1. Of the following, which is believed to be the largest source of the increased concentration of carbon dioxide in Earth's atmosphere during the last hundred years?
Answer: B
Combustion of coal and other fossil fuels
The largest source of the increased concentration of carbon dioxide in Earth's atmosphere over the last hundred years is attributed to the combustion of coal and other fossil fuels. This process releases significant amounts of carbon dioxide as a byproduct, contributing substantially to atmospheric greenhouse gas levels.
A) Increased volcanic activity
Increased volcanic activity does release carbon dioxide, but its contribution to the overall atmospheric concentration is relatively minor compared to human activities. Volcanic eruptions typically occur sporadically and do not account for the consistent and large-scale CO2 emissions observed in recent history.
B) Combustion of coal and other fossil fuels
This option is correct as the burning of coal, oil, and natural gas for energy and transportation has significantly increased carbon dioxide levels in the atmosphere. These fossil fuel sources are responsible for the majority of anthropogenic CO2 emissions, particularly in industrialized nations.
C) Decreased photosynthetic activity of plants
While decreased photosynthetic activity can contribute to higher CO2 levels by reducing the amount of carbon dioxide absorbed from the atmosphere, this factor is not the primary driver of the significant increase in CO2 concentrations over the last century. Human activities, particularly fossil fuel combustion, far outweigh this effect.
D) Increased human respiration due to increases in the human population
Increased human respiration does contribute to carbon dioxide emissions, but it is relatively negligible compared to emissions from fossil fuel combustion. The scale of emissions from human respiration does not match the vast quantities of CO2 released by burning fossil fuels.
Conclusion
The combustion of coal and other fossil fuels is the predominant source of the rise in atmospheric carbon dioxide over the past century, far exceeding any contributions from volcanic activity, decreased photosynthesis, or increased human respiration. This underscores the impact of industrialization and energy consumption on climate change and highlights the urgent need for sustainable energy practices.