Does Mitigation Do Much for Sea Level Rise in the 21st Century?
April 14th, 2009Posted by: Roger Pielke, Jr.
A new paper by a group of distinguished climate scientists asks, “How much climate change can be avoided by mitigation?” This is of course an interesting and valuable question that too rarely is addressed. The paper suggests that mitigation can do very little to arrest sea level rise to 2100, here is the paper’s discussion of sea level rise:
The sea level rise from thermal expansion of the ocean (note that adding glacier and ice sheet melt could more than double this number [IPCC, 2007]) is 22 cm in the nonmitigation scenario and 14 cm in the mitigation case. Thus, about 8 cm of the sea level rise that would otherwise occur without mitigation would be averted (Fig. 1d). However, by the end of the century the sea level rise continues to increase and does not stabilize in both scenarios due to climate change commitment involving the thermal inertia of the oceans [Meehl et al., 2005]. Recent studies indicate some acceleration of glacier melt over Greenland [e.g. Joughlin et al., 2008]. Increased ice sheet calving could lead to a more rapid sea level rise that would continue for several centuries after greenhouse gas concentrations are stabilized irrespective of the emission scenario.
Thus, according to this model, with aggressive mitigation sea level rise would be slowed by about 3.5 inches by 2100 (or maybe double this amount), but would continue in either scenario (mitigation versus business as usual). Thus, for the 21st century sea level rise is an adaptation issue, not a mitigation issue. The benefits of mitigation for sea level rise, according to this paper, stretch far out past 2100, which really limits its significance in the assessment of 21st century costs and benefits of mitigation.
The paper says more, which I will follow up on, but the implication of mitigation for sea level rise seems worth highlighting.
April 14th, 2009 at 11:02 am
Given that sea levels were 4-6 metres higher than today 125,000 years ago in the last interglacial, the Eemian, which was 1-2 degrees warmer than today as well, I don’t see how a sea level rise of about the same magnitude can be avoided by anything we do. Sea level increases are part of the interglacial cycle; at the worst, human activity might accelerate this natural process by a percentage point or two.
And, as the data on previous interglacials shows, once the warmth and sea levels have reached their peak, we will move into a glacial period that last four or five times as long as the warm time. Warmer is always better than colder, even if it means higher oceans.
Even King Canute, a thousand years ago, knew that humans can’t stop the seas from rising and falling as nature wills. All we can do is cope, as we will.
April 14th, 2009 at 11:19 am
That study is founded on the flawed hypothesis of AGW caused by CO2 emissions. The mitigation calculated in the study is based on crashing the US economy and keeping millions of people in India without electricity. Those two flaws alone are enough to trash the study without checking their math.
Add the fact that sea levels have risen about 300 feet in the last 20,000 years; a few more inches doesn’t seem worth stopping the growth of the world’s economy.
April 14th, 2009 at 11:51 am
Roger,
This was exactly the message I took home from Solomon et al. recent PNAS article (http://www.pnas.org/content/106/6/1704.full). There is very little that can be done (i.e. altering our emissions pathways) to make a sizeable dent in the magnitude of sea level rise that is to come—whatever that amount may be.
-Chip
April 14th, 2009 at 1:50 pm
When laypeople are far more concerned about adherence to the scientific method than the scientists the world gets “studies” like these. Maybe the science might improve if these folks got more concerned about insuring quality control, transparency and replication instead of making grand predictions for the next century based on politicized garbage and incompetent shams.
April 14th, 2009 at 8:36 pm
We need a reality check. The Earth has not seen any warming for more than a decade. That means that CO2 as a driver of change is not a strong thesis and that we have more important things to worry about than sea levels in 100 years.
April 15th, 2009 at 9:53 am
“Thus, for the 21st century sea level rise is an adaptation issue, not a mitigation issue.”
You’re ignoring another possibility…preventing sea level rise, even while allowing emissions to proceed with “business as usual.”
“Even King Canute, a thousand years ago, knew that humans can’t stop the seas from rising and falling as nature wills.”
King Canute probably would have had a different opinion, if he’d died in 2035, instead of 1035.
I haven’t looked at the issue in tremendous detail, but based on a brief review, I think current technology and levels of wealth are sufficient to seriously consider the possibility of significantly reducing (by 50% or more) the rates of melting of the Greenland and Antarctic ice sheets.
Details to follow. (Lunch is almost over!)
…or…:-(
April 16th, 2009 at 6:22 am
Roger,
Your take on this paper seems to be different than the authors’. The title of the press release that you link to sais: “Cuts in Greenhouse Gas Emissions Would Save Arctic Ice, Reduce Sea Level Rise” The lead author is quoted as saying: “This study provides some hope that we can avoid the worst impacts of climate change–if society can cut emissions substantially over the next several decades and continue major cuts through the century.”
One of their key results (last bullet point) is that as a result of strong mitigation “The climate system would stabilize by about 2100, instead of continuing to warm.” It’s unfortunate that they exclude the potentially most important (yet most uncertain) contributions to sea level rise (from melting of ice sheets), since these potentially have the biggest impact, especially in the longer term (multiple centuries). If through our future actions we commit the world to a sea level rise that could eventually be measured in meters rather than centimeters (cf. the Emian period as the first commenter pointed out), than to me that’s something worth trying to avoid. (I live in Holland, not Colorado)
Adaptation to sea level rise without mitigation is like mopping the floor while the tap is running. First order of business is to close the tap, than you start mopping.
Bart
April 16th, 2009 at 2:52 pm
Bart- My comments are indeed different than those found in the press release. Interesting, huh?
Rather tha prioritize mitigation over adaptation, I suggest that we focus on both at the same time. They address very different timescales, as you suggest, so why present them as trade offs as you have?
April 17th, 2009 at 8:32 am
“so why present them as trade offs as you have?”
Probably because so many posters on this blog deny that humans have anything to mitigate. I think that Roger is right that we need to do both, and not try to make mitigation and adaptation fight with each other. Even if we can implement the strongest possible mitigation plans, there will be a lot to adapt to. But in order to do that, we have to move beyond the argument over whether there is anything to mitigate.
April 18th, 2009 at 12:40 pm
Roger,
You write “Thus, for the 21st century sea level rise is an adaptation issue, not a mitigation issue.” That sounds like a very strong prioritization if you ask me. I agree that both are needed; that’s just not the message that I got from your post.
Because of the large inertia involved, mitigation should take the front seat though, as per my mopping analogy (where mopping is still needed as well of course). Arguably, we still have time to adapt, but mitigation should be a long term, continuous effort in order to keep the risks manageable (which we’ll still have to do; I’m not “anti-adaptation” by any means. Dean made a good point).
Mitigation is especially important with an issue like sea level rise, where adaptation to a SLR of a few tens of centimeters can probably be dealt with by most (though not all) countries, but where the absence of mitigation runs a high risk of an eventual SLR in excess of a metre, to which adaptation starts to be a lost battle for many densely populated coastal areas.
Bart