Climate Change (Leaving Cert Geography): Revision Notes
Climate change
Climate change refers to long-term shifts in global temperatures and weather patterns. While climate variations occur naturally, human activities since the Industrial Revolution have become the primary driver of climate change through increased greenhouse gas emissions.
Natural cycles of climate change
Earth's climate has shifted throughout history due to natural processes operating over different timescales, from decades to millions of years. These natural variations provide important context for understanding current climate change.
Understanding natural climate cycles helps scientists distinguish between natural variations and human-caused changes in our current climate system.
Milankovitch cycles
These astronomical cycles drive long-term climate variations by altering how much solar energy Earth receives and where it's distributed. The three main components work together over thousands of years:
- Eccentricity: Earth's orbital shape changes from circular to elliptical over approximately 100,000 years
- Axial tilt: The angle of Earth's axis shifts over a 41,000-year cycle, affecting seasonal contrasts
- Precession: Earth's rotational wobble occurs over roughly 26,000 years
These cycles influence the timing and intensity of ice ages and warmer interglacial periods, such as the Pleistocene ice ages.
Milankovitch cycles operate on much longer timescales than current climate change, which is happening over decades rather than millennia.
Solar activity variations
The sun's energy output fluctuates through cycles of higher and lower activity, typically over an 11-year period. Sunspot activity and solar radiation levels can influence global temperatures, though their impact is generally smaller than other climate drivers.
Volcanic eruptions
Major volcanic eruptions create short-term climate cooling by releasing vast quantities of ash and sulphur dioxide into the atmosphere. These particles form an aerosol layer that reflects sunlight away from Earth's surface. The 1815 Mount Tambora eruption famously caused the "Year Without a Summer" in 1816.
Volcanic cooling effects are temporary, typically lasting 1-3 years, while greenhouse gas warming has long-lasting effects spanning decades to centuries.
The greenhouse effect
Natural greenhouse effect
The greenhouse effect is a vital natural process that maintains Earth's temperature within a range suitable for life. Here's how it works:
- Solar radiation reaches Earth's atmosphere
- Some energy reflects back to space, while the rest is absorbed by the surface
- Earth's surface re-radiates this energy as infrared heat
- Greenhouse gases in the atmosphere trap some of this heat, preventing it from escaping to space
- This trapped heat warms Earth's surface and lower atmosphere
Key greenhouse gases include water vapour, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).
Without this natural process, Earth's average temperature would be approximately -18°C instead of the current 15°C, making the planet uninhabitable for most life forms.
Human-enhanced greenhouse effect
Human activities have intensified the natural greenhouse effect, often called anthropogenic global warming. This enhancement occurs through increased emissions of greenhouse gases, which trap more heat in the atmosphere than the natural balance requires.
Causes of the enhanced greenhouse effect
Fossil fuel combustion
Burning coal, oil, and natural gas for energy and transport represents the largest source of greenhouse gas emissions. These activities release carbon dioxide that was previously stored in Earth's crust for millions of years, rapidly increasing atmospheric CO₂ concentrations.
Real-world Impact: Coal Power Plant
A typical coal-fired power plant burns approximately 1.4 million tonnes of coal per year, releasing about 3.7 million tonnes of CO₂ into the atmosphere - equivalent to the emissions from about 800,000 cars.
Deforestation
Clearing forests for agriculture, urban development, or logging reduces the number of trees available to absorb CO₂ from the atmosphere. This process also releases stored carbon when trees are cut down and decay or burn.
Industrial processes
Manufacturing industries like cement production, steelmaking, and chemical production emit significant quantities of CO₂ and other greenhouse gases including methane (CH₄) and nitrous oxide (N₂O).
The result is a gradual but accelerating increase in Earth's average surface temperature. Unlike the natural greenhouse effect, which maintains stable temperatures, the enhanced effect causes unnatural and rapid global temperature rises.
The current rate of CO₂ increase is approximately 100 times faster than natural variations, demonstrating the unprecedented nature of human impact on climate.
Consequences of the enhanced greenhouse effect
Global warming
Rising average global temperatures drive broader climate changes, altering weather patterns, precipitation, and seasonal cycles worldwide.
Extreme weather events
Climate change increases both the frequency and severity of extreme weather, including more intense hurricanes, prolonged droughts, severe flooding, and unprecedented heatwaves.
Melting ice caps and glaciers
Higher temperatures cause widespread melting of polar ice sheets, mountain glaciers, and sea ice. This contributes to rising sea levels and threatens coastal communities while destroying critical habitats for polar species.
Ocean acidification
Oceans absorb excess CO₂ from the atmosphere, which increases their acidity. This chemical change harms marine ecosystems, particularly affecting coral reefs and shellfish that struggle to build and maintain their calcium carbonate structures in more acidic water.
Ocean acidification is often called "the other CO₂ problem" because it occurs alongside global warming but affects marine life through different chemical processes.
Key Points to Remember:
- Natural climate change occurs through Milankovitch cycles, solar variations, and volcanic eruptions over long timescales
- The natural greenhouse effect is essential for life, keeping Earth warm enough to be habitable
- Human activities have enhanced the greenhouse effect through fossil fuel burning, deforestation, and industrial processes
- The enhanced greenhouse effect causes global warming and leads to extreme weather, ice melting, and ocean acidification
- Without greenhouse gases, Earth would be about 33°C colder than it currently is