"Global warming did level off between 1940 and 1975. We now know that this was largely a result of dust and aerosols sent by humans into the atmosphere that temporarily overwhelmed the warming effect from greenhouse gases. In the 1970s, it was not yet clear whether the cooling effect from aerosols would be greater than the heating produced from greenhouse gases. "
Whenever I hear someone talk about human activity "causing" global warming, I have to wonder if they've ever seen the eruption of Mount St. Helens which spewed thousands of tons of debris, noxious chemicals and gases into the atmosphere. Over time, mother nature managed to 'scrub' it all out of the air. These are the events which have an impact on climate change and they occur all over the world on a fairly regular basis.
The depth of ignorance of some people knows no limit.....
Since I've always been interested in volcanoes, I have a decent layman's knowledge of them. Volcanoes actually produce very little carbon dioxide, which is most well-known greenhouse gas of concern. Volcanoes produce significantly more sulfur dioxide and ash (depending on the type of volcano; Hawaiian-type volcanoes don't produce much ash). The strength of the eruption will determine how much gets into the stratosphere and affects climate. The 1980 St. Helens blast was quite lateral and also not that big, so very little eruptive products made it to the upper atmosphere. For El Chichon in 1983 and Pinatubo in 1991, the eruptions were virtually vertical and powerful, and the atmospheric effects were prolonged (in the case of Pinatubo, for about two years). El Chichon also had the distinction of being one of the most sulfur-rich eruptions ever observed.
The ash doesn't stay in the atmosphere nearly as long, of course.