Read this excerpt from "A Student's Guide to Global Climate Change."

Climate change will lead to more hot days and more heat waves. As a result, people will need to use more air conditioning to stay cool. As people use more air conditioning, electricity shortages and blackouts could increase. Because most electricity is currently produced by burning fossil fuels, using more electricity to run air conditioners will also add more greenhouse gases to the atmosphere.

What problem does the excerpt present?

There will be more hot days and heat waves in the future.
People will need air conditioning more often in the future.
Power shortages and blackouts may increase.
Greenhouse gases are being added to the environment.