Volcanic flood basalt eruptions have been linked to or are contemporaneous with major climate disruptions, ocean anoxic events, and mass extinctions throughout at least the last 400M years of Earth’s history. Previous studies and recent history have shown that volcanically-driven climate cooling can occur through reflection of sunlight by H₂SO₄ aerosols, while longer-term climate warming can occur via CO₂ emissions. We use the Goddard Earth Observing System Chemistry-Climate Model to simulate a four-year duration volcanic SO₂ emission of the scale of the Wapshilla Ridge member of the Columbia River Basalt eruption. Brief cooling from H₂SO₄ aerosols is outweighed by dynamically and radiatively driven warming of the climate through a three orders of magnitude increase in stratospheric H₂O vapor.