The Unites States is the second-most polluting country in the world, so pulling out of the Paris Agreement will affect climate change significantly. The US is second only to China for pollution, supplying 14.34% of the world's CO2 emissions, according to Wikipedia. So the US's withdrawl from the Paris Agreement will impact climate change greatly, and it slows the progress that the world is beginning to make on the climate change front. Hopefully the states who have taken up the mantel of maintaining the Paris Agreement will help the US in reducing its CO2 emissions.