One of the most important and threatening risks of climate change is sea-level rise (SLR). The mechanisms are well understood, and the direction of changes in sea-level is highly certain – it is rising and the rate of rise will accelerate. There remain plenty of uncertainties (i.e., a range of possible outcomes) about the timing and rate of rise that have to do with how fast we continue to put greenhouse gases in the atmosphere, the responses of (especially) ice sheets in Greenland and Antarctica, and the sensitivity of the climate.
Even little changes can have big consequences. As we saw with Superstorm Sandy, where extremely severe weather was combined with a very high tide, on top of sea levels that have risen six to nine inches over the past century, even a little bit of sea-level rise around the world has the potential to cause hundreds of billions of dollars of damages and the displacement of millions of people.
The Pacific Institute, among many other organizations, has been working to understand and evaluate the nature of the threat of sea-level rise and the risks posed to coastal populations, property, and ecosystems. In 1990, a colleague and I published the first detailed mapping and economic assessment of the risks of sea-level rise to the San Francisco Bay Area, looking at populations at risk, the value of property in new flood zones, and the costs of building some kinds of coastal protection (“adaptation”) to protect higher valued assets. That early report can be found here.
Then, in 2009 and 2010, the Pacific Institute, with funding from the State of California, conducted a detailed, high-resolution mapping analysis of the entire coast from Oregon to Mexico. We analyzed a set of sea-level rise scenarios developed by the Scripps Institution of Oceanography and worked with the California Energy Commission, the Metropolitan Transportation Commission, the Ocean Protection Council, the National Oceanic and Atmospheric Administration, the US Geological Survey, FEMA, and others to evaluate the risks to people, property, transportation infrastructure, ecosystems, power plants, wastewater treatment plants, and more, should those scenarios of sea-level rise happen. The full peer-reviewed report, the high resolution maps, specialty maps, and all open source GIS data can be publicly downloaded here. (A peer-reviewed journal article was also published.) That analysis suggests coastal regions are highly vulnerable to even modest sea-level rises with hundreds of thousands of people and more than a hundred billion dollars of infrastructure already in zones at risk of future flooding.
I was reminded this week, however, of the difficulty some people have in understanding the nature of climate risks, when a climate skeptic who shall remain nameless started tweeting his misunderstandings to me without having read our studies (I know this because after I pointed out his errors, he asked me to send the studies to him). My internet-savvy sons have tried for years (only partly successfully) to teach me: DNFTT. But these tweets offer insights into what might be more general misconceptions, so let me address some of them for those who actually want to help the public understand the real risks of climate change.
Misunderstanding #1: Predication versus Scenario. There is a big difference between a prediction and a scenario. Scenarios are tools for examining how changes in some kind of conditions (such as greenhouse gas concentrations) might affect something else (such as climatic conditions or sea-level). They are stories of possible futures based on a range of assumptions. Almost all studies of climate impacts evaluate scenarios to examine possible future conditions, risks, and threats. Climatologist Gavin Schmidt sometimes uses the following:
- Forecast: What you think will happen in the future (could be probabilistic), but with no conditionals. Used in weather forecasts, sales forecasts etc.
- Prediction: A much broader category of scientific statement that implies a complete specification of the circumstances under which X would be expected.
- Projection or Scenario: A conditional prediction about the future. i.e., if a certain set of circumstances come to pass, the climate will respond in the following way.
In the case of sea-level rise, climate modelers and oceanographers make projections of how sea-level would react to a range of assumptions about energy use and type, greenhouse gas emissions, and climate and ice sensitivities. These are not predictions. In the case of our reports, we evaluate the implications for coastal regions should these future sea-level rises occur. This is a risk and vulnerability assessment. In fact, for the estimates of sea-level rise in our study, we clearly note that changes could be both smaller or larger, and slower or faster than our evaluation. None of this is actually relevant to our estimate of the things currently at risk from a 1.4 meter rise.
