not going to happen, short of some cataclysmic event involving a pole shift, because much of Antarctica's surface is deep-frozen, with three to five months a year of polar nights and daily summer highs below -20 °C.

 

[D H]

So, the projected rate of sea level rise is not likely to cause significant economic damage to major countries.

You are forgetting harbors and ports. The vast majority just happen to be *at* sea level.

 

[hamster143]

You are forgetting harbors and ports. The vast majority just happen to be *at* sea level.

They are not *at*, sea level, they are slightly above sea level. If they were at sea level, they'd get flooded by unusually high tides and onshore winds (not to mention tsunamis).

So, to protect against flooding, they are raised above sea level on pillars, like this:

http://upload.wikimedia.org/wikipedia/en/thumb/1/1e/NewportPier1.jpg/800px-NewportPier1.jpg

Besides, at the timescales we're talking about (50 to 100 years), most manmade harbor & port constructions (buildings, piers, etc) will need to be rebuilt at some point anyway.

 

[vanesch]

The article of Rahmsdorf is 2006, the "upper limit" of Siddall et al 2009 is 82 cm.

So if Rahmsdorf has something like 1.4 m as an upper limit from his analysis, and Siddall 0.82 m as an upper limit from their analysis, and probably others another value, then it is reasonable to say that an upper limit of worse case is 2 m, no ?

1 m would not include Rahmsdorf and so wouldn't be "worst case", no ?

Worst case as in worst case of the paper that has the highest estimates.

 

[mgb_phys]

I happened to look at some method that brings everything back into proportions, which states that the Alestch Glacier (the biggest glacier in the Alps) has enough water to barely fill the Geneva lake (89km^3).

The world's oceans are on average about 3000m deep, if they warmed up enough to expand by 0.03% that's a 1m rise in sea level.

 

[mgb_phys]

IIRC the oceans turn out to be a lucky break, because of water's odd density behavior a degree temperature change doesn't have much of an effect on the sea level.

London is in trouble from storm surges if increased temperatures lead to more violent weather, and it doesn't help that it's sinking at about the same rate as the current sea level rise. But that's their fault for building the place in a swamp.

 

[Xnn]

Here's the deal; sea levels are currently rising about 3 mm/year on average. Over a century that works out to about 30cm or 1 foot of rise; not a big deal. As global temperatures rise, the rate of sea level rise is likely to accelerate. However, based on paleodata, it's unlikely to exceed 2cm/yr.

The last time atmospheric CO2 levels were similar to today was about 3 million years ago during the Middle Pliocene. During that time, sea levels were between 20 to 30 meters higher than they are right now. However at 2cm/year, it would still take over a thousand years to realize that amount of change.

So, bottom line, the rate of rise is slow enough that human civilization can rebuild infrastructure quick enough to adopt to the change. However, over the long term there will be a significant change to the coastlines.

Here's a paper from Nature on the subject:

http://www.nature.com/ngeo/journal/v2/n7/abs/ngeo557.html

Antarctic temperature and global sea level closely coupled over the past five glacial cycles

E. J. Rohling1, K. Grant1, M. Bolshaw1, A. P. Roberts1, M. Siddall2,4, Ch. Hemleben3 & M. Kucera3

Ice cores from Antarctica record temperature and atmospheric carbon dioxide variations over the past six glacial cycles1, 2. Yet concomitant records of sea-level fluctuations—needed to reveal rates and magnitudes of ice-volume change that provide context to projections for the future3, 4, 5, 6, 7, 8, 9—remain elusive. Reconstructions indicate fast rates of sea-level rise up to 5 cm yr-1 during glacial terminations10, and 1–2 cm yr-1 during interglacials11, 12 and within the past glacial cycle13. However, little is known about the total long-term sea-level rise in equilibration to warming. Here we present a sea-level record for the past 520,000 years based on stable oxygen isotope analyses of planktonic foraminifera and bulk sediments from the Red Sea. Our record reveals a strong correlation on multi-millennial timescales between global sea level and Antarctic temperature1, which is related to global temperature6, 7. On the basis of this correlation, we estimate sea level for the Middle Pliocene epoch (3.0–3.5 Myr ago)—a period with near-modern CO2 levels—at 255 m above present, which is validated by independent sea-level data6, 14, 15, 16. Our results imply that even stabilization at today's CO2 levels may cause sea-level rise over several millennia that by far exceeds existing long-term projections3.

 

[Bill Illis]

Sea level varies from three mechanisms:

- Sea level falls when glaciers build up on land. Obvious enough.

- Sea level falls when continental land masses are concentrated together. Collisions and mountain building tend to squeeze the Earth’s landmasses together and there is less continental shelf area that can affect the average depth of the overall oceans. Related to the last reason, the ocean basins tend to be more mature and deeper in these situations. and,

- Sea level rises when new young ocean basins are opening. New ocean basins generally form at only 2,500 metres depth while mature ocean basins tend to deepen and reach a depth of about 6,000 metres after about 100 million years. That means the overall average depth of the ocean is lower when new oceans are forming. This is particularly the case during the Cretaceous when the Atlantic Ocean was just opening up

Sea level has varied between +265M 100 million years ago (when Europe, the Middle East and the middle of North America from Texas to Inuvik were flooded by shallow ocean) to about -150 metres when Pangea existed.

