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/

Seeding maritime clouds to enhance albedo?

The first method I want to focus on tries to increase the earth’s albedo to prevent a further rise in global temperature as presented in Latham et. al (2008). In order to achieve this goal scientists try to seed low-level maritime stratocumulus clouds.

Clouds can contribute to the cooling of the earth’s temperature through albedo, but can also have a warming effect by reflecting long-wave radiation from the surface into space. The method of seeding clouds seeks to increase the albedo and thus the cooling effect of the cloud layer by increasing the natural droplet number concentrations. (Latham et al. 2008). This methods works as follows:

• Seawater droplets from the ocean surface are disseminated into the air to form cloud condensation nuclei (CCN). CCNs are solid particles in the atmosphere that are needed for water to coalesce droplets. In this case salt, that remains after the disseminated water particles evaporate, acts as the solid particle.
• Thus additional droplets can be formed and the enhanced total droplet surface of a cloud leads to an increase in albedo.
• As an additional effect it is possible that clouds are more stable and persist longer.
• The technical implementation of cloud-seeding requires ships for the dissemination of seawater. Scientists suggest to use ships with special ‘Flettner rotors’ which allow unmanned and remote-controlled vessels. These rotors are ‘vertical spinning cylinders that use the Magnus effect to produce forces perpendicular to the wind direction’ (Salter et al. (2008)).

 (source: Salter et al. (2008): 3998, figure 8)

Latham et al. suggest that ’doubling of the natural droplet concentration (...) would produce cooling sufficient roughly to balance the warming associated with CO₂ doubling.’ (Latham et al. (2008): 3971)

According to the essay of Latham et al. the method is not yet fully developed and ready to be applied at a global scale, but the authors are positive that cloud-seeding could stabilise the average global temperature, once all open questions are answered.

To get a better insight in how the implementation of such an idea could look like I recommend watching the following BBC report. It summarises the idea of cloud-seeding and shows the technical implementation:

So could this method really stop global warming? On the first sight it sounds like a ‘mild’ form of geo-engineering as no chemicals or big machinery is used and the dissemination of seawater can be stopped relatively quick. But on the other hand there may be other side effects caused by a higher salt concentration in the air. This could have an influence on ecosystems and soils if transported towards the land. I think these side effects need to be considered but if they are not significant and cloud-seeding really has good results in enhancing albedo it may be a good way to at least slow down global warming.
What do you think? Should we use this method in future times?

Literature:

• Latham, J., Rasch, P., Chen, C.-C. J., Kettles, L., Gadian, A., Gettelman, A., Morrison, H., Bower, K. & Choularton, T. (2008): Global temperature stabilization via controlled albedo enhancement of low-level maritime clouds. Phil. Trans. R. Soc. A 366, 3969–3987. Available online: http://rsta.royalsocietypublishing.org/content/366/1882/3969.abstract?sid=43023fa5-b6bb-436b-9101-8ab82698ff60

• Salter, S., Sortino, G. & Latham, J. (2008): Sea-going hardware for the cloud albedo method of reversing global warming. Phil. Trans. R. Soc. A 366, 3989–4006. Available online: http://rsta.royalsocietypublishing.org/content/366/1882/3989

What is geoengineering?

Before focusing on a particular method I first want to give a brief overview over geoengineering. It is a frequently-used and yet very vague term. But what exactly does geoengineering mean? What methods are described as geoengineering? Although there is no standardised definition for the term one can find many attempts to define it. David W. Keith gives a short and nicely illustated overview over what is implied in the term ‘geoengineering’: ‘Geoengineering is planetary-scale environmental engineering, particularly engineering aimed at counteracting the undesired side effects of other human activities’ (Keith 2001: 420). This comprises all actions that intent to have an effect on environmental conditions and that operate at a large (i.e. global) scale. In most cases specific sophisticated technology plays an important role in realising a geoengineering method. However the distinction between geoengineering methods and other methods that do not meet both of the two mentioned conditions is not always clear.

The term geoengineering was first used in the early 1970s, as scientists realised that using fossil fuels has an impact on our environment and climate. They tried to inject CO₂ into the deep ocean. The term became then more popular in the 1990s in discussions about climate change. (Keith 2000: 248)

Geoengineering focuses on different aspects that could help to slow or stop global warming e.g. reducing the solar radiation by using giant mirrors in space, fine particles in the atmosphere or artificial clouds. Other methods focus on decreasing the amount of CO₂ in the atmosphere by enhancing oceans sinks through fertilization with iron, terrestial sinks or biological sinks e.g. forests.

There are various ways in which scientists try to find a solution to global environmental change. Which methods are feasible and can actually be successful remains to be seen.

Literature:


      D. W. Keith (2001). Geoengineering. Nature, 409: 420.

PDF available online:

http://people.ucalgary.ca/~keith/papers/37.Keith.2001.Geoengineering.e.pdf


David W. Keith (2001). Geoengineering and carbon management: Is there a meaningful distinction? Greenhouse Gas Control Technologies: Proceedings of the 5th International Conference. D. Williams, B. Durie, P. McMullan, C. Paulson and A. Smith eds., CSIRO Publishing, Collingwood, Australia, p. 1192-1197.

PDF available online:

http://people.ucalgary.ca/~keith/papers/41.Keith.2001.GeogineeeringAndCarbonManagment.f.pdf

Plan B for Climate Change?

This blog is part of the course ’Global Environmental Change’ at University College London. I chose the title for my blog ‘Plan B for climate change’ because finding ways to combat global warming and man-made climate change is one of the biggest challenges we have for the future. In this context geoengineering has become a very popular term and various ways of changing the current trends are discussed among experts and even in general public. Therefore I will have a closer look at different geoengineering techniques, their function and feasibility as well as benefits and/or disadvantages to see if geoengineering could really be a plan b for our environment.