Earth’s dynamic systems are sustained by continuous exchanges of elements, known as cycles of matter. These fundamental processes involve the movement and transformation of chemical substances between living organisms and the non-living components of the planet, such as the atmosphere, oceans, and land. These cycles ensure the availability of essential elements necessary for all life forms to thrive.
Natural Cycles of Matter
Cycles of matter describe the pathways chemical elements follow as they move through different reservoirs on Earth, including the atmosphere, oceans, land, and living organisms. For instance, the carbon cycle involves carbon moving between these compartments through photosynthesis and respiration. Water continuously circulates through evaporation, condensation, and precipitation, residing in oceans, glaciers, and groundwater. Nitrogen cycles between the atmosphere, soil, and living organisms, with the atmosphere holding the largest reservoir of nitrogen gas. These natural cycles maintain a delicate balance, ensuring elements are available for life to persist.
Altering the Carbon Cycle
Human activities significantly influence these natural cycles, particularly the carbon cycle. A primary driver is the extensive burning of fossil fuels like coal, oil, and natural gas. These fuels formed over millions of years from ancient organic matter that stored carbon underground. When combusted for energy, this stored carbon is rapidly released into the atmosphere as carbon dioxide (CO2), a process thousands of times faster than its natural burial. Atmospheric CO2 levels are now approximately 50 percent higher than before the Industrial Revolution, with global fossil fuel emissions reaching an estimated 37.4 billion tons in 2024.
Deforestation and changes in land use also contribute to altering the carbon cycle. Forests act as significant carbon sinks, absorbing carbon dioxide from the atmosphere and storing it in their biomass and soils. When forests are cleared, especially through burning, this stored carbon is released back into the atmosphere. This also reduces the planet’s capacity to absorb CO2. In 2023, the global loss of tropical forests alone released roughly six percent of estimated global carbon dioxide emissions. While natural processes like plant growth and ocean absorption remove about half of human-emitted carbon dioxide, the remaining portion accumulates in the atmosphere, disrupting the cycle’s natural balance.
Global Repercussions
The human-induced increase of carbon dioxide in the atmosphere leads to global repercussions, primarily through climate change and ocean acidification. Elevated atmospheric CO2 concentrations intensify the natural greenhouse effect, causing the planet to retain more heat. This leads to a rise in global average temperatures, which have increased by approximately 1.3°C since pre-industrial times. Such warming contributes to altered weather patterns, more frequent extreme weather events, and the melting of ice, with atmospheric CO2 levels now higher than at any point in at least 3 million years.
A significant portion of excess atmospheric carbon dioxide is absorbed by the oceans. When CO2 dissolves in seawater, it forms carbonic acid, releasing hydrogen ions and increasing the ocean’s acidity and lowering its pH. Since the Industrial Revolution, the ocean’s surface pH has dropped from 8.21 to 8.10, making it about 30 percent more acidic. This change makes it more challenging for many marine organisms, particularly those that build shells or skeletons from calcium carbonate, to form and maintain their structures. The increased acidity can also impair the development and survival of sensitive larval stages, potentially disrupting marine food webs and ecosystems.