What are the impact of human activities on environmental issues?

The human activities will create externalities, both negative and positive. It will increase marginal social cost more than marginal social benefits. This will cause an overproduction and the overuse of resources. For example, the air pollution caused by overproduction because the producer does not need to pay the cost to clean it. 

Only local.

L.A. SMOG fixed.

Pittsburgh industry, fixed.

London "fog". fixed.

Similar to certain areas in Brazil, China, India, Asian Pacific Islands. etc.

Not to fret it.  When Biden "resigns" the Paris Accords.

The Accords make it possible for everybody to feel good.

The China, India, et al signers merely agree to ... at sometime in the future, when they feel like doing something they might do it.  Meanwhile the U.S.A. becomes liable to reduce pollution for 3% to less. And, maybe pay for pollution controls in other countries.