Addicted to fossil fuels

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Stratospheric Sulfur Injections

Today’s post focuses on an article by Crutzen (2006) with the title ‘Albedo enhancement by stratospheric sulfur injections: a contribution to solve a policy dilema?’. Crutzen describes the very controversial technique of actificially adding sulfur particles to the stratosphere to increase albedo.

Human emissions do not only consist of CO₂. Our industries also emit SO₂. Once emitted in the atmosphere SO₂ is processed into sulfate particles, which act as cloud condensation nuclei. More clouds can be formed, which causes a backscattering of incoming solar radiation and thereby enhances albedo. This can in consequence cool the earth’s surface and slow down global warming. The effect of great amounts of sulfur could be wittnessed after great volcanic eruptions e.g. Mount Pinatubo in 1991. The following diagram shows the reduced solar radiation that is transmitted after great volcanic eruptions:

(source: http://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols)

The idea of this geoengineering technique is now to artificially inject SO₂, S₂ or H₂S ‘near the tropical upward branch of the stratospheric circulation system’ (Crutzen 2006). This way the particles are transported into the stratosphere where they remain for 1-2 years. In lower heights in the troposphere their residence time is shorter and therefore more sulfur would be needed to achieve the same effect. So far this technique sounds like a solid plan, but it is not as easy as it seems to be: Sulfur can cause serious damage to the environment and to human’s health. It can e.g. cause premature death, “more than 500,000 […] per year worldwide (Crutzen 2006).

The dilemma is now that what is good for our health has negative effects in terms of climate change. A cleaner air can indeed lead to an additional warming of the earth’s surface. Crutzen estimates that a complete clean air leads to 0.8K warming of surface air temperature. However one suggestion is to clean the lower atmosphere level, which directly influence human’s health, and to inject sulfur above in the statosphere. Crutzen calculates the cost of stratospheric sulfur injections that are required to compensate for the additional warming and estimates a total price of US $25–50 billion/yr.

But is this really an option? As good as the intended effect is, we have to consider the negative side effects. In my opinion it is no solution to put at risk human health in this way. Sulfur particles may be injected in to the stratosphere but they will eventually loose height and affect us. I think the general idea to reflect sunlight is good, but there have to be other ways. Another method proposed is e.g. using mirrors in space or in the atmosphere. I want to discuss if this method might be an alternative in a later post.

What do you think about stratospheric sulfur injections? A way to save our climate or a way to destroy health and environment?

Literature:

Crutzen (2006) ‘Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?’ Climatic Change, 77 (3-4), 211-219.

Available online: http://www.springerlink.com/content/t1vn75m458373h63/ 

The Anthropocene

Today I want to present two articles by Steffen et al. (2007 and 2011), which give some background information on my topic geoengineering. They both deal with the Anthropocene, a term introduced about 10 years ago, describing the new era in Earth history which is strongly influenced by humans. The term is still not officially defined, but it generally describes the time until now where human influences on the Earth system became so strong and global in scale that they are able to modify the ‘great forces of Nature’ (Steffen et al. 2011: 843). The exact starting point of this time described as a new geological epoch is still discussed. Some scientists are of the opinion that clearing of forests 8000 years BP and first agriculture 5000 years BP are the first measurable human influences on e.g. the global carbon cycle. Human influence is also often linked to the extinctions of the Pleistocene megafauna. (Steffen et al. 2011)

However most scientist hold the opinion that the most determining factor for global changes in natural cycles is the industrialisation and the developments that followed. Whichever opinion is right, there are clear evidences for a strong human influence since the start of the Industrial Revolution 1700. The rise in atmospheric CO₂ is often taken as an indicator for human influence, as it is a result of fossil fuel use and other human activities e.g. deforestation  (Steffen et al. 2007 and 2011).

Due to the ability of natural carbon sinks to delay the response in CO₂ concentration in the atmosphere, the value for 1850 (285 ppm) is still within the natural variability of the Holocene. The human influence became visible later on: CO₂ concentration rose to 311 ppm in 1950, which is clearly beyond natural fluctuation (Steffen et al. 2007).

