Quote from futurecurrents:
There are multiple lines of empirical evidence that increasing carbon dioxide causes an enhanced greenhouse effect. Laboratory tests show carbon dioxide absorbs longwave radiation. Satellite measurements confirm less longwave radiation is escaping to space at carbon dioxide absorptive wavelengths. Surface measurements find more longwave radiation returning back to Earth at these same wavelengths. The result of this energy imbalance is the accumulation of heat over the last 40 years.