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Tuesday, September 4, 2012

Not enough water: food production, carbon sequestration and climate change

A new study has found that there is not enough freshwater to meet the anticipated competing demands of water for food production for the global population of about 9 billion by 2050 and water for optimal growth of biomass for carbon sequestration for climate mitigation. As food production is essential, the authors of the study conclude that large scale carbon sequestration may not be realistic as a major method of climate mitigation, and we may need to rely more on direct reduction of emissions.

We rely on freshwater to drink daily, to bathe in and flush our toilets with; but also for growing our veggies and crops; to grow feed for our animals; for healthy riparian and aquatic habitats and ecosystems; for our forests and wild places to sequester carbon dioxide as biomass carbon sinks. But increasingly we are approaching boundaries and limits on the amount of freshwater available and the trade-offs involved in competing uses.

We see some of the debate on trade-offs in water use in the Murray Darling Basin plan in Australia. The inland river waterways and wetlands system has become extensively degraded through over allocation of water for human consumption, industrial and mining use, and irrigation for agriculture over the last century. Healthy rivers and wetlands require environmental flows to maintain natural ecosystems to support wildlife, water quality and to sequester carbon.

On a global level, the researchers assessed the safe planetary boundary level of freshwater use at about 5,000 cubic kilometers (1,200 cubic miles) per year. Current water use is at the level of 2,600 cubic kilometers (624 cubic miles) per year. Achieving global food security for 9 billion people by 2050 and maximizing carbon sequestration together would require increasing water consumption by 3,250 cubic kilometers (780 cubic miles) per year, which would total 5, 850 cubic kilometers (1,404 cubic miles) per year, much greater than the assessed planetary boundary.

The study by Rockstrom et al. from the Stockholm Resilience Centre, Stockholm University - The planetary water drama: Dual task of feeding humanity and curbing climate change (abstract) - was published in Geophysical Research Letters in August 2012. From the article abstract:

"The paper shows that the consumptive water use involved in the dual task would both transgress the proposed planetary boundary range for global consumptive freshwater use and would further exacerbate already severe river depletion, causing societal problems related to water shortage and water allocation. Thus, strategies to rely on sequestration of CO2 as a mitigation strategy must recognize the high freshwater costs involved, implying that the key climate mitigation strategy must be to reduce emissions."

The study authors stress the need for societies to recognize the trade-offs between using water for food production and for increasing carbon sequestration through biomass. They conclude that since food production is essential, large-scale carbon sequestration through increasing biomass might not be realistic as a major mode of climate change mitigation.

Though food production is important, that doesn't mean we should ignore maintaining the health of our river and wetland systems as carbon sinks. Healthy river and wetland habitats provide direct economic value through tourism and recreation and indirect economic contributions through water filtration, flood control, water storage and habitat preservation. (See New study estimates economic value of wetlands conservation - 2010)

Maintaining the health of our wetlands, or restoring them to health, also provides a natural carbon sink capacity, according to a scientific study published in Jan 2012 - Freshwater wetlands are important carbon sinks. Keeping this carbon sequestration potential should be paramount.

As optimal biomass carbon sequestration on the global level looks unlikely to be achieved due to the trade-offs with food production necessary over water use, it all comes down to the need to reduce our carbon emissions directly and to increase the transition from carbon intensive energy and transport to renewable and low carbon energy and transport. We could have a carbon neutral solar and wind powered world in 20 to 40 years if we apply our technological and economic resources to the task. Here in Australia Beyond Zero Emissions working with Engineers from Melbourne University devised a plan to achieve Zero carbon emissions by 2020 from stationary energy sources. Not only would the implementation of such plans drastically reduce emissions, they would also stimulate employment and transform our depressed economies.

Public education and consultation important in resolving water choices

Fresh water has tended to be seen as a cheap, readily available resource. It may be limited in certain regions or times of the year, but it is still relatively abundant on a global level. Increasingly we are realizing the true cost of freshwater, as we are forced to trade-off important uses. Solving water security and resolving the trade-off choices is complex. This is seen in two long term water security projects for Melbourne: a north-south pipeline to bring water from the Goulburn-Murray river basin for use in Melbourne which was widely criticised and subsequently shutdown by the Baillieu Government in November 2011; and the decision to construct a desalination plant at Wonthaggi. (see Solving water security: don't ignore the public at The Conversation)

We are also seeing conflict between excessive groundwater use in mining and use of freshwater and chemicals in hydro-fracking techniques to extract coal seam gas (CSG) increasing the conflict with human and agricultural use of water resources.

Agricultural crop production for manufacture of biofuels is another issue of some concern which involves assessing the water and carbon trade-offs involved. The authors of this study identify "the need to analyze both water and carbon tradeoffs from anticipated large scale biofuel production climate change mitigation strategy, to reveal gains and impact of this in contrast to carbon sequestration strategies."


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