Category Archives: Vulnerability

Disproportionality in Social Ecological Systems

Malcolm Gladwell has a good article on disproportionality in the New Yorker Millon Dollar Murray: Why problems like homelessness may be easier to solve than to manage. His article focuses on homelessness and air pollution – on how most of the cost of homelessness and comes from a tiny part of the homeless population – and how most air pollution comes from a tiny part of the car population.

Disproportionality is fairly general in many forms of environmental impact. For example, in the Lake Mendota watershed in Wisconsin, most of the phosphorus pollution comes from only a few of the farms in the watershed. However, ecological disproportionality is complicated by the fact that the vulnerability of different sites to human impact also varies – which compounds the disproportionality.

In a recent paper Disproportionality as a Framework for Linking Social and Biophysical Systems (Society and Natural Resources 2006 19:153-173) Pete Nowak, Sarah Bowen, and Perry Cabot write

Early social science was influenced by the work of Adolphe Quetelet, who promoted the idea that the average in a normal distribution represented the ‘‘essence’’ of a social system whereas variance or outliers were viewed as ‘‘accidents’’ in the study of social processes (Kruger et al. 1990). Charles Darwin, on the other hand, viewed variance, or the outlier, as central to understanding evolutionary biological processes. In this article, we have argued that giving more attention to variance across multiple scales can serve as a conceptual bridge between the social and biophysical sciences. Disproportionality is a concept that can bridge disciplines by focusing on the salient interactions between humans and their environments at different spatial and temporal scales.

Nowak et al use the example of farming practices and phosphorus runoff to explore how disproportionality in social and ecological systems intersects. They use the figure below to illustrate how the impact of a behaviour is shaped by place and timing.

Figure (from Nowak’s paper) The combination of typical conservation behavior, exhbiting a skewed normal or log-normal probability distribution, and typical environmental conditions, also exhbiting a skewed normal or log-normal probability distribution of the probability of environmental risk, combines to produce a situation in which a small proportion of inappropriate social behaviors within a particularly vulnerable setting can have a disproportionately large impact on overall environmental quality of an ecological system.

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Thunderstorms and cross-scale land atmosphere couplings

In a Dec 2005 commentary on Feddema et al (2005) The Importance of Land-Cover Change in Simulating Future Climates. Roger Pielke Sr. writes on the role of land use change in shaping thunderstorms:

One example of how land use and land cover affects global climate is the changing spatial and temporal pattern of thunderstorms. Land use and land cover change and variability modify the surface fluxes of heat and water vapor. This alteration in the fluxes affects the atmospheric boundary layer, and hence the energy available for thunderstorms. As shown in the pioneering work of Riehl and Malkus and Riehl and Simpson, at any time there are 1500 to 5000 thunderstorms globally (referred to as “hot towers”) that transport heat, moisture, and wind energy to higher latitudes. Because thunderstorms occur over a relatively small percentage of Earth’s surface, a change in their spatial patterns would be expected to have global climate consequences. The changes in the spatial patterning of thunderstorms result in regional alterations in tropospheric heating that directly change atmospheric and ocean circulation patterns, including the movement and intensity of large-scale high- and low-pressure weather systems. Most thunderstorms (by a ratio of about 10 to 1) occur over land, and so land use and land cover have a greater impact on the climate system than is represented by the fraction of area that the land covers.

NASA has mapped global lighting strikes. The below image shows the global average annual occurrence of lightning at a resolution of ½° by ½°.

Compare this map against Gordon et al’s map of vapour flow changes, and it becomes apparent that some of the areas of strong vapour flow change are in areas of high thunderstorm activity.  It would be interesting to discover what effect the changes in land cover/land use are doing to thunderstorms and if this has any effect on regional/global climate.

Anthropogenic Modification of Vapours Flows and Tipping Points in the Earth System

Compare the map of soil moisture – atmosphere couplings against Gordon et al’s 2005 map of changes in vapour flows in the Human modification of global water vapor flows from the land surface.

