The Great Flood(s) - Real Possibilities of Sea Level Rise?

When dealing with the issue of sea-level rise, why not start with the story of Noah's Ark. Whether a believer or not, as science and theology now both claim to provide a potential answer.

Of course we all know the biblical tale of Noah's Ark, God's condemnation and punishment on his flawed people came by the means of a great flood. Noah received a message from God telling him to build a great Ark in order to save a select few people and all the animals in their gender pairs so being able to start life afresh once the waters subsided.

Now scientific discovery has provided an alternative for the tale, as in 1999 a survey of the Black Sea continental shelf off the north central Turkish seaport of Sinop using sonar, remotely operated vehicles, and a series of dredge lowerings located, inspected and sampled an exposed paleoshoreline (past shoreline) at a depth of 155 m. In these depths Ballard et.al discovered evidence of a people who perished in a great flood of the Black Sea. Radiocarbon dating of mollusk shells collected from this ancient beach revealed that the marine flooding of the Black Sea took place between 7460 and 6820 years before present, changing it from a lacustrine (lake) to marine (sea) environment. Evidence for the people there comes ancient mud and wooden house had collapsed, and they found tools of highly polished stone, together with fragments of ceramics.

The geological evidence suggests the rising Mediterranean sea pushed a channel through what is now the Bosphorus, also known as the Istanbul Straits, and then seawater poured in at about 200 times the volume of Niagara Falls. The Black Sea would have widened at the rate of a mile a day, submerging the original shoreline under hundreds of feet of salty water. In total nearly 100,000 square miles were inundated. 

Ballard does not claim to have found the landscape of Noah but what he does know is that there has been a major flood and that people were living here when it happened. The jump to Noah comes from the timeframe and location leading some to believe this to be the source of the biblical tale, e.g. Noah's Ark came to rest in Turkey.

Regional map of the Black Sea and the surrounding landmass, including the location of mountainous terrain and locator map. The 155 m contour is shown as well as the 1999 study area (Ballard et. al. 2000).

So now onto modern day and again to use the classic symbol with flooding today, one has to look at Bangladesh.  Bangladesh is very prone to flooding due to its location at the confluence of the Ganges, Brahmaputra and Meghna (GBM) rivers and because of the hydro-meteorological and topographical characteristics of the basins in which it is situated, i.e 60% of the sea level is 6m below or more below sea level (USAID, 1988)! On average, annual floods inundate 20.5 per cent area of the country and this can reach as high as about 70 per cent during an extreme flood event. The societal exposure to such risks is further enhanced by Bangladesh’s very high population and population density. These floods cause serious damage to the economy of Bangladesh, a country with a low per capita income. Global warming caused by the enhanced greenhouse effect is likely to have significant effects on the hydrology and water resources of the GBM basins and might ultimately lead to more serious floods in Bangladesh (Mirza, 2002).

References

Ballard, R.D., Coleman, D.F. and Rosenburg, G. (2000) Further evidence of abrupt Holocene drowning of the Black Sea shelf. Marine Geology, Volume 173, Issues 1–4, 15 March 2001, Page 143.

Mirza, M.M.Q (2002) Global warming and changes in the probability of occurrence of floods in Bangladesh and implications. Global Environmental Change, volume 12, issue 2, pages 127-138.

USAID, 1988. OFDA Annual Report. Office of the US Disaster Assistance Agency for International Development, Washington DC, pp. 110–122.

A view from the past

The exciting news grabbing part of climate research is about predicting future change. As it will be extremely useful to know about future changes prior to their arrival. However as Luke Skinner successfully  argues (2008), our approach to climate change is firmly, if not completely, linked to our
understanding of the past.

This is mainly due to the role played by palaeoclimate reconstructions in shaping our expectations of the climate system, in particular via their ability to test the accuracy of our climate models. Just remember that climate is long-term conditions, whether everyday weather conditions, so don't be put off by the inaccurate weather reports you listen to!

So with this is mind let us look to the past

References

Skinner, L. (2008) Facing Future Climate Change: Is the Past Relevant?Phil. Trans. R. Soc. A 2008 366, doi: 10.1098/rsta.2008.0228.

Eat while you can

Crop yields in the United States — the world's largest exporter of agricultural products — could fall as much as 82 per cent by 2100 if temperatures rise sharply, according to a new study.

Wolfram Schlenker and Michael Roberts, American researchers, studied the impact of varying growing-season temperatures on corn, cotton and soybean yields in the US. They used agricultural records and detailed weather data collected between 1950 and 2005. 

They found a nonlinear relationship between temperature and productivity: yields increased modestly until a threshold temperature was reached at 29 °C for corn, 32 °C for cotton and 30 °C for soybean. Past these stated temperatures  the yield dropped off sharply. This was true for all regions of the US, including the warmer southern states. 

On average there are 57 days in a year that exceed 29°C. Schlenker and Roberts moddelled for future climite change finding that the number of days exceeding 29 °C in a growing season could rise to 413 by the end of the century if we do not cut our greenhouse emissions. This is of course the worst case scenario, but were it to happen maize yields would fall by 82 per cent! Even if we reduce emissions by 50 per cent by 2050, relative to 1991 levels - a target which governments are struggling to agree on and optimistic by the looks of it - yields could still fall by between 30 and 46 per cent.

The silver lining for all us that want to avoid food shortages and the inevitable price hikes is that potential gains in productivity due to raised CO₂ concentrations were not taken into account, this rise will likely partially offset any decline in yield due to warming.

