Research: Updated Projections of Future Sea Level Rise

An international team of climate scientists led by Anders Levermann wrote a paper than appeared in the Proceedings of the National Academy of Sciences (PNAS) of the US that described long-term (2,000y) sea level changes in response to different stabilized temperature thresholds.  You can find a short Reuters summary of the paper here.  I will provide more detail and share some observations of this paper.  The paper garnered a good amount of attention in climate activist circles since publication.

First, a little historical perspective.  Global mean sea levels rose in the 20th and 21st centuries: about 0.2m.  Prior to research conducted in the past five years, projections of additional 21st century sea-level rise ranged from another 0.2m to 2.0m.  These projections did not, in general, consider feedbacks; the parent simulations did not consider cryosphere processes (i.e., melting glaciers and the land-based Greenland and Antarctic ice sheets).  More recent research included more feedbacks and cryosphere processes, but their treatment remains immature.  Additionally, recent research started to examine projections based on realistic emissions scenarios, after researchers began to accept the fact that policymakers are unlikely to enact meaningful climate policy any time soon.  As such, sea-level projection ranges increased.  Which is where this latest paper comes in.

Levermann et al. reported a 2.3 m/°C sea-level rise projection in the next two thousand years.  Benjamin Strauss’s PNAS paper put this into context:

[W]e have already committed to a long-term future sea level >1.3 or 1.9m higher than today and are adding about 0.32 m/decade to the total:10 times the rate of observed contemporary sea-level rise

Thus, if global temperatures rise only 1°C and stabilize there (an extremely unlikely scenario), sea-levels two thousand years from now could be 2.3 m higher.  This might not sound like much, but an additional 7.5 feet of sea level rise would inundate 1.5 million U.S. peoples’ homes at high tide.  With 2°C, sea levels could rise 4.6m.  On our current emissions pathway, global mean temperatures would rise 4°C, which would result in an additional 9.2 m of sea level rise.  That’s 30 feet higher than today!  Levermann notes that these higher sea level projections are supported by sea level heights that occurred in the distant past (paleoclimate), even with their associated uncertainties.

According to Strauss’s analysis, such a rise would threaten more than 1,400 municipalities – and those are just U.S. municipalities that exist today, not tomorrow.  Globally, billions of people would be adversely affected.  What social stresses would billions of people moving inland exert?  The U.S. experienced its own small glimpse into this future post-Hurricane Katrina as a few thousand people permanently abandoned their below-sea level neighborhoods.

And now a couple of important points.  Some of the processes Levermann utilized involved linear change.  In complex systems like the Earth’s climate, very few changes are linear.  Many more are exponential.  When I discuss linear and exponential change with my students, I include a number of different examples because our species doesn’t easily understand exponential change.  We typically severely underestimate the final value of something that changes exponentially.  If changes within the climate system occur exponentially, the Levermann projections probably won’t be valid.  But their estimate will likely be an underestimate.

A USA Today article on the Levermann paper has this quote:

Looking at such a distant tomorrow “could scare people about something that might not happen for centuries,” says Jayantha Obeysekera of the South Florida Water Management District, a regional government agency. He says such long-term projections may not be helpful to U.S. planners who tend to focus on the next few decades.

Should people be scared that their communities will be underwater in 2000 years?  I don’t think they will be, number one.  Few people pay attention to trends that will affect them in 2 or 20 years.  200 or 2000 are well beyond anybody’s individual concern.  But I think society as a whole should examine this updated projection.  Do we want to condemn one-third of Florida to the bottom of the Atlantic Ocean?  Do we want to condemn thousands of towns and cities to that fate, even if the time horizon may be well beyond our lifetime?

Moving beyond the inevitable question regarding fear, what do these results mean?  We need to include results like these in planning processes.  If nothing else, planners and policymakers have more realistic estimates of likely future sea level in hand.  Those estimates will continue to change (hopefully for the better) with additional research.  But decision-making shouldn’t stop with the expectation that some future projection might be perfect because it won’t be.  The decisions we make today will have profound effects on the eventual level of the sea in the distant future.  There will also be countless effects on the climate, societies, and ecosystems until we reach that level.   That is what today’s decision-making needs to address.

Climate Central has a useful map to investigate how potential thresholds implicate sea level rise with respect to US states at different points in the future.

Ideology and Misperception in Energy and Climate

I could write a dissertation on this topic and spend the rest of my life researching and publishing on it.  I will have to settle for a short blog post for now, because my own research is in need of my attention.

