The primary factor contributing to the greenhouse effect is the accumulation of greenhouse gases in the Earth's atmosphere. Key gases include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases trap heat from the sun, preventing it from escaping back into space, which leads to an increase in global temperatures. This effect is essential for maintaining the Earth's climate; however, human activities, such as burning fossil fuels and deforestation, have significantly increased the concentration of these gases, exacerbating climate change and altering weather patterns.