Earth as a System: Energy, Matter, and Life · Lesson 12 of 13
Human Impact on Earth’s Processes
“One shortcut in one sphere can send an invoice to every other sphere.”
• Explain how fuel use and deforestation alter carbon and oxygen cycles. • Describe ocean acidification as a consequence of added carbon dioxide. • Explain eutrophication step by step. • Trace the cross-sphere effects of deforestation. • Explain the formation and effects of photochemical smog. • Identify actions that reduce pressure on Earth-system processes.
A forest cleared for land, fuel burned in a city and fertiliser washed from a field appear to be separate actions. In an interconnected system, each can alter several processes at once. The important question is not only what changes first, but how that change travels through air, water, soil and living communities.
Burning coal, petroleum and natural gas releases carbon dioxide and other pollutants. Deforestation releases stored carbon when vegetation burns or decays and also removes plants that could absorb carbon dioxide. Together these activities strengthen atmospheric warming and alter the carbon-oxygen balance.
Ocean acidification is the decrease in ocean pH caused mainly by the absorption of additional atmospheric carbon dioxide.
Dissolved carbon dioxide reacts with water and changes the balance of carbonate compounds. This can reduce the carbonate available to organisms that build shells or skeletons. Plankton, shell-forming organisms and coral communities may be affected, and the effects can spread through marine food webs. Warmer water can also hold less dissolved gas and may change ocean uptake.
Problem
Trace one possible chain of effects.
- 1.Fuel combustion adds carbon dioxide to the atmosphere.
- 2.Some of the added gas dissolves in seawater.
- 3.Chemical changes lower pH and alter carbonate availability.
- 4.Shell-building organisms must spend more energy maintaining structures.
- 5.Food webs and reef habitats can be affected.
Eutrophication is the excessive enrichment of water with nutrients, causing dense growth of algae and a later decline in dissolved oxygen.
Problem
Explain why a nutrient-rich lake can lose fish.
- 1.Runoff carries nitrate and phosphate compounds into the lake.
- 2.Algae grow rapidly and form a bloom.
- 3.Algae and shaded aquatic plants die in large amounts.
- 4.Decomposers use oxygen while breaking down the dead matter.
- 5.Dissolved oxygen falls, causing fish and other animals to suffocate.
| Sphere | Possible consequence of large-scale forest removal |
|---|---|
| Biosphere | Habitat loss, reduced biodiversity and disrupted food webs |
| Atmosphere | Less carbon dioxide uptake and less transpiration |
| Hydrosphere | Faster runoff and altered stream flow |
| Geosphere | Greater erosion and loss of fertile soil |
| Cryosphere and climate links | Warming can indirectly influence snow and ice stores |
Roots bind soil and create channels for infiltration. Leaves intercept rain, while transpiration returns water vapour to the atmosphere. Removing trees can therefore increase runoff and erosion, decrease local moisture recycling, reduce carbon storage and eliminate habitat. A cross-sphere explanation is more complete than saying only that fewer trees remain.
What if ...
If photosynthesis stopped globally, new food production at the base of most food webs would cease. Oxygen production would fall, while respiration, decay and combustion would continue consuming oxygen for some time. Carbon dioxide would accumulate and ecosystems would collapse. The thought experiment reveals how strongly energy capture, food webs and gas cycles depend on photosynthetic organisms.
Threads of Curiosity
Vehicle emissions release nitrogen oxides and other reactive substances. In sunlight they can form photochemical smog containing harmful ground-level ozone. This ozone can irritate lungs and damage leaves. It must be distinguished from stratospheric ozone, which protects life from ultraviolet radiation.
Mission LiFE
Mission LiFE, introduced internationally in 2021, encourages mindful lifestyles that conserve resources. Actions such as saving electricity and water, using public transport, reducing waste, repairing and reusing products, protecting vegetation and choosing renewable energy reduce pressure on several cycles. Individual action becomes more effective when supported by thoughtful design, community cooperation and sound public systems.
Pause and Ponder
International agreements can address problems that cross borders. The Montreal Protocol reduced ozone-depleting substances and began the recovery of the ozone layer. The Kyoto Protocol and Paris Agreement seek reductions in greenhouse-gas emissions, although progress is more difficult because energy, transport, industry and land use are deeply connected with daily life and development.
Human activities usually create a chain of direct and indirect effects. State the action, changed process, affected reservoir or sphere, and later biological or physical consequence.
Quiz
Which description best matches Ocean Acidification?
Which description best matches Eutrophication?
Which term matches this description: Ocean acidification is the decrease in ocean pH caused mainly by the absorption of additional atmospheric carbon dioxide.
Which term matches this description: Eutrophication is the excessive enrichment of water with nutrients, causing dense growth of algae and a later decline in dissolved oxygen.
Which statement is a key takeaway from this lesson?
Practice Problems
- Trace fuel combustion through atmosphere, ocean and biosphere.
- Explain every stage of eutrophication in order.
- Describe four sphere-level effects of deforestation.
- Distinguish smog ozone from protective ozone.
- Explain why personal choices and collective systems must work together.
Key Takeaways
• Human activities can speed up transfers that were naturally slow. • Added carbon dioxide affects atmosphere, ocean and life. • Excess nutrients can remove dissolved oxygen from water. • Deforestation changes carbon, water, soil and habitats together. • Coordinated action can reduce and sometimes reverse damage.