You probably know that trees extract carbon dioxide from air. Therefore, it follows that the large scale cutting down of forests upsets the delicate balance of gases in the atmosphere. In 1938, British physicist G.S.Callender determined that higher levels of carbon dioxide caused warmer temperatures in America and Europe. He produced data from ice cores showing that levels of carbon dioxide in the atmosphere had been raising since the industrial age began. Callender believed greenhouse warming was on its way, but no one can particularly worried at that time. Callender's work attracted some attention, and climatology textbooks of the 1940's and 1950's routinely included a brief reference to his studies. But most meteorologist did not give much importance to Callender's ideas.
While Callender couldn't prove that greenhouse effect warming was underway, he had given sound reasons to reconsider the question. We owe much to his courage. His claims rescued the idea of global warming from obscurity. Moreover, not everyone dismissed his claims. His ideas attracted scientific curiosity, and attracted new thoughts on the subject.
