In a speech that compared the danger of environmental degradation to the threat of terrorism, British Prime Minister Tony Blair yesterday outlined a sweeping plan to combat global warming. Blair called on his country, the European Union, and would-be E.U. members in Eastern Europe to cut carbon dioxide emissions 60 percent by 2050. That figure, which radically exceeds the one in the Kyoto Protocol on climate change, is the one scientists say could save the planet from the most dire consequences of the greenhouse effect. In his speech, Blair also criticized President Bush for backing out of Kyoto and failing to propose a meaningful alternative, and he promised to maintain pressure on the U.S. and other industrialized nations to cut emissions. Environmentalists praised the prime minister’s vision, but also said it was long on rhetoric and short on concrete policy proposals.