Clouds affect the Earth's climate in ways that depend on the type of cloud (solid/liquid water). From observations at Concordia (Antarctica), we show that in supercooled liquid water (liquid water for temperatures below 0°C) clouds (SLWCs), temperature and SLWC radiative forcing increase with liquid water (up to 70 W m⁻²). We extrapolated that the maximum SLWC radiative forcing can reach 40 W m⁻² over the Antarctic Peninsula, highlighting the importance of SLWCs for global climate prediction.