Can photosynthesis enable a global transition from fossil fuels to solar fuels, to mitigate climate change and fuel-supply limitations?

This review article considers Earth as an energy-storing (photosynthetic) and energy-consuming (metabolic) system. We evaluate whether and how photosynthetic, solar fuel-production systems can be engineered and deployed sufficiently rapidly to supplant enough fossil fuel supply to sustain a complex human economy and natural ecosystems over the long term. Geophysical, ecological, economic, technological and political constraints are quantified. We consider the potential to innovate and scale up promising systems such as microalgal and artificial photosynthetic systems to economic viability within a time frame meaningful for mitigating the effects of climate change and fuel-supply limitations. A future global society powered sustainably by solar fuels is forecast to require increased global photosynthetic productivity, through increased photon-conversion efficiency and production area. Increasing the efficiency of socioeconomic energy utilisation is also important. Meeting these challenges on the required time scale demands historically unprecedented technical progress, highlighting the need for both advanced international policy frameworks and scientific excellence. Based on evidence from a broad range of fields, a multiscale systems optimisation approach is identified as important, to integrate analyses from the scale of the global climate, economy and energy systems, down to the nanoscale of light-harvesting and carbon-fixing machinery that drives photosynthesis.