Explain why scientists are concerned about human activities that cause global warming if global warming is caused by the greenhouse effect and the greenhouse effect is a natural part of Earth’s climate.

Answer:

The natural greenhouse effect keeps Earth warm enough for life, but human activities such as burning fossil fuels and deforestation add extra greenhouse gases to the atmosphere. This strengthens the effect and causes temperatures to rise more rapidly than they would from natural processes alone, increasing the risk of disruptive changes to ecosystems and human societies.