This paper quantifies the probable impacts of ionospheric scintillation on the proposed European Space Agency BIOMASS synthetic aperture radar (SAR). BIOMASS is a 435 MHz quad-polarised.SAR in a dawn-dusk orbit, with a primary objective of measuring woody biomass density and tree heights with near-global coverage. The climatological model WBMOD is used to generate multiple random ionospheric phase screens, from which are derived SAR impulse response functions (IRFs) for a range of locations, times and solar and geomagnetic activity levels. The statistics of IRF degradation are presented in terms of the integrated and peak sidelobe ratios, resolution increases, azimuthal shifts and reductions of the main lobe peak. The ionospheric impacts for global forest regions are found to be negligible under all conditions except at high latitudes in the North American sector under high solar and geomagnetic activity. Consequences for ice monitoring (at higher latitudes) will be much more widespread.