Problem: In the early and mid-20th century, developed countries were so heavily polluted that the world was warming slowly. "This was the era of the London fogs and of very extreme pollution in the U.S.," said Gabi Hegerl, a climatologist at the University of Edinburgh. A recent study in the Journal of Advances in Modeling Earth Systems, for instance, found that in the 1980s these particles offset approximately 80 percent of climate warming. Agree or disagree