Final answer:
The last 200,000 years have seen a dramatic increase in atmospheric carbon dioxide and methane levels beyond natural historical cycles, predominantly due to human activities such as burning fossil fuels and deforestation.
Step-by-step explanation:
Throughout the last 200,000 years, the Earth's atmosphere has experienced shifts in its composition. A significant change is the increase in carbon dioxide levels, which have risen from a historical cycling pattern of 180 to 300 parts per million (ppm) to levels beyond 300 ppm. Evidence from ice cores, tree rings, and other geological data indicates that before industrialization, changes in these levels correlated with natural phenomena such as Milankovitch cycles, volcanic activity, and variations in solar radiation.
However, the rapid increase in carbon dioxide levels during recent centuries is a direct result of human activities, particularly the burning of fossil fuels, deforestation, and industrial processes. Concurrently, there has been a significant increase in methane levels due mainly to anaerobic decomposition in landfills, melting clathrates in the ocean, and livestock farming. These increases in greenhouse gases contribute to the overarching trend of global climate change and are expected to affect biodiversity significantly.