Might we see a 4.6 foot sea level rise by the end of the century?

Question

The IPCC projects that sea levels will rise by 7 to 23 inches during the 21st century, but this estimate assumes no acceleration of ice flow in Greenland or Antarctica and does not fully account for some positive feedback processes, such as the release of additional CO2 from tundra soils as the planet warms.

A new study published in Science on January 19, 2007 projects that sea levels will rise by 20 to 55 inches this century based on recent observations. This study was published after the deadline for consideration by the IPCC.

http://www.pik-potsdam.de/~stefan/Publications/Nature/rahmstorf_science_2007.pdf

"A rise of over 1 m by 2100 for strong warming scenarios cannot be ruled out...on the other hand, very low sea-level rise values as reported in the IPCC TAR now appear rather implausible in the light of the observational data."

Do you think - as several of us have been saying - that the IPCC sea level rise projections are too conservative?

casteye - read my profile for my educational background

vlad - thanks for the compliment

Answer 1

Good question. As with all predictions, no-one can say for sure just what will happen which is why maximum and minimum values are given so as to provide a range.

What we can do is to look back at how sea levels have behaved in recent history, doing this shows that there is a doubling in the rate of rise approx every 50 years.

100 years ago sea levels were rising by approx 0.7mm / 0.03 inch a year, 50 years ago they were rising by approx 1.6mm / 0.06 inch a year, today they're rising by 3.1mm / 0.12 inch a year. If this trend continues into the future, we can expect sea levels to be rising by 6mm / 0.24 inch a year come 2050 and 12mm a year by 2100 / 0.47 inch. That works out to be approx 750mm / 30 inches.

Recently there have been more detailed examinations into the effects of melting ice and thermal expansion of the oceans. The latest findings, substantiated by actual observations, is that the ice is now melting faster than was previously expected. Consequently, previous predictions should be revised upward and a sea level rise of 4.6 foot now seems more likely than previously thought.

Changing the subject slightly. Many of the IPCC predictions (along with those of other bodies) naturally tend to be on the conservative side as this is the way of scientists, to err on the side of caution. Not only is this the case with sea levels, but with the extent of the effects of climate change and with temps themselves. The most recent IPCC report (IPCC AR4 WGIII - Mitigation) will be published next month but is already available online, this shows that temps are rising faster than the previously published reports say.

Worryingly, the observed rate of global warming and climate change is showing itself to be faster than many people had previously thought. The melting of the Arctic ice last season leading to the opening of the elusive northwest passage being a classic example, that wasn't expected to happen for many years yet.

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EDIT: TO JIM

There's a reason why I focussed on short term trends and that is, quite simply, that global warming has only been with us for a short time.

If we introduce long terms trends it becomes even more apparent that sea levels are NOT following any natural pattern. Until recently the rate at which sea levels have been rising has been decreasing since the end of the last 'ice age'. Here are the figures...

4000 to 8000 years ago - rise of 0.5mm a year (avarage)
1000 to 4000 years ago - rise of 0.15mm a year (slow)
200 to 1000 years ago - rise of 0.1mm a year (very slow)

200 years ago - rising 0.1mm a year (very slow)
100 years ago - rising 0.7mm a year (average)
50 years ago - rising 1.6mm a year (rapid)
Now - rising 3.1mm a year (very rapid)

Answer 2

I think that the distribution of the melting ice is very important for this problem. If one considers only the heat capacity of ice and the heat of fusion, the time required to melt all of the ice is on the order of 8000 years. Initially, most of the extra energy just goes into warming Antarctic ice from -30 C to 0 C. On this basis, one would expect a slow rate of sea level rise at early time and a very rapid rise in the last millennium. This simple model does not include the effects of ice transport, which would tend to make the curve closer to linear. I think that the current rate of sea level rise may be a spike in the base rate from the melting of small glaciers. After the small glaciers are gone, the rate of sea level increase may decrease, at least in the short term. Do small glaciers have enough volume to sustain the current rate of sea level rise for the next 100 years?

Answer 3

Wow really?

I knew the sea would raise 20 feet if Greenland or West Antarctica melted and 4.5 feet is what not even 1/4 of the ice that is expected to melt.

That would mean a lot of displaced people in this world. And guess where there moving? To higher grounds overpopulating the rest of the world and therefore hurting the environment even more. Its so sad how all this is happening because humans can't change their ways.

Answer 4

The problem with using small times scales such as used by Trevor is that ignores long term trends and focuses on short term trends that are obviously influenced by the recent warming trend. There is no guarantee that the oceans will be 1 foot higher, 1 foot lower, or 4 feet higher. It depends on a lot of things including temperature and precipitation. Venice was built on a sinking bog and it has survived and even flourished. Cities or communities built in stupid places will have to adapt or move. Even if the ocean rose 4 feet, it wouldn't be that bad a thing. As with everything, there are trade offs both good and bad. The earth warming isn't all bad.

Answer 5

Have you heard the philosophical explanation for why we are here? Well if we weren't here we wouldn be here to ask that question.

Why do all the reports you quote have a very pesimistic outlook? Because if they didn't you wouldn't quote them.

As someone who is not a climate scientists, but knows something about science, I would say I think positive feedback for global warming mechanisms is unlikley to occur.

We have yet to see positive feedback processes at work on the earth. We can see lots of examples of negative feedback. For every ton of CO2 we emit into the atmosphere, one third goes straight into carbon sinks. For every fraction of a degree the earth warms by, the earth radiates more energy into space.

I wouldn't say that positive feedback is impossible, but where else in nature do you find a system with positive feedback - only a system in an unstable state like a forrest fire - the hotter it gets the more heat it generates. This type of system can only exist in that state briefly. The earth has been around in its present form for a long time.

Answer 6

O ben, how is that feedback? It has no effect on future C02 emissions, you are no scientist.

Yes, the US, India, and China beat the IPCC report down to less scary levels so as not to scare thier populaces.

My gut instinct is that the rising sea levels aren't going to be as important as the storms, fires, floods and droughts. Some cities will have to be abandoned, but that will be predictable and could be orderly without a massive drain on resources.

The storms etc. will be more difficult to plan and budget for and will punch bigger holes in infrastructure.

Of course this will vary depending on wether you live in Switzerland or Bangledesh. But I think the emphasis which is always placed on rising sea levels is simplistic, perhaps that's why it is deemed to be 'effective'.

Answer 7

Over the last two years I have read many news articles on the web that have phrases like, scientists stunned, scientists amazed, scientists surprised.........by the rate of melting glaciers, ice sheets, etc. They are repeatedly saying that their models were wrong and things are moving much faster than they expected. I believe we will see major cities flooded in our lifetimes. If these cities do not create emergency plans and build for the future we will be looking at an economic nightmare. I can't imagine how the economy can withstand world-wide natural disasters. Both of my employers have many branches in these cities that sit low by the sea.........

Answer 8

While I contest Dana 1981 I dont feel a need to critic his credentials Cateye. YA should be open to all irregardless of educational background Dana especially brings to this forum alot of intelligence

Answer 9

Extremely doubtful.

"Solar scientists predict that, by 2020, the sun will be starting into its weakest Schwabe solar cycle of the past two centuries, likely leading to unusually cool conditions on Earth."

Answer 10

No, we won't see anything, we'll be dead. What a stupid prediction, when the south pole is actually refreezing.

Do you really believe all the nonsense, or are you paid by some socialist politician to push this global warming myth?

I'm just asking because most educated people see through the hoax. Are you a high school grad? I understand your ignorance if you're still in high school.