The world faces a constant dilemma – we require fresh water both as a source of drinking water and to produce food to support an ever increasing human population, yet water is also required to support the growth of natural vegetation, such as forests, which are essential for absorbing carbon dioxide from the atmosphere to help reduce the rate of global warming. But is there sufficiently abundant water available on Earth to adequately supply both these demands?

Food Production and Biomass for Carbon Sequestration Compete for Water

A recent study conducted by a team of researchers from Stockholm University, Sweden, has estimated the water consumption required to support a projected total world population of 9 billion people by 2050 and how much water will be required to support the biomass that is necessary to meet the carbon sequestration demands of our ever warming planet. During their analysis, the researchers looked at a number of thresholds that if water consumption remained within, the Earth's ecological systems would cope sufficiently. However, overstepping these threshold limits could result in sudden changes, which could be irreversible and have dire consequences for ecosystems and people dependent upon them. for example, if excessive amounts of freshwater are withdrawn from rivers, water levels can be reduced to levels that will result in ecological collapse of these aquatic ecosystems.

Food and Carbon Sequestration Water Demands Exceed Earth’s Water Constraints

The researchers projected that in order to provide sufficient water to achieve global food security, while at the same time maintaining the goad of carbon sequestration through forestry programs, an annual increase in water consumption of 780 miles³ (3,250 kms³) would be required. When this figure was added to the current annual global water consumption figures of 624 miles³ (2,600 kms³) it resulted in an unsustainable figure of 1,404 miles³ (5850 kms³) of water required annually, which according to their study, would be beyond the safe annual threshold limits of 1,200 miles³ (5000 kms³). Transgressing these threshold limits would threaten aquatic ecosystems and result in water shortages, which could result in social-ecological problems as people struggle to meet both their basic food and water requirements.

Projected Biomass Water Consumption Aggravates Current Regional Water Shortages

This study stresses the need for communities to understand that there is a trade-off between allocating water to produce food to feet the people of the world and allocating water to sustain biomass to remove atmospheric carbon dioxide in an effort to mitigate climate change. As food production cannot be reduced without reducing food availability and food security, this highlights the fact that in the long-term, greening projects alone will not be a realistic method to sufficiently counter the effects of carbon emissions, as they compete for food for valuable water resources. While greening projects certainly have their benefits, which aside from carbon sequestration, include restoring habitat in an effort to maintain biodiversity, we need to realize that the most feasible way to reduce carbon emissions is to stop emitting carbon; or at least to make a concerted effort to reduce these emissions at the source, rather than relying on carbon sequestration by photosynthesizing plants to reduce atmospheric carbon.

Journal Reference

The planetary water drama: Dual task of feeding humanity and curbing climate change, Geophysical Research Letters, doi: 10.1029/2012GL051688