Biochar is the carbon-rich organic matter that remains after heating biomass under minimization of oxygen during a process called pyrolysis. Its relevance to deforestation, agricultural resilience, and energy production, particularly in developing countries, makes it an important issue. This report offers a review of what is known about opportunities and risks of biochar systems. Its aim is to provide a state of the art overview of current knowledge regarding biochar science. In that sense the report also offers a reconciling view on different scientific opinions about biochar providing an...