Final answer:
The Mauna Loa data show annual CO2 fluctuations due to photosynthesis and a steady year-by-year increase due to fossil fuel combustion. The Keeling Curve represents this trend, with CO2 levels now well above historical natural variations, indicating a significant human influence on climate change.
Step-by-step explanation:
The Mauna Loa data show an annual variation in CO2 levels due to the seasonal cycle of photosynthesis, where plants absorb CO2 during the growing season and release it when they decay and decompose, leading to lower levels in the summer and higher levels in the winter. Beyond this seasonal cycle, a steady year-by-year increase in atmospheric CO2 concentration has been observed, primarily due to the burning of fossil fuels. This pattern is reflected in the "Keeling Curve". Pre-industrial atmospheric CO2 concentrations were around 280 ppm, but recent measurements show levels have risen significantly, breaching the historical maximum of 300 ppm and reaching over 400 ppm.
Figure 9.1 illustrates this relentless upward trend, which is accelerating at about 2.6 ppm per year. This increase correlates with a global average temperature rise of approximately 1℃ over the same period. Prior to the Industrial Revolution, natural factors like the Milankovitch cycles influenced climate change over tens of thousands of years, but the current rapid escalation in CO2 levels and associated climate change is driven predominantly by human industrial activities.