Modern day volcanoes, i.e. the last few thousand years seem to be responsible for noticable cooling effects on the climate, i.e. Mount Pinatoba, Tambora etc.  This is i assume is down to dust, ash and sulphur dioxide been spewed into the air and reflecting incoming solar radiation.

 Although it seems volcanism in earths geological history appear to be responsible for notable warming events, attributed to greenhouse gas emmisions.  I know the residence time of greenhouse gasses are usualy longer than ash, dust and sulphur aerosols, however continued eruptions i would imagine would keep a constant supply of sulphur in the atmosphere thus cooling the planet.

Please explain this contradiction.

Thanks

Mark