First paragraph by the United States’ National Oceanic and Atmospheric Administration:
Yes, it matters. Observed and anticipated increases in greenhouse gas emissions from China and other countries don’t let Americans off the hook for reducing emissions. From a purely physical perspective, any reduction in emissions helps minimize future temperature increases. From the perspective of fairness, the United States has released more heat-trapping gases to date than either China or India, the world’s two most populous countries. Carbon dioxide is a long-lived greenhouse gas that can linger in Earth’s atmosphere for thousands of years. Consequently, the United States bears more responsibility for the amount of warming that has occurred so far and will persist for millennia.
