Sustainable Water Management Key to Scaling Up Bioenergy Production

Largely unmitigated global warming together with population growth would increase the number of people under water stress by about 80% in the simulations. Enhanced use of bioenergy with carbon capture and storage could limit climate change: When plants grow, they take up CO₂ from the air and build it into their trunks, twigs, and leaves. If this biomass is burned in power plants and the CO₂ is captured from the exhausts and stored underground (carbon capture and storage (CCS)), this can eventually help reduce the amount of greenhouse gases in our atmosphere – scientists call this ‘negative emissions’.

In many scenarios, these are seen as necessary for meeting ambitious climate mitigation targets if direct emission reductions proceed too slowly, and to balance any remaining greenhouse gas emissions that are difficult or impossible to reduce, for instance potentially in aviation, certain types of industry, or in livestock production.

Water Scarcity Remains a Huge Challenge
“According to existing scenarios, biomass plantations could increase by up to 6 million km² if global warming is to be limited to 1.5°C by the end of the century, the more ambitious of the two temperature targets of the Paris Agreement,” says coauthor Dieter Gerten from PIK. “We used these scenario inputs to run simulations in our high resolution global vegetation and water balance model to explore the freshwater implications. While substantial irrigation implied in a bioenergy plus CCS scenario including population growth suggests a 100% increase in the number of people facing water stress, combining it with sustainable water management brings the number down to 60%. This, of course, is still an increase, so challenging tradeoffs are on the table.”

Regions that already suffer from water stress today would be most affected in the climate change scenario, like the Mediterranean, the Middle East, northeastern China, South-East and southern West Africa. In the bioenergy plus CCS scenario without sustainable water management, high water stress extends to some otherwise unaffected regions, like eastern Brazil and large parts of Sub-Saharan Africa. Here, large biomass plantation areas in need of irrigation are assumed in the scenario analyzed. 

Sustainable Development Goals and Planetary Boundaries Must Be Taken into Account
Climate mitigation is one of the Sustainable Development Goals (SDGs) the world has agreed to achieve. The water–energy–environment nexus studied in this research highlights that pathways to sustainability must consider all affected SDGs.  

“The numbers show that either way, sustainable water management is a challenge to be addressed urgently,” says coauthor Wolfgang Lucht, head of PIK’s Earth System Analysis research department. “This new study confirms that measures currently considered to stabilize our climate, in this case bioenergy plus CCS, must take into account a number of further dimensions of our Earth system – water cycles are one of them. Risks and tradeoffs have to be carefully considered before launching large-scale policies that establish biomass markets and infrastructure. The concept of Planetary Boundaries considers the whole Earth system, including but not limited to climate. Particularly the integrity of our biosphere must be acknowledged to protect a safe operating space for humanity.”