In the summer of 1988, much of the United States was gripped by drought and heat. On June 23, NASA climate scientist James Hansen appeared before the Senate Committee on Energy and Natural Resources and said plainly that the greenhouse effect was no longer only a theory about the future — it had been detected.
He told the committee that he was highly confident the warming measured in the 1980s was not a natural swing but the result of gases people had added to the atmosphere. The room was hot, and the day outside was hotter; the setting made the testimony hard to ignore.
Coming six years after the Arrhenius notice above, this hearing marks the moment the question moved out of scientific journals and into government, and from government into public argument — where it has stayed ever since.
For your classroom
Why it still matters in a classroom: the same scientific conclusion sat in a Swedish chemist's notebook in 1896 and in an American newspaper column in 1902. What changed in 1988 was not the science but the audience — an argument about what to do about it.