As far as metaphors go, it is fair to describe the global water cycle as the bloodstream of the biosphere. It’s an important regulator of the Earth's climate as it helps maintain the stable environmental conditions humanity has enjoyed during the Holocene.
An excessive use of freshwater has a negative impact on this function. If too much is taken out the cycle will change. The consequences are dramatic for the biosphere and the earth’s climate.
Taking out more than you have
That is why freshwater is identified as one of the nine planetary boundaries. The message is clear: If the outtake increases beyond the proposed boundary for consumptive freshwater use the risk of abrupt and irreversible changes in the climate and ecosystem services is believed to increase dramatically.
A recently published study in Geophysical Research Letters analyses the potential conflict between feeding a growing population and sequestering carbon to mitigate climate change.
The article, which is written by centre researchers Malin Falkenmark, Johan Rockström and Louise Karlberg together with Mats Lannerstad from Stockholm Environment Institute, reveals that the combined use of water for both food production and curbing climate change transgresses the proposed boundary and will further exacerbate already severe river depletion.
Hungry stomachs, warming world
By 2050 the world’s population is likely to have reached nine billion people. That is, nine billion stomachs that should not go hungry. This means that food production will need to increase, and consequently an increase in use of freshwater. Meanwhile, we currently rely on extensive amounts of freshwater for sequestration of carbon, to decrease carbon dioxide in the atmosphere and mitigate climate change.
In their study, Falkenmark and her co-authors analysed the potential change in consumptive water use between today and 2050, in a world with nine billion people where the daily caloric intake is 3000 kcal, corresponding to that in Brazil, China and Mexico in 2009. They then added to that the estimated amount of freshwater needed for carbon sequestration.
While counting on increased efficiency in water use related to farming, and calculating sequestration potential equivalent to that of tropical regions, the figures do not add up.
Focus on the emissions
"It is clear that the consumptive use of freshwater involved in the dual task of carbon sequestration and an increased food production will both transgress the planetary boundary for consumptive freshwater use and worsen the already severe river depletion,” says lead author Malin Falkenmark.
The consequences would be a series of ecological collapses of riverine ecosystems, coastal ecosystems and lake ecosystems.
So what to do?
"Our study shows that synergies can be used to reduce the freshwater consumption through improved land use and changes in diets through less water intensive foods and reduced food losses. This way water can be freed up and used for sequestration,” co-author Louise Karlberg says.
However, it will not solve the main problem, namely too high emission levels.
"If humanity is to stay within the safe operating space for fresh water use (and climate change), climate change needs to be mitigated not only through carbon sequestration that relies on freshwater, but through decreased emission in the first place,” Karlberg says.
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