LCA has been extensively used in the last few years and a large number of studies have been published in the literature. These studies show a great variability in results of comparable systems. It somehow leads policy-makers to consider the LCA approach as an inconclusive method. Some attempts have been developed to assess LCA results variability; however, they remain mostly qualitative. In this paper, a method based on Global Sensitivity Analysis (GSA) is presented in order to understand the origin of results variability. A general variance decomposition based on the Sobol indices is applied to quantify the influence of input parameters on the environmental answer. A preliminary study is done by using this GSA on a large set of integrated photovoltaic systems greenhouse gas (GHG) performances. We identify that the irradiation parameter has the biggest influence on those GHG performances. The other parameters such as lifetime or performance ratio have been identified as having a smaller but significant influence on the GHG results variability. The GHG performances range from 24 to 230 g CO2eq/kWh with 75% of the performance ranging from 23.8 to 93.5g CO2eq/kWh.