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Sustain to gain: February 2010 Archives

Carbon dioxide is not the only greenhouse gas. Coemitted air pollutants also significantly affect global climate. By various interactions, their absolute effect can be complicated to evaluate. In principle, however, most air pollutants have a relatively short time span in the atmosphere, and hence, can be classified as short lived species. Many air pollutants, including organic aerosols have a global cooling effect, whereas black carbon and ozone contribute to global warming.  The effect of the short lived species is not marginal. In fact, their combined radiative forcing may outweight that of carbon dioxide (Forster et al., 2007). In view of this observation, there is increased attention on the mitigation potential of some air pollutations, such as ozone and black carbon, short lived species with high radiative forcing. On the other hand, there are other aerosols, excluding black carbon, which exert a cooling effect that may have masked about 50% of the global warming by GHG. The fight against air pollution and for public health can, hence, have an unwanted impact by inducing accelerated global warming. Starting with this background, Unger et al. from NASA ask in PNAS in their article Attribution of climate forcing to economic sectors the following question: How is the total radiative forcing effect organized according to economic sector, the drivers of emissions?

The authors point out that emissions of black carbon (positive RF) and organic aerosols (negative RF) are often coupled. Hence, the ratio between both emittants is important to evaluate the total radiative forcing in a specific sector. An analysis of sectors according to this ratio reveals significant differences across sectors:

  •  There are sector such as the power industry that have high emissions of species with both positive and negative radiative forcing.
  •  Other sectors, such as road transport, are dominated by species with positive radiative forcing. More specifically, the ratio between black carbon and organic carbon aerosols is relatively high in road transport.

The accumulated climate impact over all sectors is visualized in the figure below (Source: Unger et al., 2010). In fact, in the short term (2020), road transport dominates the accumulated climate impact. In the long run (2100), the power sector dominates as greenhouse gases persists significantly longer in the atmosphere than short lived species.

Climate impact of economic sectors in 2020 and 2100.

From this technical analysis, effective  climate change mitigation can most easily be obtained in on-road transportation - with significant co-benefits as air pollutants from transport are more harmful than from other sectors. This is for example due to a higher intake fraction (fraction of pollutants that is inhaled, e.g. Marshall et al., 2005), but can have more general benefits for public health and overall mobility (Creutzig and He, 2009). However, from a climate perspective road transportation is underregulated. For example, in Europe road transport is not part of the emission trading scheme, and, by this, is positively discriminated against electrified rail transport. A clever mix of instruments that prices the harmful parts of mobility while increasing its beneficial aspects (e.g. accessibility, thence, could have a near and long term positive impact).

Thanks to Jan Minx for pointing out the PNAS article.


Forster P, et al. (2007) Changes in Atmospheric Constituents and in Radiative Forcing, in Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, eds Solomon S, et al. (Cambridge Univ Press, New York)

Unger, N.,  Bond, T. C., Wang, J. S., Koch, D. M., Menon, S., Shindell, D.T., Bauer, S. (2010) Attribution of climate forcing to economic sectors PNAS 2010 : 0906548107v1-6

Marshall, J.D., Teoh, S.K., and Nazaroff, W.W. (2005) Intake fraction of nonreactive vehicle emissions in US urban areas. Atmospheric Environment 39 (7), 1363

Creutzig, F. and He, D. (2009) Climate change mitigation and co-benefits of feasible transport demand policies in Beijing  Transportation Research D 14: 120-131

"Global Sustainability - a Nobel Cause", is the title of a book that just has been published by Cambridge University Press. A number of nobel price winners and eminent scientists in sustainability research gathered to write up their thoughts on sustainability. This book certainly does not fulfill coherent scientific standards (peer-reviewed, novel insights) but is very promising in bringing some relatively simple but profound thoughts together. Also, as a clear pro: this book is freely available online, and individual chapters can be downloaded as pdf.

What can we, then, learn from this book? Let us start with Geoffrey West's observation that current scientific endeavors have, to a large degree, failed to come to grips with the essence of the long-term sustainability challenge: the pervasive interconnectedness and interdependency of energy, resources, environmental, ecological, economic, social, and political systems (West, 2010; see also Creutzig and Kammen 2009). My own specific example of this statement (Creutzig and Kammen, 2010) looks at the specific examples of biofuels, rephrasing the by now established view that a simple-minded view of biofuels as zero-carbon sources of energy misses the point, as a) the carbon content can be not only significant but even surpassing that of conventional fuels and b) a number of additional sustainability issues such as biodiversity loss, deforestation and food insecurity threaten to diminish any feasible positive impact on the climate change front.

So what is the possibility and challenge of using a coarse-grained systemic approach that builds on, but also goes beyond, piece-meal wise investigations? Wolfgang Lucht calls for the enterprise to construct new mental images of the whole - or taking a crude look at the whole as Murray Gell-Mann says - that must be founded in rational analysis and, equally important, cultural production (Lucht, 2010). In fact, according to Lucht, a controlled transition in the interlinked social-environmental world system is to be achieved, only by making transitional progress not just in the environmental domain, where the impacts have to be lessened, but also in the social domain, where the problems have their origin. This transitional progress building on rational-scientific insights (that transcend the techno-economic totalitarian aspects of enlightenment) then could enable a sustainable transition path as depicted in the figure below.

(taken from Lucht, 2010, partially based on Schellnhuber, 1999) 

The small problems left are (1) to fill these grand themes with contents and (2) to integrate the findings into the "societal self constructions that dominate human processes" (Lucht, 2010). Regard the first issue, my blogging colleague Carey King suggests to look at EROI - energy return on energy invested -, noting that EROI is lower for renewables than for fossil fuels with respect to human time scales, and that a future lower EROI implies a reduction in societal complexity (this conjecture requires more thoughts though). Geoffrey West points at the fundamental nature of time scales, explaining the supra-linear scaling of agglomerations, and hence supra-exponential growth that requires an ever accelerating rate of innovation (not sustainable). These spotlights indicate the pressing need for a consistent growth theory which includes natural capital degradation (and appropriate ressource flow exploitation), agglomeration dynamics and structural change, the clear definition of a perspiciuous welfare function of sustainability, and finally a proposal for a non-catastrophic deceleration of the human socio-economic system.


Bettencourt, L. M. A., Lobo, J., Helbing, D., K├╝hnert, C. and West, G. B. (2007) Growth, innovation, scaling, and the pace of life in cities. Proceedings of the National Academy of Sciences of the United States of America, 104(17), 7301- 6.

Creutzig, F.,  Kammen, D (2009) The Post-Copenhagen Roadmap Towards Sustainability: Differentiated Geographic Approaches, Integrated Over Goals INNOVATION, Vol 4 (4): 301-321

Creutzig, F.,  Kammen, D (2010) Getting the carbon out of transportation fuels. In H. J. Schellnhuber, M. Molina, N. Stern, V. Huber & S. Kadner (Eds.), Global Sustainability - A Nobel Cause. Cambridge: Cambridge University Press, UK.

Schellnhuber, H. J. (1999). Earth System Analysis and the Second Copernican Revolution. Nature 402, Suppl., C19 - 23.

West, G. (2010) Integrated sustainability and the underlying threat of urbanization. In H. J. Schellnhuber, M. Molina, N. Stern, V. Huber & S. Kadner (Eds.), Global Sustainability - A Nobel Cause. Cambridge: Cambridge University Press, UK.