Final answer:
CO2 levels rise and oxygen levels decrease due to the combustion of fossil fuels, which creates a unique chemical signature. The highest CO2 levels in the last 800,000 years coincide with industrialization, supporting human contributions to rising greenhouse gases and the resulting climate change.
Step-by-step explanation:
The evidence that the increase in carbon dioxide (CO2) is due to fossil fuel combustion includes that oxygen levels in the atmosphere are slightly decreasing. This is significant because the process of burning fossil fuels involves combining carbon (from the fuel) with oxygen (from the air) to produce CO2, which consequently depletes atmospheric oxygen. A steady decrease in oxygen, alongside a dramatic increase in CO2, provides a clear chemical signature of fossil fuel combustion. Reliable data from ice cores show that the concentration of CO2 is at its highest in the last 800,000 years, and possibly in the last 20 million years. Furthermore, atmospheric CO2 levels have risen from preindustrial levels of approximately 280 parts per million (ppm) to more than 400 ppm today.
This increase in CO2 is causing a greenhouse effect that is resulting in climate change and impacting global biodiversity. Measures of the isotopic signatures also support that this added CO2 is largely due to burning fossil fuels. The decrease in oxygen, paired with the rise in CO2 levels, underscores the broader shift in the carbon cycle and necessitates a transition away from fossil fuels to alternative energy sources to mitigate the negative effects of climate change.