Misunderstanding #2: Linear versus Exponential. There is sometimes confusion in some people’s minds about the difference between a linear trend and an exponential trend. In this case, data on actual changes in sea-level suggest that the recent rates of rise are between 3 and 3.5 millimeters per year. If sea-level changes are linear, then it is easy to project past trends forward: 100 years of rise would add between 0.3 and 0.35 meters. This is what my tweeter did, in an effort to say SLR is a smaller problem than the state-of-the-science 1.4-meter scenario we evaluated. Why the difference? Because climate change, and sea-level responses – are not linear; they are exponential. This means the sea level in the future will rise at an accelerating rate, leading to a much higher end point for any given year. Figure 1 shows this simple concept, but also shows that in the short term, it may be hard to distinguish between the two. A high-school student would get an F for assuming a linear rate for an exponential process. I know of no climate scientist who believes the climate will change in a linear fashion if there is continued exponential growth in greenhouse gas emissions.
Misunderstanding #3: Evaluating Average versus Extreme Risks. Climate scientists are a conservative lot (in the scientific sense, as shown in a recent journal article). As a result, assumptions and scenarios that are typically analyzed (including the ones we used, developed by the Scripps Oceanographic Institute) are in the middle of the range of what could plausibly occur. In particular, even the exponential rate that produces 1.4 meters of rise by around the end of the century includes no rapid acceleration of ice-sheet melt or ablation or other factors that could lead to even faster rates of increase or higher rises. There are some far more disturbing sea-level rise scenarios out there but we didn’t analyze them. Any criticism that the scenarios evaluated were too extreme could be equally balanced by criticism that they were not extreme enough. The most recent report on SLR scenarios for the U.S. offers a range from 0.2 meters to 2 meters by 2100 (see Figure 2).
Misunderstanding #4: Beware False Dichotomies and Ad Hominem Arguments. This skeptic opened his assault on the sea-level science discussion by arguing that I must not care about sea-level rise because my office was nearly at sea-level. First, a minute spent with Google Earth or a topo map would have shown that our offices are actually around +40 feet above mean sea-level – not in a vulnerable zone even with expected climate change over the next century (barring some more catastrophic scenario), and second, even if my office was in a vulnerable zone, it wouldn’t mean I didn’t care about the future risks of flooding. His ad hominem response was “OK I get it it [sic], the plan is to sit tight and laugh at others [sic] misfortunes.” I know, DNFTT.
Misunderstanding #5. Mitigation versus Adaptation versus Suffering: That same nasty tweet also reveals a deeper misunderstanding about the nature of responses to sea-level rise or any other climate impacts. We only have three options for sea-level rise: trying to reduce the rate of rise (mitigation), coastal defense or retreat (adaptation), and suffering the impacts. People and valuable property in zones threatened by sea-level rise will either suffer greater and greater damage, or will have to be protected with new costly infrastructure, moved away over time in advance of rising seas, or abandoned. These are issues discussed clearly in our studies. Moreover, our work at the Institute explicitly identifies vulnerable populations and strategies to protect them.
This particular climate skeptic lives nowhere near the coast. That could partly explain his lack of understanding or interest in the threats posed by sea-level rise to our extensive coastlines. But the risks facing his own community include growing heat stress and extreme temperatures, loss of inexpensive local hydropower generation, increased forest fire risks, greater air pollution, and, should sea-level rise get really bad, migration of lots of people to his community! More on these risks later.
Let’s put these errors and misunderstandings to rest and begin the necessary climate mitigation and adaptation responses, soon, or those exponential curves will begin to bite.
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Every 'skeptic' should read and try to understand this article.
(You were much too kind to your tweeter, who has never earned the courtesy from you. Quite the reverse.)
The Washington Post:
The Arctic Ocean is warming up, icebergs are growing scarcer and, in some places, the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consul Ifft, at Bergen, Norway.
Reports from fishermen, seal hunters, and explorers all point to a radical change in climate conditions and hitherto unheard-of temperatures in the Arctic zone.
Exploration expeditions report that scarcely any ice has been met as far north as 81 degrees 29 minutes. Soundings to a depth of 3,100 meters showed the gulf stream still very warm.
Great masses of ice have been replaced by moraines of earth and stones, the report continued, while at many points, well known glaciers have entirely disappeared.
Very few seals and no white fish are found in the eastern Arctic, while vast shoals of herring and smelt, which have never before ventured so far north, are being encountered in the old seal fishing grounds.
Within a few years, it is predicted that, due to the ice melt, the sea will rise and make most coastal cities uninhabitable.
