Can it turn down the heat? The Paris Agreement to combat global warming goes into effect Friday, thanks to the efforts of 197 nations aimed at cutting greenhouse gas emissions. The 55 countries that generate more than half of the world’s carbon emissions combined have already ratified the deal. Signatories agree to pursue reductions aimed at lowering global temperatures to 2.7 degrees Fahrenheit above pre-industrial levels. While advocates say it opens up green business opportunities, U.S. presidential hopeful Donald Trump has promised, if elected, to scuttle the plan.