Reference

Schlenker, W. and Roberts, M.J. (2009) Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change. Proceedings of the National Academy of Sciences, 106(37): 15594-15598

Policy relevant....

So here is a map of potential policy-relevant tipping elements in the climate system. It's been updated from Schellnhuber and Held (2002) and overlain on global population density (Lenton et. al., 2007). Subsystems indicated could exhibit threshold-type behaviour in response to anthropogenic climate forcing.These could be triggered this century and would undergo a qualitative change within this millennium, i.e. something man would defiantly notice!  

Exclude from the map systems are any thresholds which appear inaccessible this century (e.g., East Antarctic Ice Sheet) or the qualitative change would appear beyond this millennium (e.g., marine methane hydrates). 

A question mark indicates systems whose status as tipping elements is particularly uncertain.

I like to think that all these issues are being seriously considered by the higher ups and debated, especially at this year's climate summit. Here's hoping....

References

1. 1. Lenton, T.M. Held, H. Kriegler, E. Hall, J.W. Lucht, W. Rahmstorf, S. Schellnhuber, H.J. (2008)
      Tipping elements in the Earth’s climate system. Proc. Natl Acad. Sci. USA 105, 1786–1793.
   
   
   Schellnhuber, H-J. , 
2. Held, H. 

(2002) in Managing the Earth: The Eleventh Linacre Lectures, edsBriden J , Downing T (Oxford Univ Press, Oxford), pp 5–34.

Reversible Retreat or Unstoppable Loss?

The future of ice sheets & sea ice could be quite dramatic

The ice-albedo feedback is notorious positive feedback loop (think back to my ‘Back to Basics’ entry about feedback loops). I’m sure you’re all somewhat familiar with the concepts involved here given frequent mass media coverage. If a certain ice cover is decreasing in size, the albedo (i.e., reflectivity) of the formerly ice-covered region usually decreases. Think about how much hotter black painted surfaces are than white in mid-summer. Hence, more sunlight can be absorbed, the additional heating of which gives rise to further shrinkage. Once these ice masses have shrunk below an anticipated critical extent the ice-albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. This differing levels of albedo and extent to which they apply are ultimately linked to global average temperatures, with a positive correlation existing between reduced ice extent and increased temperatures.

The existence of this tipping point is a widely held scientific consensus. However, if we were heading into a period of glaciation and not warming (an interglacial) then the opposite would of course apply as the ice extent spread further, promoting a cooling global temperature.

Dirk Notz and Joachim Schellnhuber, in an article (2009) entitled ‘The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss’, debates (accepting the probable existence of the above tipping point) using conceptual arguments whether Artic sea ice, in a cooler climate, could recover rapidly from the loss it has experienced in recent years. The alternative being that it could not and would thus surpass the critical ice extent threshold. The author calculates this through the use of a ‘simple’ energy-balance model.

You can check it out here  if you’re at UCL (if not use the full reference at the bottom): http://www.jstor.org.libproxy.ucl.ac.uk/stable/pdfplus/40536041.pdf?acceptTC=true&acceptTC=true&jpdConfirm=true

The fundamental issue contained is whether the existence of the ice-albedo feedback does or does not necessarily lead to instability of the Earth's ice masses (a requirement for the positive feedback loop to take hold).

In addition a key distinction exists between seas ice and ice sheets, as well as the location of the ice concerned as Notz compares Arctic summer sea ice to the Greenland ice sheet and the West Antarctic ice sheet.

Ditz and Schellnhuber say that sea ice is probably capable of recovering rapidly once the climate turns cold again as there are some other feedbacks (which counter the albedo one discussed) which act to stabilise the ice, revealed in a more-complex study (Eisenman and Wettlauf, 2009).  Thus any measures taken to slow down climate warming can immediately slow down future sea-ice loss. Good News! For Arctic sea ice, he explains why the recently observed rapid decrease in ice extent, which the papers have focused on largely because of the polar bears, might just be a consequence of a smooth and slow shift in ice-thickness distribution. However if no measures were taken to combat or at least mitigate global warming then a transition to a seasonal ice-free Arctic ocean seems unavoidable, with possibly far-reaching consequences for the indigenous population, the Arctic ecosystem, and the climate system as a whole. Less good!

Where ice sheets are concerned there are no feedbacks to counter the albedo effect thus a tipping point is actually more likely, so meaning the melting would be unstoppable past a certain degree of warming, coming sooner than is the case with sea ice.

So there we have it, certainly not as straight forward as the media would have you believe (as always?), also interestingly in a sense ought not to be overly relevant to policy makers discussed previously in my blog posts, given the global nature of the forcings and impacts. However it’s all certainly relevant & I guess that means Captain Marvel and Superman are still going at it....  

Unless you were to believe Lindsay and Zhang (2005) instead who state that we defiantly have a already passed the tipping point, Captain Marvel?
 

 References 

Eisenman, I. Wettlaufer, J.S. (2009) Nonlinear threshold behaviour during the loss of Arctic sea ice. Proc Natl Acad Sei USA 106:28-32.

Lindsay, R. W., J. Zhang, 2005: The Thinning of Arctic Sea Ice, 1988–2003: Have We Passed a Tipping Point?. J. Climate, 18, 4879–4894.

Notz, D. and Schellnhuber, H.J. (2009) The Future of Ice Sheets and Sea Ice: Between Reversible Retreat and Unstoppable Loss. Proceedings of the National Academy of Sciences of the United States of America , Vol. 106, No. 49, pp. 20590-20595