November 2, 1922,
More logical fallacy. Even if this is a real story from 1922 (please provide a link), the fact that it might have been wrong then says NOTHING about whether the climate is changing and sea levels rising now. Science is testable. That's its beauty.
"a climate skeptic who shall remain nameless"
That would be the owner of a blog known by the acronym WUWT, yes?
So let me see if I've got this clear. We should be worried because a) sea levels might be rising; b) if they're rising that rise might not be linear; c) if they're rising and that rise is not linear, it might be exponential; d) if they're rising and that rise is exponential, it might go on for a long time; e) if they're rising and that rise is exponential and it goes on for a long time, it might cause some damage. Is that right?
Let me point out that by that reasoning we could expect our seawater to soon flood the moon, and a week or so later to put out the sun. Within a year or so the entire universe will be full of nothing but seawater.
And if you can see the flaws in that argument, then Peter Gleick's shouldn't be too hard to refute.
What a silly comment but worth posting. Readers want to weigh in on the strawman argument here? ? Just because an exponential curve can't go on forever doesn't mean it isn't exponential....]
"I know of no climate scientist who believes the climate will change in a linear fashion if there is continued exponential growth in greenhouse gas emissions."
Do you know of any climate scientists who believe the climate will change in a linear fashion if there ISN'T an exponential growth in greenhouse gas emissions?
As a limiting case all the polar ice will melt and the curve will flatten out. Or we'll extract and burn as much carbon as we can readily obtain and CO2 levels will stabilize or even start to decline. In either case the sea levels will be a lot higher than they are today.
I think it would be useful if our host discussed just why the curve is, at present and likely for some considerable time to come, best modeled as an exponential.
A silly comment indeed. @Jon, do you agree that sea levels are currently rising? If so, what could be feeding this process? Think about it. There are billions upon billions of tons of fresh water locked up in the ice sheets of Greenland, Alaska and Antarctica. (Please note, I do not include sea ice, which will not contribute to SLR.) If it is true that greenhouse emissions are causing the planet to heat up, and if this is melting aforementioned ice sheets, this WILL have an effect on our sea levels. Because leading climatologists have predicted this rise in sea levels to be exponential does NOT mean the levels will rise indefinitely (to the nonsensical levels as suggested in your post). Rather, sea levels will rise as long as there is landlocked ice to melt, and see its meltwater run into the oceans. This, we are told, will probably take thousands of years. But the more immediate effect of SLR (possibly within the next 50-100 years) may be the inundation of coastal cities around the world. I'm guessing that's not a problem to you?
So, that's the explanation for the sea-level rise scares, it's exponential. It hasn't happened yet, but it will. And Figure 2 says it could even be worse than shown in the figure. Except, by eyeballing the chart the extreme and intermediate curves are eliminated.
So, how much ice has to melt to get this sea level rise? What ice is melting at that rate? And where are the data showing the ice loss corresponding to the rate of rise?
All those data are easily available for anyone who knows how to search the internet. I prefer google.
Linear growth is a growth in absolute numbers (y = a + b*t), whereas exponential growth is a growth in percent (y = a^(b*t)). For example, a constant 0.2 mm/year growth would be linear, whereas a constant 1% growth would be exponential.
Ecological growth with unlimited boundaries is often exponential, and our flawed economic system attempts to be exponential: economic growth should be a percentage of the current economy size. If GHG emissions are proportional to the size of the economy (as the work by Timothy Garrett, University of Utah, suggests), then growth in GHG emissions may be exponential.
There is no doubt that sea level rise is very dangerous and that the rate of sea level rise is increasing with rising temperatures. But how can it be exponential? If the rate of SLR is expressed in % rather than absolute numbers, what is the base, what is the overall quantity that this % relates to?
The word "exponential growth" is unfortunately quite often mis-used. No doubt that the rate of growth is increasing, but I'm pretty sure the correct model is *neither* linear *nor* exponential...
Hmm, not sure where your confusion comes from: When the rate of something changes in an accelerating way as noted in your exponential growth equation, and as shown in the curve (Figure 1) in my post, it is exponential.
Unfortunately we have to accept that some people will never allow themselves to figure out a) why understanding our world is important or b) why projections are important and very useful tools to aid decision-making.
I'm not sure that Jon's argument is a strawman. It makes no sense to me at all. He seems to be making a giant leap from sea levels rising from known causes on earth to postulating that there are oceans on the moon. Total nonsense. (Maybe he's got some notion that there is an endless supply of H2O on earth and no natural limit to the volume of the ocean.)
