The correct answer is: A. Increase in CO2.
The greenhouse effect is a natural process that warms the Earth’s surface. It is caused by greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, which trap energy in the atmosphere. These gases allow sunlight to pass through the atmosphere and reach the Earth’s surface, but they absorb some of the heat that is reflected back from the surface. This trapped heat warms the atmosphere and the Earth’s surface.
The greenhouse effect is essential for life on Earth. Without it, the Earth’s average temperature would be about 60 degrees Fahrenheit colder, and life as we know it would not be possible. However, human activities are increasing the amount of greenhouse gases in the atmosphere, which is causing the greenhouse effect to become stronger. This is leading to global warming, which is causing a number of changes to the Earth’s climate, including rising sea levels, more extreme weather events, and changes in plant and animal life.
Option B is incorrect because an increase in oxygen would not cause the greenhouse effect. Oxygen is a greenhouse gas, but it is not a major contributor to the greenhouse effect. The main greenhouse gases are carbon dioxide, methane, and nitrous oxide.
Option C is incorrect because a decrease in oxygen would not cause the greenhouse effect. Oxygen is a greenhouse gas, but it is not a major contributor to the greenhouse effect. The main greenhouse gases are carbon dioxide, methane, and nitrous oxide.
Option D is incorrect because a decrease in carbon dioxide would not cause the greenhouse effect. Carbon dioxide is the main greenhouse gas that is causing global warming.