The time after 1950 is also described as the second stage of the Anthropocene or the Great Acceleration. The reason for this are the dramatic increases in the observed human impacts. ‘Every indicator of human activity underwent a sharp increase in rate around 1950’ (Steffen et al. 2011: 849). Changes can be seen e.g. in population, urban population, water use, transport or tourism:

source: Steffen et al. 2011, figure 1, p. 842

The same trends can be observed in natural cycles or events e.g. CO₂, N₂O and CH₄ concentrations in the atmosphere, flooding events or species extinctions:

source: Steffen et al. (2011), figure 1, p. 852

With those findings the human influence cannot be denied. The atmospheric CO₂ concentration reached 379 ppm in 2005 (Steffen et al. 2011), which is 102 ppm higher than the pre-industrial value of 1700. That means geoengineering techniques that aim so sequester CO₂ would have to deal with this amount of carbon dioxide, if we want to return to pre-industrial levels. 

The newer article from 2011 also highlights some points concerning geoengineering. It holds a rather critical view and reminds the reader, that side effects also have to be kept in mind. Steffen et al. (2011) chose the example of artificially added aerosols to illustrate the topic of geoengineering, but I don’t want to go into depth this time, as this is another technique that I want to present later in my blog. All in all the authors stress that further research is still needed before a decision on geoengineering can be made. In addition there are ethical, social and organisational/governmental questions that still need to be answered (Steffen et al. 2011).

Literature:

Steffen, W., Crutzen, P. and McNeill, J. (2007) ‘The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature?’, AMBIO, 36 (8), 614 – 621.
available online: http://www.bioone.org/doi/abs/10.1579/0044-7447(2007)36%5B614:TAAHNO%5D2.0.CO;2

Steffen, W., Grinevald, J., Crutzen, P. and McNeill, J. (2011) ‘The Anthropocene: conceptual and historical perspectives’, Philosophical Transactions of The Royal Society, 369, 842-867.
available online: http://rsta.royalsocietypublishing.org/content/369/1938/842.short

Public supports geoengineering. Really??

This comic that I found online ties in with my last posts and the idea of planting trees to offset some of the impacts of climate change:

source: http://www.cartoonmovement.com/cartoon/3058

It holds a rather critical view towards geo-engineering. But is that the overall public opinion? A recently published survey by A M Mercer, D W Keith and J D Sharp (available online) in Environmental Research Letters investigated the public understanding and opinion on geo-engineering, in this case especially on solar radiation management. When reading the results of their survey the first thing that stands out is that, as it seems to me, only a minority of people are familiar with geoengineering methods. While 20% stated that they have heard about geo-engineering before, only ‘8% of the population can correctly describe geoengineering’ (Mercer et al. 2011). According to the survey more people are familiar with the term climate engineering (45% were able to define it). When first asked if geoengineering should be a solution to global warming, respondents could give answers on a four-point scale (‘1 = strongly disagree and 4 = strongly agree’, Mercer et al. 2011). The mean answer was 2.35, which is relatively undecided with tendency towards disagreement. However a quarter of respondents selected unsure, which I think confirms that there is probably a lack of information in general public. While several newspapers or news websites like the Guardian or BBC report about this survey, I think that headlines should be treated with care: According to the survey ‘72% somewhat or strongly support’ (Mercer et al. 2011) allowing research on solar radiation management. In the press and in many headlines or blogs online on the other hand it appears that 72% generally support geoengineering. This again could give a false idea about what is actually said in the study.  There are already some strong reactions e.g. this video I found on youtube. It refers to the BBC article from last week.

http://www.youtube.com/watch?v=PfIpEl-WKrM

I think it is very important to pronounce statements like this carefully to prevent misunderstanding. It is important to inform the public about what geoengineering methods are and what effects they aim at. As the survey also shows that scientists are considered trustworthier than governments, the source of information could also influence respondents. 64% of respondents supported the statement that ‘humans should not be manipulating nature’ (Mercer et al. 2011) and 2/3 doubt that one technology alone is sufficient to fix the earth’ complicated climate. From my point of view the survey shows that there is still a lack of information in general public, but that the majority of people would support further research – this does not necessarily imply the implementation of geoengineering methods.

So what do you think about geoengineering in general? Is it a solution to our problems? And is it even possible to come to a definite conclusion?

Literature:

A M Mercer, D W Keith and J D Sharp (2011) 'Public understanding of solar radiation management', Environ. Res. Lett., 6 

Discovery Project Earth

The following video shows a brief summary of Dr. Mark Hodges' idea of planting trees on a grand scale via aircrafts.


Source: http://dsc.discovery.com/videos/discovery-project-earth-raining-forests-in-a-nutshell.html

Planting trees?