We've a cognitive scientist here in Australia (Stephan Lewandowsky) who might be able to explain Jon's thought processes (eg in terms of mental models).
As far as I can see, Jon's argument is indeed a straw man argument, insofar as he adds uncertainty qualifiers (all those 'ifs' and 'mights') where they don't belong and insinuates that Peter or the Pacific Institute are claiming infinite reserves of water on Earth.
Anyway, let me fix Jon's statement for him:
(By the way, in case this comes out badly-formatted, a 'Preview' button for comments would be a wonderful idea if it can be implemented.)
I don't think Jon's post qualifies as an argument to anyone - although Jon himself might think it is an argument. It seems to be simply a string of silly statements joined with punctuation - which is what I'm guessing he views Peter's post to be.
On the "Mitigation versus Adaptation versus Suffering" bit: it would be interesting to see an analysis of the ways different portions of the population choose among these options.
Jon should be embarrassed to have used his real name instead of a pseudonym.
Jon, you swung and missed the pitch at "a." This isn't "sea level might be rising." Sea levels are rising. The question that scientists are trying to answer is, how fast. Is sea level rise going to merely be bad, or is it going to much worse?
Hmm, Well Mr. Gleick makes several appeals to authority on this page, which is always interesting in this argument. But anyway, I see these projections but dont see the reasoning, where is the water coming from? Andy why should it increase so dramatically? To get the water from Antarctica or Greenland, the ambient temperature must not only increase, but increase to well above freezing long enough for the ice to melt. It would be interesting to know what the projections said in 1980, 1990, 2000, and 2010, and how they did for 2013 from those time frames. This would tell us how skillful those projections are actually likely to be.
The chairman of the IPCC has confirmed the findings of the Met office. There has been no warming for 17 years. How can we blame anything on warming that has not occurred?
James Hansen, NASAs famous astrophysicist, said in the late 1980s that if CO2 levels continued to rise under his business as usual scenario, we would see the global warming signature rise out of the statistical noise by the 1990s. Obviously, it didn't happen. Also, CO2 levels have risen much more sharply then Hansen anticipated.
If it is hot or cold, floods or droughts, hurricanes or blizzards or anything else related to weather it is global warming! A theory which cannot be falsified! How convenient and unscientific!
Empirical data in peer reviewed papers show that there is no rate of increase in sea level rise, no increase in tornadoes, hurricanes or drought.
The theory is falsified and its adherents are religious followers, not objective thinkers.
I approved this comment because the author used his real name (thank you) and because it is a classic example of non-scientific responses and misrepresentation, and hence illustrative. Both the MET office and Dr. Pachuri have been very clear about the misuse of the claim there has been "no warming for [15, 16, 17, make up your own number] years" and what the science /really/ says about temperature variability. Go see the actual MET office response. Here is an excellent link that summarizes (and provides direct links) to the details and facts here. http://www.skepticalscience.com/resolving-met-office-confusion.html. In the future, I will not permit comments that abuse science like this or liken scientists to "religious followers."
Why did the BOM in Australia recently locate their headquarters in a building whose ground floor is @2 meters above sea-level?
And why produce a report whose 'findings' contain "...the sea level in the future will rise at an accelerating rate..." yet fails to explain why this is not already apparent, given the increase in CO2 over the last 50 years of the 20th century and the level of global warming over the same period?
Nice article. However, I think the overarching problem is not treating the science as theory, but as fact. "Sea levels are rising..." is definitive, and invites argument, whereas "Data indicate sea levels are rising" is literally correct, and cannot be refused, even if the theory turns out to be wrong.
I expect we will refine climate models, further, and thus, the theory will either get stronger or be changed.
I am somewhat skeptical of the field, because of the definitive nature of the comments I see by scientists in non-refereed press. It has an air of "why can't you idiots read what I wrote".
I think another blog post by you that extends your discussion to one that explains statistical significance might be very helpful.
I'd respond to the inanity of Jon's post, but fortunately several others have already done so.
Dr. Gleick, this was an easily-digestible, informative post. I think the distinctions illuminated in "misunderstandings" #1 and #5 are most useful to the skeptic's skeptic (someone who chooses to believe that everyone's bias clouds their observations, and thus all interpretations on climate change are worthy of skepticism at the outset).
