How much CO 2 at 1.5 °C and 2 °C?

The atmospheric concentration of CO2 at the time of passing 1.5 °C or 2 °C is unknown due to uncertainties in climate sensitivity and the concentrations of other GHGs. Impacts studies must account for a wide range of concentrations to avoid either over- or underestimating changes in crop yields and land and marine biodiversity.