Final answer:
The CO₂ concentration at Mauna Loa reaches its lowest point in October annually due to reduced photosynthesis in the fall, as evidenced by the Keeling Curve. The data also reveals a continuous increase in CO₂ levels, linked to human activities like fossil fuel burning. Ice core records support findings of historically unprecedented CO₂ concentrations.
Step-by-step explanation:
The CO₂ concentration at Mauna Loa reaches its lowest value in October each year primarily due to the seasonal cycle of photosynthesis. During the spring and summer months in the Northern Hemisphere, plants absorb a significant amount of CO₂ from the atmosphere for photosynthesis, which lowers the atmospheric concentration. As autumn arrives and photosynthesis decreases because of plant senescence and decreased sunlight, the CO₂ levels begin to rise again, reaching their lowest point in October before the winter slowdown in plant activity.
The data collected at Mauna Loa since 1958, often referred to as the “Keeling Curve”, shows not only these seasonal fluctuations but also a relentless year-by-year increase in CO₂ levels, currently at about 2.6 ppm per year. This long-term increase is largely attributed to human activities, especially the burning of fossil fuels which contributes to about three-quarters of the increased atmospheric CO₂ levels.
Furthermore, records from ice core data indicate that the current concentration of CO₂ in the atmosphere is the highest in the last 800,000 years, and possibly the last 20 million years. Hence, while there is a natural seasonal pattern observed in CO₂ fluctuations, the overarching trend is an increase stemming from anthropogenic causes.