I believe that many skeptics and denialists alike (hush, Firefox, "denialist" is so a word in this context) are turned off by what is reported as alarmist propaganda. I don't believe that's the goal behind scientific scenario-building, but it is often portrayed that way in the media. It must be difficult to see academic work reduced to paranoid-tinged sound bites used to hook in a reality TV-obsessed populace.
I also concur that Jon's argument is not a strawman, unless the strawman-in-question was intended to distract you with a series of illogical and rhetorical statements. :)
"As we saw with Superstorm Sandy, where extremely severe weather was combined with a very high tide, ..."
Tangentially to your discussion I wonder if I might take exception to the sentence fragment I quote from the start of your post. I have, since Sandy struck, found myself squirming when I hear the storm referred to as a Super Storm. It caused a strong, but not super strong storm surge that devastated communities that have dodged some storms in the recent past, both autumn tropical storms and winter mid latitude cyclones, and suffered severe damage from others. The tidal multiplier was in fact modest compared to what might have occurred had the storm struck on a new instead of a full moon. Mean high water was approximately 5.3 ft under the full moon when the storm struck. Had Sandy struck on the 10/15/12 new moon, mean high water was predicted to rise to just over 6 ft. A significant difference when considering storm surge and a difference that would force us to refer to the storm as what? Super Super Duper? Putting Sandy into perspective, considering its actual strength, its track and the subsequent damage is critical, but overstating size and strength of the storm by referring to it over and over as Super Storm Sandy leaves the public believing this is as bad as it might get. That would be a mistake.
All good points... I adopted the commonly heard "Superstorm" but your observation that it could have been worse are right. Part of the problem is that it wasn't exactly a "hurricane" when it hit land (winds had dropped to just under official hurricane status), but it was obviously far, far more serious than just a "storm." So I guess people are looking for a more descriptive way to label it... "Really, really bad storm Sandy"? !
How do you know conditions allowing ice melt in Antartica & Greenland are not occurring?
Unfortunately, they are: see for example here or here, for example (references to the peer-reviewed literature are copiously provided in the links).
The 17 years of stalled warming can be found in this article (among others):
It says: "THE UN's climate change chief, Rajendra Pachauri, has acknowledged a 17-year pause in global temperature rises"
Your own link does not refute this - it mostly deals with forecasts. Forecasts and observations are very different, scientifically speaking, wouldn't you agree?
Forecasts and observations ARE different. Of course. But the continued insistence (false by the way) that warming has stopped is another misunderstanding and misrepresentation of the actual observations. Pachauri is being misquoted and taken out of context, and as one commenter has already observed, most warming is occurring as heat is transferred into the oceans. The link provided to the Skeptical Science discussion on this issue is an excellent one. http://www.skepticalscience.com/news.php?n=1889
with your statement you have ventured onto very thin ice, since even in the article you refer to (and which is hidden behind a paywall) there is no direct quote of Pachauri that comes anywhere near the claim in the headline, which would be inaccurate anyway.
Global Warming HAS NOT stopped, not even paused, it continues unabatedly.
If you want to get a little better informed about the subject, I can recommend the following webpage to you:
which directly deals with (and refutes) your claim. Actually 93.4% of Global Warming occur ion the oceans whereas the share of the atmosphere is a measly 2.3%.
Peter, no need to post this or respond, but I wanted to thank you for your continued work to educate and push back against ignorance. Your patience with many of these posters is incredible! I teach environmental
Science at the college level, and I am feeling your pain on a daily basis. I will say the younger they are they get it!
Gleick: Thanks for responding and thanks for the link.
Vennecke: Thanks for the link, but I think you misunderstand my intention here. I wasn't making any claims, except maybe the one about forecasts and observations being different. The forecasts made via computer modeling have largely overestimated the effect of CO2, projecting more warming than has actually taken place. This suggests that we have a ways to go in that area before it makes sense to trust these forecasts.
Thanks for your response to my comments regarding the use of the moniker Super Storm. i'd suggest scientists avoid using and spreading such catchy adjectives. Sandy was a devastating storm.
