Carbon dioxide and methane are greenhouse gases. When their levels increase, more infrared radiation is absorbed and re-emitted, so the average global temperature rises. This is global warming, and it causes climate change. Possible effects include melting polar ice and glaciers, and rising sea levels, which cause flooding of low-lying land. Weather may become more extreme, with more storms, droughts and heatwaves. Changes in rainfall patterns can affect crop growth and food supply, and habitats may change so that some species cannot survive.
These effects may be reduced, or mitigated, by cutting the amount of greenhouse gases released and by removing some from the air. Using renewable energy such as wind and solar, or nuclear power, means burning less fossil fuel. Energy efficiency and public transport also reduce emissions. Carbon capture and storage traps carbon dioxide from power stations and stores it underground. Planting trees removes carbon dioxide by photosynthesis, and capturing methane from landfill sites reduces methane emissions.
Each option has limits. Some are expensive, some technologies are not yet fully developed, and many need international agreement and changes to how people live. The scale of the problem is global and the risks are uncertain, so decisions have to balance the risks against the costs.