People posted a number of tweets and articles on how “Political ideology affects energy-efficiency attitudes and choices“, which is the title of a new PNAS article.  The upshot: ideology trumps the free market.  This isn’t a surprise to me anymore – I’ve studied plenty of cases in the past two years that demonstrate this phenomenon.  In this case, peoples’ purchases of energy-efficient light bulbs were most influenced by what the bulb’s labeling stated.  The study made two stickers available: “Protect the Environment” or blank.  In both cases, the researchers made the same bulb benefits (energy use & cost) available to each potential purchaser.  The only difference was the presence of a blank or pro-environment sticker on the packaging.  With the pro-environmental sticker, conservatives were less likely to purchase the CFL bulb.  Without it, conservatives and liberals were equally likely to purchase the CFL bulb.  That’s not rational, which is a significant assumption of modern economic theory.  The result shows, unsurprisingly, that peoples’ behavior depends on their personal ideology and value system.  This has obvious implications for climate change activists: you have to operate in the value system of your targeted audience if you want them to receive your proposals well.  Beating the same drums harder won’t make conservatives care about climate change.

Climate groups are willfully failing elsewhere.  A new Yale Project on Climate Change Communication and George Mason University Center for Climate Change Communication poll demonstrates that increasing numbers of Americans are drawing incorrect conclusions from recent weather events to climate change.  The warmest year on record in the US (2012) was made more severe due to global warming, according to 50% of respondents.  A similar number believe the ongoing US drought is worse due to global warming.  The results go on and on.

Here is the rub: these beliefs have no basis in scientific fact.  2012 US temperatures were largely influenced by natural interannual variability.  It was warmer than 1998 by more than 1°F, which is significant.  But identifying a global warming signal in one year’s temperature data for the US is beyond the current capabilities of science.  We can say more robustly that the 2000s were significantly warmer than the 1990s, which were warmer than the 1980s, etc.  2012’s temperatures were extreme and it had implications that are still being felt by human and ecological systems.  The important point there is this: are existing systems capable of handling today’s weather extremes?  If not, we should do something.

The belief in climate change enhanced drought is also unsupported, as I wrote about a couple of weeks ago.  Initial findings from a NOAA-led team were unable to detect a global warming-related signal in either the onset, magnitude, or extent of the extraordinary 2012 drought.  This isn’t particularly surprising when you consider the last two droughts of similar extent and severity occurred in the 1950s and 1930s – prior to much anthropogenic forcing.  Specifically, they found that “The interpretation is of an event resulting largely from internal atmospheric variability having limited long lead predictability.”  Again, this drought is producing effects, but it isn’t directly attributable to climate change.  The question remains: are existing systems capable of handling these types of extreme events?  If they aren’t, we should do something about them, not draw unscientific causal linkages in an effort to build support for change.

The IPCC’s SREX report (Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation), issued just last year, reinforces this message.  There is a detectable global warming signal in a few measurable parameters such as temperature, water vapor, and sea level change.  But the climate system retains a great deal of natural variability which scientists do not fully understand.  Climate conditions will change in the next 90 years, but the likelihood of those changes varies.  Weather conditions may or may not change.  Their inherent transience makes it difficult to ascribe causal factors behind any changes.  Note further that climate projections of the 2090s are not climate conditions of the 2090s or 2010s.  Identifying likely future changes does not translate to detecting those changes today.

Yale and George Mason should digest their poll results along with the latest guidance from scientific peer-reviewed literature to help guide their communication efforts moving forward.  Given the results of this latest poll, they have their work cut out for them.  Framing, whether it is related to selling CFLs to a diverse public or differentiating between weather and climate, is critically important in climate communication.

Four-Corners Tree Die-Off Tied To Global Climate Change Drought

This post will cover a lot of ground.  I’m writing it having just read a PNAS paper from 2005 about a massive vegetation die-off event being tied to global climate change-type drought in the four-corner states.  I have been thinking that such a study should be done as I read and learned about the various pine beetle epidemics afflicting Western North America.  The paper, “Regional vegetation die-off in response to global-change-type drought”  contains the kind of information that is critical in piecing a number of different threads together to weave a coherent story.  The results contained within the paper, which can also be seen at this PNAS website,  provide a profound message about the impacts of climate change.  Such impacts have already occurred.  As I’ve written recently (here and here, for example), they are growing in number and intensity.  We ignore them at our (and the Earth’s) peril.

A series of big messages I got from this paper can be summed up as follows.  With human-forced climate change, warmer droughts are predicted to occur more often.  One such drought has already occurred (and could be continuing to occur) in the southwestern U.S.  That drought has had a profound impact on a large region’s worth of vegetation.  That impact came in two waves: the drought weakened the vegetation which then fell to the beetle epidemic.  The beetles were able to spread due to the warmth that characterized this drought.  With this and other region-wide die-offs, the potential for large changes in carbon stores is real we will face with their consequences.  As a result, carbon-related policies must be prepared to take such die-offs (and their after-effects)  into account.  The failure of region-wide ecosystems, a disaster on its own, would also present a real danger to our society.