Haq Schutter 2008 have sea level 22 metres higher 1.5 million years ago and 100 metres higher 10 million years ago before there was significant glaciation in the northern hemisphere.

http://img687.imageshack.us/img687/328/paleosealevelcurves.png

 

[DrClapeyron]

There is a forth mechanism that has been mentioned: expansion of the ocean's lower boundary. Tectonic events and seafloor spreading likely won't make a blip of difference in sealevel change in the next 100 years of human civilization.

 

[Xnn]

A fifth mechanism involves Antarctica. The mass of ice on the continent is so large, that it exerts a gravitational pull on the nearby ocean water. This results in higher sea levels along the Antarctic coast. If the ice were to melt, then that gravitational tug would no longer be present and the sea level would tend to drop. However, that would then allow the water to flow towards the rest of the Earth thereby rising sea levels more in other regions.

There is a paper out there somewhere on this.

---
Mentors note: first find the reference, then post a reply.

Here is a reference: http://www.sciencemag.org/cgi/content/abstract/324/5929/901
"Global sea-level changes are not uniform because of regional variations in Earth’s gravity field caused by (i) ice mass change in the WAIS, (ii) deformation of solid Earth, and (iii) changes in Earth’s rotation vector as a result of mass redistribution. The combination of these effects, all self-consistently included in our solution of the sea-level equation, leads to a complex regional pattern, as already recognized in early studies [e.g., (23, 24)]."

 

[Xnn]

Sorry, but I too busy with the Holidays to spend much time looking for the paper and honestly didn't consider the claim to be all that controversial.

Anyhow, the effect amounts to about 1 meter in the extreme cases.

Here is the actual paper:
http://www.geo.oregonstate.edu/people/faculty/publications/clarkp/Mitrovica-2009-Science.pdf

 

[Andre]

The concern about the stability of the West Antarctic Ice Sheet originates from work of Reed Scherer who found young (geologically) marine diatoms under the ice sheet, which resulted in http://www.sciencemag.org/cgi/content/abstract/281/5373/82:

Scherer et al 1998, Pleistocene Collapse of the West Antarctic Ice Sheet

...The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet...

Unfortunately there is no precise dating available, which would make speculations about causality useless.

 

[Bill Illis]

There is a related issue between sea level, continental ice-sheets and marine ice-shelves: Ice-sheets build up on land; they do not build up on the ocean. Ice-shelves and land-fast ice can build up next to continents but glaciers do not occur on the ocean, only sea ice does.

There is a point where the temperatures and ocean currents are just right, and the weight of the ice sheets has isostatically depressed the continent by enough, that the ocean floods underneath and breaks-up the ice sheet. Then one just has sea ice.

This seems to have happened several times in West Antarctica and then also in the distant geologic past. North Africa was depressed and flooded early in the Ordovician/Silurian ice age (which seems to have short-circuited that ice age several different times), and then to southern South America in the Carboniferous ice ages (same short-circuit).

There might be something similar in the Arctic ocean basin in the current continental configuration. The continental shelves of North America and EuroAsia extend well into the Arctic ocean. At some point in the recent ice ages, these areas may have been isostatically depressed by ice-sheets and now that they are below sea level, no ice-sheets can build up there.

Even Hudson Bay and the Baltic Sea (which were the centre load-points of the glaciers in the last ice age) are examples of glacial isostacy leaving long-lasting impacts on the continental areas leaving them below sea level.

Mods can remove this because there is very little research literature on this issue - just something I've picked up in pieces here and there.

 

[Xnn]

Andre;

Actually, the concern with Antarctica has more to do with the topography of its bedrock.

See Figure S1 of the following link: http://www.sciencemag.org/cgi/data/323/5915/753/DC1/1

A very large portion of the ice sheet rest on land that is well below sea level with nothing between it and the open ocean. So, there isn't much to constrain it should it start to melt. Therefore, the possibility of a collapse is worthy of consideration. When state sized pieces of the ice sheet break off, they tend to float off towards warmer waters and melt much faster than they would if they stayed put.

Notice, it is a different situation than what is found in Greenland, where there is a significant amount of land surrounding most of the ice sheet. So, while we know that Greenland is melting, there isn't too much of a concern about it collapsing.

 

[Evo]

Here's the deal; sea levels are currently rising about 3 mm/year on average. Over a century that works out to about 30cm or 1 foot of rise; not a big deal. As global temperatures rise, the rate of sea level rise is likely to accelerate. However, based on paleodata, it's unlikely to exceed 2cm/yr.

The last time atmospheric CO2 levels were similar to today was about 3 million years ago during the Middle Pliocene. During that time, sea levels were between 20 to 30 meters higher than they are right now. However at 2cm/year, it would still take over a thousand years to realize that amount of change.

So, bottom line, the rate of rise is slow enough that human civilization can rebuild infrastructure quick enough to adopt to the change. However, over the long term there will be a significant change to the coastlines.

Here's a paper from Nature on the subject:

http://www.nature.com/ngeo/journal/v2/n7/abs/ngeo557.html

Good post XNN. I used to have a link to a geology site that had animations based on the known advance and retreat of past glacial and interglacial periods. If I can find the time, and it's still available, I will post it.