Now that the US and Russia have pledged sizable reductions in their greenhouse gas emissions over the next 10–15 years, industrialized countries that spew 80% of the world’s pollutants have announced their commitments in advance of a new global agreement to slow climate change.

In its submission to the secretariat of the United Nations Framework Convention on Climate Change (UNFCCC) on 31 March, the Obama administration pledged to reduce US emissions of carbon dioxide and other greenhouse gases by 26–28% from 2005 levels by 2025. The next day, Russia promised to lower its emissions by 25–30% from 1990 levels by 2030. The UNFCCC is the parent treaty to the 1997 Kyoto Protocol and has 196 member states.

Neither China, the world’s largest greenhouse gas emitter, nor India, the third largest after the US, had submitted their pledges—so-called intended nationally determined contributions (INDCs)—by press time. But during President Obama’s November...

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