Dr. Tim Newfield, Princeton University.
The June 1991 Pinatubo eruption in the Philippines was one of the largest volcanic eruptions of the twentieth century. It is well documented. There are living witnesses, newspaper articles, detailed surveys of the mountain before and after it blew its top, and satellite maps of the ejecta. The eruption was photographed from the ground and the air, and today you can even YouTube it. Pinatubo released up to 20 megatons of sulphur dioxide as many as 35 kilometers into the sky. It turned into fine sulphuric acid aerosol, and, within weeks, enveloped much of the Earth. The aerosols were suspended in the atmosphere for around two years. While there, they "veiled" the sun by absorbing or "backscattering" solar radiation. That heated the stratosphere but cooled Earth's surface. Read more