Changement climatique - Recherche française (avec laboratoires CNRS) - 2010-2015

Many future energy and emission scenarios envisage an increase of bioenergy in the global primary energy mix(1-4). In most climate impact assessment models and policies, bioenergy systems are assumed to be carbon neutral, thus ignoring the time lag between CO2 emissions from biomass combustion and CO2 uptake by vegetation(5). Here, we show that the temperature peak caused by CO2 emissions from bioenergy is proportional to the maximum rate at which emissions occur and is almost insensitive to cumulative emissions. Whereas the carbon-climate response (CCR; ref. 6) to fossil fuel emissions is approximately constant, the CCR to bioenergy emissions depends on time, biomass turnover times, and emission scenarios. The linearity between temperature peak and bioenergy CO2 emission rates resembles the characteristic of the temperature response to short-lived climate forcers. As for the latter(7-9), the timing of CO2 emissions from bioenergy matters. Under the international agreement to limit global warming to 2 degrees C by 2100(3), early emissions from bioenergy thus have smaller contributions on the targeted temperature than emissions postponed later into the future, especially when bioenergy is sourced from biomass with medium(50-60 years) or long turnover times (100 years).