So I took at look at some of the seminal papers on the subject. There is not a lot of data. When it comes to climate change, I read that it takes hundreds or thousands of years to yeild statistically significant data. What I read was that year to year and intra-century data can be highly variable, or indicate correlations that do not exist. Is there sufficient data to remove all doubt on the subject? Specifically, are we sure human carbon dioxide production is causing climate change?
An excelent post. Well done Peter.
Wyong council has taken it upon themselves to say they do not believe in SLR and therefore will not include it in the Local Environmental Plan that will be in place for many years. Where does this leace the 4000 land owners that are vulnerable in the area (with many more in Gosford and Lake MacQuarie).
Misguided fools like your tweeter are only succeding in delaying the adaptive measures we need to implement now - such as preventing more investment of the communities capital in vulnerable areas.
Of course, it gets down to politics where the fossil fuel industry has become a major influence on policy due to its ability to fund disenters. This is realy a very critical issue now because decisions being made now will be driving the warming of the next 50 years and more.
We already have to deal with the changes happening and those inevitable in the next few decades. We are now dealing with the decisions that will create deeper impacts for our children and grand-children.
It is political and the coming election is likely to see the dasmantling of all our efforts so far - as typified by the recent change of NSW Govt where tey have now removed the benchmark values of 0.4m by 2050 and 0.9m by 2100.
I'm just a novice on thisl, but didn't I read somewhere that in addition to ice melt, warming sea water expands also contributing to sea level rise?
Yes, indeed. Thermal expansion accounts for some of the sea level rise; ice melt accounts for some. And there are some other far more minor factors too. Unsustainable withdrawal of groundwater adds to ocean volume. Storage of water behind reservoirs /decreases/ sea level. Irrigation that, on net, increases soil moisture, decreases sea level... all of these last are tiny, but real.
When talking about the perils of sea level rise, you and other CAGW proponents [ except for a few] never mention the factor that has been found to be the cause up to 50% of the Arctic melt, and much of the melting of glaciers and of the permafrost—ie black carbon.
Black carbon is soot, as you know---nothing to do with CO2-----and is one of many products of incomplete burning (combustion), mainly of biomass, but also , in developed countries, of diesel fuel.
Industry in developed countries produces very little, as it has to follow environment pollution laws that limit if not preclude the production of soot---so industry and coal plants in the developed countries are not the main problem with BC.
The main contributor in the developed countries is diesel fuels and forest fires, but on a global scale the big contributor to the black carbon problem and the Arctic melt and that of glaciers and permafrost, is the cooking and heating practices in use in Asian countries and the deliberate burning of the rainforests in Asia [ Asian brown cloud] and Brazil.
Black carbon emissions from China doubled from 2000 to 2006, and have increased even more since.
Many scientists, including Dr Drew Shindell of NASA and Jacobsen of Stanford , and Ramanthan and others have been warning of the black carbon effect and the catastrophic feedback cycle that follows it , for years---- at least from 2009 in relation to the Arctic ice problem----- and they testified before Congress extensively in 2010.
[ 'Washington, D.C., April 2, 2009 – An article published this week in Nature Geoscience shows that black carbon is responsible for 50%, or almost 1 ˚C of the total 1.9 ˚C increased Arctic warming from 1890 to 2007. The paper by Drew Shindell of the NASA Goddard Institute for Space (GISS) and Greg Faluvegi of Columbia University also notes that most of the Arctic warming – 1.48 ˚C of the 1.9 ˚C – occurred from 1976 to 2007. ' ]
The study 'concludes that the Arctic responds strongly to black carbon emissions from the Northern Hemisphere mid-latitudes, where the emissions and the forcing are greatest.'
[ 'Because black carbon only remains in the atmosphere for several days to weeks, reducing it can bring about almost immediate mitigation of warming, whereas decreases in temperature lag reductions in CO2 by 1,000 years or more.' ]
Considering that the rest of the earth is very much impacted by that catastrophic feedback cycle that follows the loss of albedo in the Arctic due to black carbon, and also by the melting of the glaciers and the permafrost----- why is it that almost no warmists except those scientists researching it ever even mention black carbon, let alone help with agitating for its mitigation??
It's almost as if they don't want that early mitigation to prevent the feedback cycle.
I agree with your observations about the importance of black carbon and the need for, and value of, early mitigation. But scientists DO understand and talk about this too. Thank you for adding the point to the discussion!