The U.S. and <a href="https://en.wikipedia.org/wiki/China" id="mwAXg" rel="mw:WikiLink" title="China">China</a>, together responsible for <a href="https://en.wikipedia.org/wiki/List_of_countries_by_greenhouse_gas_emissions" id="mwAXk" rel="mw:WikiLink" title="List of countries by greenhouse gas emissions">40% of the world's carbon emissions</a>, both formally ratify the <a href="https://en.wikipedia.org/wiki/Paris_Agreement" id="mwAXo" rel="mw:WikiLink" title="Paris Agreement">Paris global climate agreement</a>.