A small but vocal number of people maintain that the observed temperature anomalies are not the result of greenhouse gas emissions from human activities warming the planet. (bbc.com)
Consequently an increase in the atmospheric concentration of greenhouse gases from human activities such as burning fossil fuels leads to an enhanced greenhouse effect. (newstatesman.com)
Some greenhouse gases occur naturally in the atmosphere, while others result from human activities such as burning of fossil fuels such as coal. (sciencedaily.com)