PNAS Vapour Flows

Figure shows spatial distribution of net changes in vapor flows between potential vegetation and actual deforested and irrigated vegetation in mm/yr. The aggregated global change as compared with the potential vegetation is small (400 km3/yr), but the map illustrates the large spatial redistribution of water vapor flows from the land surface at the global scale.

Note that the location of increases in vapor flows in irrigation matches up with several of the hotspots identified in the map of soil moisture – atmosphere couplings – central Great Plains of North America, and India. Change occurs also in less intense hot spots appear in South America and China. Consquently, the combination of these two papers predicts that irrigation should have altered the local climate in these regions more than in other regions.

Leverage Points in the Earth System: Soil Moisture

The 2004 Science paper – Regions of Strong Coupling Between Soil Moisture and Precipitation – by Koster et al. used a dozen independent climate models to estimate ‘hot spots’ on Earth’s surface where precipitation is affected by soil moisture anomalies during Northern Hemisphere summer. They propose that these hot spots are, in a sense, land-surface analogs to the ocean’s “El Niño hot spot” in the eastern tropical Pacific.

Soil moisture is a slowly vary aspect of the Earth system (relative to weather). Soil moisture can persist for months. Soil moisture, influences evaporation and other surface energy fluxes can influence weather.

Soil moisture atmospheric coupling

Figure: Hot spots of soil moisture – local precipitation coupling appear in the central Great Plains of North America, the Sahel, equatorial Africa, and India. Less intense hot spots appear in South America, central Asia, and China.

The hot spots are located in regions that in areas that are at intermediate moisture levels. The authors argue that this is because in wet climates, soil water is plentiful and evaporation is controlled not by soil moisture but by net radiative energy. In dry climates evaporation rates are sensitive to soil moisture but they are small. Consquently the biggest impact of soil moisture on evaporation is in the transition areas between dry and wet climates.

What this analysis suggests is that these hotspots are areas in which changes in land use – especially those that alter soil moisture – such as irrigation or land clearing, will have a larger impact of regional climate.

Poverty traps at multiple scales

Welfare dynamics under the poverty trap hypothesis. From Barrett and Swallow 2006

Christopher Barrett and Brent Swallow recently published an interesting paper in World Development on what the authors term ‘Fractal poverty traps’. These are the sort of poverty traps that develops where multiple dynamic equilibria exist simultaneously at multiple scales of analysis. The figure to right shows welfare dynamics under the poverty traps hypothesis.

The authors argue that the strategies that people choose depends on their assets as well as on the risks that they have to deal with, and they give the following example (from Lybbert et al. 1004):

Lybbert, Barrett, Desta, and Coppock (2004) demonstrate that southern Ethiopian pastoralists face two strategies— migratory or sedentarized pastoralism—reflecting two different dynamic wealth equilibria. The dynamic wealth equilibrium associated with migration is relatively high, while that associated with sedentarization is low. Pastoralists prefer not to sedentarize, but if they start off with too small a herd or lose too many animals to drought, disease or (human or wildlife) predators, the superior strategy of transhumant grazing is not accessible to them, for reasons Lybbert et al. (2004) explain. Poorer pastoralists therefore adopt a sedentarization strategy and predictably settle into a low-level wealth equilibrium. The key to understanding the genesis of poverty traps therefore lies in understanding the nature of transitions—or, more importantly, the absence of transitions—between strategies. Why do some pastoralists remain mobile while others do not? Why do some farmers adopt improved production technologies or enter high value-added marketing channels while others do not? What are the barriers that effectively preclude adoption of superior strategies?

According to the authors this is a reason why the UN Millennium Project final report emphasises the need for large initial investments – to push poor individuals, communities, and nations over thresholds so that different strategies become available and feasible. This is particularly important in situations of ‘fractal’ poverty traps:

Small adjustments at any one of these levels are unlikely to move the system away from its dominant, stable dynamic equilibrium. Governments, markets and communities are simultaneously weak in places characterized by fractal poverty traps. No unit operates at a high-level equilibrium in such a system. All seem simultaneously trapped in low-level equilibria.

