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Environmental Science Unit 7: Global change

Human activities are changing Earth's climate and ecosystems. Understanding the causes points to solutions.

Covers: Greenhouse effect, climate change causes and effects, ocean acidification, invasive species, endangered species, sustainability

Study guide

The greenhouse effect is natural: gases like carbon dioxide, methane, nitrous oxide and water vapor let sunlight in but absorb and re-radiate outgoing heat, keeping Earth warm enough for life. Human activities, mainly burning fossil fuels and deforestation, have raised atmospheric CO₂ well above preindustrial levels, strengthening the effect and warming the planet.

Climate change effects include rising average temperatures, melting glaciers and ice sheets, rising sea levels (from melting land ice and the expansion of warming water), more extreme weather such as heat waves, droughts and intense storms, shifting habitats and growing seasons, and threats to coastal communities and food supplies. Feedback loops, like melting ice reducing reflectivity, can speed warming. Solutions include renewable energy, efficiency, carbon pricing, reforestation and international agreements.

The oceans absorb much of the CO₂ we emit, which forms carbonic acid and lowers ocean pH. Ocean acidification makes it harder for corals, shellfish and plankton to build calcium carbonate shells and skeletons, threatening marine food webs. Warmer water also causes coral bleaching.

Invasive species are non-native species that spread rapidly, often because they lack natural predators. Examples include zebra mussels, kudzu and cane toads. They outcompete native species and disrupt ecosystems.

Endangered species face extinction from habitat loss (the biggest threat), invasive species, pollution, human population growth, climate change and overharvesting, summarized by the acronym HIPPCO. The Endangered Species Act and protected areas help, and wildlife corridors connect fragmented habitats.

Sustainability means meeting present needs without compromising future generations, through conservation, renewable resources and responsible consumption.

Methane traps far more heat per molecule than CO₂ (roughly 25–30 times as much over 100 years), though it stays in the atmosphere for only about a decade. Major human sources include livestock digestion, landfills, rice paddies and leaks from natural gas systems. Warming thaws Arctic permafrost, letting microbes decompose long-frozen organic matter and release CO₂ and methane. That causes more warming, so it's a positive feedback loop like melting sea ice.

Key ideas

• Greenhouse gases (CO₂, CH₄, N₂O, water vapor) trap heat.
• Burning fossil fuels and deforestation raise atmospheric CO₂.
• Effects: rising temperatures and sea levels, melting ice, more extreme weather.
• Oceans absorb CO₂ and become more acidic, harming shells and coral.
• Invasive species spread fast without natural predators.

Formulas and rules

Common mistakes

• Confusing the greenhouse effect (natural, needed) with enhanced warming from extra gases.
• Thinking ozone depletion is the main cause of climate change.

Words to know

Carbon dioxide (CO₂)

The main human-caused greenhouse gas.

Ocean acidification

Oceans absorbing CO₂, lowering pH.

Invasive species

Non-native species that spread fast without natural predators.

Sea-level rise

Caused by melting land ice and warming water expanding.

Greenhouse effect

Gases trapping outgoing heat in the atmosphere.

Greenhouse gases

CO₂, CH₄, N₂O and water vapor.

Climate change

Long-term shifts in temperature and weather patterns.

Methane (CH₄)

A potent greenhouse gas from agriculture, landfills and gas leaks.

Positive feedback (climate)

A change that speeds warming, like melting ice reducing reflectivity.

Coral bleaching

Corals expel algae under heat stress.

Endangered species

A species at risk of extinction.

HIPPCO

Habitat loss, Invasive species, Population growth, Pollution, Climate change, Overharvesting.

Endangered Species Act

U.S. law protecting threatened and endangered species.

Wildlife corridor

A strip of habitat connecting fragmented areas.

Sustainability

Meeting present needs without compromising future generations.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.