"What impact can a very large volcanic eruption have on earth's climate?" 1. It will warm the earth's surface as more lava is released by the volcanic eruption. 2. It will cool the earth's surface as more snow will fall with the presence of more condensation nuclei. 3. It will warm the earth's surface as more heat is trapped by the dust particles. 4. It will cool the earth's surface as radiation from the sun is blocked from entering the atmosphere.

The impact of a very large volcanic eruption that have an effect on earth's climate is It will cool the earth's surface as radiation from the sun is blocked from entering the atmosphere.

Explanation:

A very large volcanic eruption will spew tonnes of fine dust particles (pyroclast) into the atmosphere. These particles will be spread over large area by wind and the particles will remain suspended in the air for longer periods before they settle on the earth's surface.

The suspended particles will block the sun, and by reflecting most of the sunlight before it reaches the earth’s surface, will cause the surface temperatures to drop.  

This same phenomenon caused the demise of dinosaurs after a meteorite strike threw dust particles into the atmosphere that lingered for a long time smothering plant life too.