They suggest four interrelated poverty reduction strategies:

First, it is possible that significant but shortlived transfers to individuals, households, communities, and nations caught in low-level equilibria can enable them to cross crucial thresholds presently inaccessible to them and thereby make it feasible for them to switch to positive growth trajectories that can carry them out of persistent poverty. …

Second, public agencies need to assess the possibilities for eliminating or moving thresholds through interventions at aggregate scales that make previously inaccessible strategies feasible at more disaggregated scales. …
Third, there is a critical need for effective safety nets set above critical thresholds so as to prevent people from falling unexpectedly into chronic poverty. Safety nets that can prevent the non-poor from falling into poverty in response to uninsured shocks should be included in poverty reduction strategies. …

Finally, fractal poverty traps carry important implications for decentralization. … Prioritization exercises must take place at multiple scales and there must be serious attempts to integrate these, not just cursory exercises as has too often been the case.

What Drives Humanity’s Footprint on the Earth?

I recently read a good paper by Richard York, Eugene A Rosa & Thomas Dietz 2003 Footprints on the Earth: The environmental consequences of modernity. American Sociological Review 68(2) 279-300.

The paper uses the statistical analysis of several competing models of what shapes human impact on the earth. The test models of ecological modernization (that democratic capitalist development is developing solutions to environmental problems – i.e. the environmental kuznets curve), political economic (the neo-Marxian treadmill of production), and ecological models (Impact=Population X Affluence X Technology). They found that population and economy size are the best predictors – by far – of a country’s ecological footprint. There is no evidence of ecological modernization, and a little support for political economic models, such as urbanization increases ecological footprint.

They note

Basic material conditions, such as population, economic production, urbanization, and geographical factors, all contribute to environmental impacts and explain the vast majority of cross-national variation in impacts. Factors derived from neo-liberal modernization theory, such as political freedom, civil liberties, and state environmentalism have no effect on impacts.

and conclude

The sobering note from this analysis is our failure to detect the ameliorating processes postulated by neoclassical economics and ecological modernization theorists. This suggess we cannot be sanguine about ecological sustainability via emergent institutional change.

A key consquence is that because of high levels of consumption in affluent nations, even a slow rate of population growth in these nations is at least as great a threat to the environment as is rapid rate of population growth in less developed nations. After all, the footprint of the typical American is nearly 25 times greater than that of the typical Bangladeshi.

ISI selected Footprints on the Earth as a fast breaking paper in Sociology last year.

A bibliography of their related research is avaiable in the STIRPAT Bibliography.

Mapping Possibility of Alternative States in African savannas

At the end of last year M. Sankaran et al had a paper Determinants of woody cover in African savannas (Nature 2005 438(8) 846-849) that maps the possibility of savannas that can exist in alternative states based on rainfall.  This is the first map I have seen that maps the possibility of alternative states at a large  scale.

Map of alt savanna states in africa

Figure: The distributions of MAP-determined (‘stable’) and disturbance determined (‘unstable’) savannas in Africa. Grey areas represent the existing distribution of savannas in Africa. Vertically hatched areas show the unstable savannas (>784mm MAP); cross-hatched areas show the transition between stable and unstable savannas (516–784mm MAP); grey areas that are not hatched show the stable savannas (<516mm MAP).

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Asia’s coastal restoration has on article –The right way to rebuild Asia’s coastal barrier – on plans by tsunami impacted countries to restore coastal ecosystems. It discusses how plans need to consider the economic values of the ecosystem services produced by mangroves as well as the need to design ecologically appropriate mangrove governance strategies.

Now, governments in India, Indonesia, Malaysia, Sri Lanka and Thailand all want to restore what nature once provided for free: they plan to spend millions of dollars replanting thousands of hectares of mangrove forest.

Scientists applaud the ‘greening’ agenda but warn that to succeed, replanting strategies must include workforce training and supervision, maintenance of seedlings, and increased public awareness about coastal land use. Some economists add that we need a better understanding of the relationship between these endangered ecosystems and the communities that rely on them.