Another way that was proposed to mitigate climate change is to 'simply' plant more trees. Carbon dioxide circulates between different reservoirs. Forests currently cover roughly 1/3 of the world’s land surface and are the most significant terrestrial carbon store (Eliasch 2008). Trees sequester CO₂ through photosynthesis and store it in their biomass. This is the reason why one geo-engineering approach suggest to plant more trees to compensate for anthropogenic CO₂ emissions. But can that really work?

When examining this approach it falls into place that CO₂ reduction is not the only impact of planting new forests. Other biophysical effects like changes in evapotranspiration, cloud formation and albedo also have to be taken into account (Bala et al. 2007, Betts 2000, Gibbard et al. 2005).

Albedo effects are especially significant in boreal forest regions. Planting trees leads to a decrease in albedo most notably in winter, because bare ground, lower vegetation structures and snow-covered ground have a higher albedo than forests. Afforestation therefore has a warming effect at high latitudes and is therefore counterproductive,  because the albedo effect outweighs the cooling effect though carbon sequestration (Bala et al. 2007, Betts 2000, Gibbard et al. 2005).

Tropical forests at low latitudes in contrast have higher rates of evapotranspiration and for this reason more clouds are formed. In addition to the carbon induced cooling effect, evapotranspiration leads to a cooling and cloud formation enhances albedo. Thus the net effect of afforestation at low latitudes is cooling (Bala et al. 2007, Betts 2000, Gibbard et al. 2005).

Temperate forests take an almost neutral position in this geo-engineering method. According to Bala et al. (2007) warming effects due to a albedo descrease and cooling effects carbon sequestration even out.

The following graphic taken from Bonan (2008) illustrates the environmental impacts of the three mentioned forest types (A-C) and their geographical distribution:

There is still a need for further research on the quantity of effects and on comparison of different models, but so far the conclusion can be drawn that forestation CAN have a positive impact on mitigating climate change, IF applied in the right place. Afforestation on a large scale at low latitudes can have a cooling effect, while it would only increase warming at higher latitudes.

Literature:

• Bala, G., K. Caldeira, M. Wickett, T. J. Phillips, D. Lobell, C. Delire, and A. Mirin (2007): Combined climate and carbon cycle effects of global deforestation, Proceedings of the National Academy of Sciences, 104(16), 6550-6555. Available online: http://caos.iisc.ernet.in/faculty/gbala/pdf_files/Bala_etal_PNAS2007.pdf

• Betts R.A. (2000): Offset of the potential carbon sink from boreal forestation by decreases in surface albedo, Nature, 408, 6809, 187-190 Available online: http://www.nature.com/nature/journal/v408/n6809/full/408187a0.html

• BonanBetts, G.B. (2008): ‘Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests’, Science, 320, 1444 - 1449. Available online: http://www.sciencemag.org/content/320/5882/1444.full

• Eliasch, J. (2008): Climate Change: financing global forests: the Eliasch review, London: Earthscan. Online version: http://www.official-documents.gov.uk/document/other/9780108507632/9780108507632.pdf

• Gibbard, S. et al. (2005): Climate effects of global land cover change, Geophysical Research Letters, 32, 23. Available online: http://www.agu.org/pubs/crossref/2005/2005GL024550.shtml

Impact of cloud seeding on hydrological cycle

Today I want to briefly amend another aspect to the method introduced in my last post. The study by Bala et al. (2010) deals with impacts of cloud-seeding on the hydrological cycle. The method of cloud-seeding produces low-level clouds only above the ocean while the cloud layer above land remains unmodified. That means solar radiation is only reduced over the oceans. Nevertheless this geo-engineering method has an impact in the whole hydrological system. The article further describes that reflecting radiation via maritime clouds leads to a decrease in global mean precipitation and evaporation (1.3%) but an increase in runoff over land (7.5%) and land-mean precipitation. According to the study this is a result of the cooling of the atmosphere over the oceans which leads to a ‘monsoonal circulation with rising motion over land (...), and sinking motion over ocean with associated statistically significant increases in precipitation over land.’ (Bala et al. (2010): 927)

The study emphasises that an enhancement of albedo does not only have a cooling effect for our climate, but that that there are other side effects that have to be kept in mind. It is mentioned that those results contrast with previous studies, which is why further research is necessary before a decision on the implementation of cloud-seeding on a global scale is made.

Literature:

Bala, G., Caldreia, K., Nemani, R., Cao, L., Ban-Weiss, G., and Shin, H.-J.: Albedo enhancement of marine cloud to counteract global warming: impacts on the hydrological cycle, Clim. Dy- nam., doi:10.1007/s00382-010-0868-1, 2010.

available online: http://www.springerlink.com/content/9569172415150486/