Final answer:
The saw-toothed pattern of CO₂ fluctuations at Mauna Loa is due to the seasonal cycle of plant photosynthesis and decay. Superimposed on this natural cycle is a continuous increase in CO₂ levels caused by human activities such as the burning of fossil fuels.
Step-by-step explanation:
The saw-toothed, up-and-down fluctuations of CO₂ levels recorded at Mauna Loa, Hawaii, from 1960 to 1995 are predominantly attributed to the seasonal cycle of photosynthesis. During spring and summer in the northern hemisphere, plants absorb more CO₂ for photosynthesis, leading to a decrease in atmospheric CO₂ levels. In contrast, during the autumn and winter months, when vegetation dies and decays, the process of respiration and decay releases CO₂ back into the atmosphere, causing levels to rise again. This natural, annual fluctuation sits atop a general upward trend in CO₂ concentrations, which is primarily driven by the burning of fossil fuels and industrial activities related to human activity.
Historically, atmospheric CO₂ fluctuated between 180 ppm (parts per million) and 300 ppm over 50,000-year cycles. However, recent data show an unprecedented rise in CO₂ levels, surpassing the historical maximum of 300 ppm due to human-induced emissions. This increase, starting with the Industrial Revolution, has raised levels from around 280 ppm in preindustrial times to over 400 ppm today. Consequently, this sudden and dramatic increase over a matter of hundreds of years, rather than thousands, is altering our climate at a rapid pace.