“Reforestation is unlikely to succeed in the long term because the underlying policies haven’t changed,” says Edward Barbier, an environmental economist at the University of Wyoming, United States, who has done extensive research on Thailand’s mangroves. Barbier is not surprised that Thailand suffered such extreme damage; since 1961, more than half its mangroves have been removed.

Replanting is critical to restoring ecosystems, he says, but trees alone cannot create the long-term stability needed for sustainable economic growth.

Mangroves tend to be undervalued in economic calculations, which only include the benefits of developing them (such as woodchips or farmed shrimp). This makes it easy for governments to gamble on ‘developing’ the forests. The tsunami clearly raised the stakes — and strengthened the case for protection that ecologists and economists have been making for years.

Previous posts on the tsunami and coastal resilience are: Coral Reefs & Tsunami, Building resilience to deal with disasters, and After the Tsunami.

New Orleans and the ecology of the Mississippi River

Richard Sparks writes about the ecological/geological context in which New Orleans exists, how people have changed them, and what rebuilders should consider. His article is Rethinking, Then Rebuilding New Orleans, in the Winter 2006 Issues in Science and Technology.

His article focusses on the natural forces that have shaped the Mississippi and how humans have shaped those forces. One of the most interesting points he raises is how land cover change, and river management have radically changed the sediment load of the Mississippi, shifting the balance between land building and subsidence in the delta. In other words flood protection higher in the river has made lower portions of the river more vulnerable to flooding.

sediment loads carried by the Mississippi River 1700 & 1980-1990Figure: The sediment loads carried by the Mississippi River to the Gulf of Mexico have decreased by half since 1700, so less sediment is available to build up the Delta and counteract subsidence and sea level rise. The greatest decrease occurred after 1950, when large reservoirs constructed trapped most of the sediment entering them. Part of the water and sediment from the Mississippi River below Vicksburg is now diverted through the Corps of Engineers’ Old River Outflow Channel and the Atchafalaya River. Without the controlling works, the Mississippi would have shifted most of its water and sediment from its present course to the Atchafalaya, as part of the natural delta switching process. The widths of the rivers in the diagram are proportional to the estimated (1700) or measured (1980–1990) suspended sediment loads (in millions of metric tons per year).

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Inequality of Climate Change Impacts

Jonathan Patz et al have recently published a review paper on the Impact of Regional Climate Change on Human Health, in a special feature on regional climate change in the Nov 16th issue of Nature.

The article shows that climate change is already a substantial factor shortening people’s lives. The authors estimate that climate change kills an excess 154 000/yr. This mortality compares with 6 million deaths/yr caused by childhood and maternal malnutrition (the largest proportion of mortality) and with 109 000 deaths/yr from carnciogen exposure (data from Rodgers et al 2004 Distribution of Major Health Risks: Findings from the Global Burden of Disease Study. PLOS Medicine pdf)

Climate change deaths are estimated to occur primarily due to increases in malnutrition (77 000 deaths), diarrhoea (47 000 deaths), and Malaria (27 000 deaths). However, the health impacts of climate change vary greatly across the world. In general the areas, least responsible for changing the climate, are suffering the most deaths from climate change. These deaths are concentrated in poor countries, with about half of these deaths occuring in poor countries in S and SE Asia (specifically Bangladesh, Bhutan, Democratic People’s Republic of Korea, India, Maldives, Myanmar, Nepal), which are home to 1.2 billion people.

The mismatch between the countries most responsible for producing climate change and its impact is shown in the two maps below. The first map shows CO2 emissions/capita in 1998 from WRI data, while the second shows the estimated numbers of deaths per million people that could be attributed to global climate change in the year 2000 (From Patz et al). The mismatch be further exagerated if the cumulative CO2 emissions/capita of nations, a better indicator of national responsibility for climate change, were shown.

national level co2 emissions per capita 1998 Drawing from data from the World Health Organization, the map was also created by Patz's team. Map courtesy the Center for Sustainability and the Global Environment.

[click on a map to see a larger version]

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