The paper identifies regional-scale mortality of overstory trees.  Such events alter ecosystems and land surface properties for decades.  Greenhouse forcings are expected to amplify the periodic, cooler droughts found in previous climate regimes.  The drought that has occurred across the southwest since 2000 offers evidence about how those forcings manifest.  [On a short tangent, the widespread, severe drought in Australia provide additional evidence.]  This paper focused on a Piñon pine die-off.  Additional trees act as overstory species across the four states studied.  At this time, I’m not aware of similar studies detailing the greenhouse-forcing-drought-beetle-die-off relationship as it relates to those species.  It is something I will look for after writing this.

There is one figure in this paper that I want to draw particular attention to:

This figure shows annual average temperatures and precipitation values for all the stations included in the study.  The yellow-shaded vertical bands point out two regional-scale droughts – the first in the 1950s and the second in the early 2000s.  In particular, I want to draw attention to the rise in average annual temperatures from the mid-1990s to the mid-2000s (top panel): from ~10.7C to 12.3C.  Combined with the corresponding drop in precipitation from 380mm to ~250mm, this is what the authors have characterized as a global-change-type drought.  It contrasts with the 1950s drought by being statistically warmer to a significant level.  The bottom two panels also deserve some attention.  Two of the last four years in the study exhibited maximum average annual temperatures at the 90th percentile (panel c).  Three of the last four years in the study exhibited minimum average annual temperatures well above the 10th percentile (panel d).  That information isn’t available from the top panel

The reason I draw attention to the temperature rise in particular is the warning it provides about anticipated future warming across the region as the climate continues to respond to greenhouse forcing.  Under scenarios now considered likely with the “warming in the pipeline”, temperatures across this region are expected to rise another 2-10C.  As I wrote above, this paper demonstrates the impacts that warming has on dominant vegetation types: water stressing the plants and allowing bark beetle infestations to spread unabated.  With even more warming, what effects will ecosystems in the region experience?  I’ve written before about the bark beetle problem affecting the higher elevations of Colorado and other regions across the Rocky Mountains (see list below).  Those trees were impacted in a similar fashion that the Piñon trees were in this study.  How many additional species will be stressed to the point that they will also experience region-wide die-offs?  Under those same climate change scenarios, annual precipitation is expected to continue to decrease.  That decrease will be for all purposes permanent as far as humans are concerned.  Desert-level precipiation amounts are quite possible for hundreds of years.

Now look at the graph more closely.  We’ve seen the devastating effects just a small quantitative amount of warming has already had.  That’s one of the real dangers of climate change: ecosystems are quite used to the climate of the 20th century (in a larger sense, that of the past few thousand years).  There is no way of accurately foretelling how those ecosystems will respond to a significantly different climate, which we might already have entered into.  The die-offs I’ve seen and read about; the shifting climate and ecosystems zones I’ve seen evidence of tell me that the climate at the end of the 21st century could be quite different than the one of the 20th century.

Expanding on this a bit: at what stage would prairie grass die-off?  I can hear the denialist line about tree die-off and small animal die-off not being a big deal and not indicative of climate change.  The level of tree die-off discussed in this paper was unprecedented in scope: all ages, all sizes were affected.  Beyond that though, I wanted to come up with a scenario that would provide more visceral evidence of climate change impacts on human society.  If grass or hay or the like experienced a regional die-off due to an expanding, long-term warm drought, what would we do?  If cattle started dying by the millions due to water stress and epidemics, would more people take notice?  I have to think so.  I hope it doesn’t get to that level, but it might before we all aggressively look for greenhouse forcing solutions.

One additional question I have is what story does the post-2004 data tell?  I will look for additional, related studies to this one to fill out the scene.  It was somewhat surprising that this study was published in 2005 .  Nobody I’ve spoken to about the ponderosa pine die-off was aware of this paper – which is part of the reason I’m writing about it.  If anyone is aware of such a study, I’m all ears.  Otherwise, I’ll write something up on whatever I find.

Cross-posted at SquareState.
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Here is a list of some of the bark beetle epidemic posts I’ve written:

Western Forests Could Become Carbon Source, Not Sink

2008 Pine Beetle Kill: 400,000 acres in CO

Healthy Forests/Vibrant Communities Act of 2009

Wilderness Society’s Aerial Investigation of CO Pine Beetle Kill

Beetle Killed Trees May Be Allowed to Burn

Battling the Mountain Pine Beetles

Catastrophic beetle kill in Colorado