Some human activities increase the amounts of carbon dioxide and methane in the atmosphere. You need to recall two activities for each gas.
Carbon dioxide is released when fossil fuels are burned, for example in power stations, in car engines and for heating homes. It is also released when forests are cut down and burned, because there are fewer trees to take in carbon dioxide by photosynthesis. This is called deforestation.
Methane is released by farming. Cattle and other livestock produce methane in their digestion, and rice paddy fields produce it as microbes break down plant material. Methane is also released from rubbish in landfill sites as waste rots.
Many scientists believe that these activities will cause the temperature of the Earth's atmosphere to rise at the surface, leading to global climate change. This view is based on peer-reviewed evidence, where other scientists check the methods and conclusions before the results are published. Climate is a very complex system, so it is hard to model. Models are simplified, and some reports in the media may use only part of the evidence and may be biased.