1. Paris Agreement: The United States reentered the Paris Agreement on climate change in 2021. This international accord aims to limit global warming and reduce greenhouse gas emissions. The U.S. committed to reducing emissions by 50-52% below 2005 levels by 2030.

2. Renewable Energy: The adoption of renewable energy sources, such as solar and wind power, continued to grow in the United States. Many states established clean energy goals and implemented incentives for renewable energy projects.

3. Electric Vehicles (EVs): The promotion of electric vehicles and charging infrastructure became a priority. The Biden administration aimed to increase the number of EVs on American roads and reduce emissions from the transportation sector.

4. Carbon Pricing: Some states, like California, implemented cap-and-trade systems and carbon pricing mechanisms to reduce emissions from industries.

Environmental Regulations:

1. Clean Power Plan: The Clean Power Plan, introduced during the Obama administration, sought to reduce carbon emissions from power plants. The Trump administration rolled back these regulations, but the Biden administration signaled its intent to reinstate and strengthen them.

2. Fuel Efficiency Standards: The United States has periodically updated fuel efficiency standards for vehicles. The Biden administration proposed stricter standards to reduce emissions from the transportation sector.

3. Environmental Protection Agency (EPA): The EPA continued to be a key regulatory agency overseeing environmental policies and regulations in the U.S.

Effects on the United States:

1. Economic Impact: Environmental policies had both positive and negative economic impacts. While some argued that stricter regulations could harm certain industries, others saw opportunities in clean energy and green technologies.

2. Energy Transition: The transition to renewable energy sources and the reduction of coal power plants led to changes in the energy sector and employment patterns.

3. International Relations: The rejoining of the Paris Agreement signaled a renewed commitment to global climate action and improved diplomatic relations with other countries.

4. Resilience and Adaptation: As the U.S. faced more extreme weather events linked to climate change, there was a growing emphasis on resilience and adaptation strategies at the federal and state levels.