The correct answer is option 3: trapping of solar energy due to atmospheric carbon dioxide. The greenhouse effect is a natural process that occurs when certain gases in the Earth`s atmosphere, such as carbon dioxide, trap heat from the sun. These gases act like a "greenhouse," allowing sunlight to enter but preventing some of the heat from escaping back into space. This causes the temperature of the Earth to rise, leading to global warming. Option 1 is incorrect because the greenhouse effect is not related to pollution in houses in tropical regions. Option 2 is incorrect because atmospheric oxygen does not play a significant role in the greenhouse effect. Option 4 is incorrect because greenhouse cultivation is a different concept and not directly related to the greenhouse effect.