Final answer:
Human activity significantly increases atmospheric CO2 levels by burning fossil fuels, deforestation, and intensive farming, which disrupts the carbon cycle and amplifies the greenhouse effect, contributing to global warming.
Step-by-step explanation:
Human activities affect the carbon cycle by increasing atmospheric CO2 levels. The burning of fossil fuels such as coal and petroleum since the Industrial Revolution has dramatically released carbon into the atmosphere. This process alters the natural balance of carbon exchange, increases greenhouse gases, and contributes to global climate change. Deforestation further exacerbates this issue by reducing the number of trees that can absorb CO2 for photosynthesis. Activities like agriculture and animal husbandry also contribute to increased CO2 and methane levels, affecting the carbon cycle and escalating the greenhouse effect.
On a global scale, the increased CO2 in the atmosphere from human activities results in changes to climate and weather patterns. The greenhouse effect, while a natural and necessary phenomenon, is intensified by the elevated levels of greenhouse gases due to human actions, trapping more heat and leading to global warming.