Global Change and Climate in the Earth System — Causes, Cycles, and Human Impact | Chapter 23 from Earth: Portrait of a Planet

How do global forces shape our planet’s past, present, and future? Chapter 23 of Earth: Portrait of a Planet by Stephen Marshak explores the profound topic of global change, tracing both natural cycles and the accelerating effects of human activity. For a concise audio-visual summary, watch the chapter video on YouTube, or read below for a complete guide to the science behind Earth system transformation.

Unidirectional and Cyclic Change in Earth’s History

• Unidirectional Changes: Irreversible transformations such as the Moon’s formation, planetary differentiation, evolution of continents, development of the atmosphere, and the emergence of life.
• Cyclic Changes: Recurring processes including the supercontinent cycle, sea-level rise and fall, the rock cycle, and biogeochemical cycles (carbon, hydrologic).

The Carbon Cycle and Greenhouse Effect

• Carbon and Hydrologic Cycles: The movement of carbon and water through Earth’s reservoirs drives climate, weathering, and biological activity.
• Greenhouse Gases: CO₂ and CH₄ trap heat, regulating the planet’s temperature through the greenhouse effect. Human activities are increasing these gases, shifting the climate balance.

Evidence from the Past: Paleoclimate and Climate Cycles

• Paleoclimate Records: Sediment and ice cores, isotope ratios, and tree rings reveal climate changes over millions of years.
• Long-term Trends: Cretaceous “greenhouse” intervals and Pleistocene ice ages alternate as part of Earth's natural rhythm.
• Short-term Climate Shifts: Milankovitch cycles (eccentricity, tilt, precession), volcanic eruptions, and solar output cause rapid changes like the Younger Dryas and Medieval Warm Period.

Modern Climate Change and Human Impact

• Recent Warming: Instrumental records and scientific evidence show sharp increases in atmospheric CO₂, global temperature, sea-level rise, shrinking glaciers, and permafrost thaw.
• Human Drivers: Fossil fuel combustion, deforestation, agriculture, and industrial emissions have pushed Earth into a new epoch—the Anthropocene.
• Impacts: Melting ice, stronger storms, ocean acidification, loss of biodiversity, shifting climate zones, and coastal flooding.
• Other Human Effects: Pollution (air, water, ozone depletion), land use changes, and resource overexploitation contribute to ecosystem change and mass extinction risk.

Future Scenarios for Earth

• Possible futures include further warming, sea-level rise, stronger storms, and long-term geologic changes like new supercontinents or even the distant expansion of the Sun.
• Strategies for a sustainable future require understanding biogeochemical cycles, reducing emissions, protecting ecosystems, and adapting to ongoing change.

Conclusion: Facing Global Change

The Earth System is dynamic, shaped by both slow geologic cycles and rapid anthropogenic shifts. Grasping these changes—past, present, and future—is essential for making informed choices in the Anthropocene.

For a visual and audio summary, watch the full chapter video on YouTube. And don’t forget to subscribe to Last Minute Lecture for more textbook chapter breakdowns and up-to-date climate change resources.

Continue learning with the Earth: Portrait of a Planet complete chapter playlist.

If you found this breakdown helpful, be sure to subscribe to Last Minute Lecture for more chapter-by-chapter textbook summaries and academic study guides.