6.2B Climate change Notes

1. Climate change affects ecosystems at local, regional and global scales, altering their structure, functioning and long-term stability.
2. Changes in temperature, precipitation, sea levels and extreme events disrupt species interactions, nutrient cycles, food webs and energy flows.
3. Reduced ecosystem resilience and significant environmental stress may force entire ecosystems to reorganize, move or collapse, leading to biome shifts.

Local Impacts

Coral Bleaching

1. Corals have a symbiotic relationship with zooxanthellae, which provide them with nutrients and colour.
2. Increased sea temperature causes corals to expel these algae, resulting in bleaching.
3. If stressful conditions persist, corals starve and die.
4. Bleaching events have intensified globally due to warming oceans and increased frequency of marine heatwaves.

Desertification

1. Desertification results from the spread of dry, degraded land into once-productive ecosystems.
2. It is accelerated by reduced rainfall, increased evaporation, overgrazing, deforestation, soil erosion, and climate change.
3. Loss of vegetation reduces soil stability, leading to dust storms, reduced carbon storage, and biodiversity decline.

Regional-Scale Impacts

Poleward and Altitudinal Migration

1. Warmer temperatures shift biomes northward in the Northern Hemisphere and southward in the Southern Hemisphere.
2. Species move higher in altitude, replacing cold-adapted species.
3. Tundra and boreal forests are especially vulnerable due to limited room for migration.

Changes in Ecosystem Productivity

1. Rising CO₂ can increase plant growth via the carbon fertilisation effect.
2. However, nutrient limitations (especially nitrogen), drought and heat stress reduce long-term productivity.
3. Increased pests, invasive species, and wildfires further reduce resilience.

Global Impacts

1. Sea-Level Rise

1. Sea level increases from thermal expansion and melting glaciers/ice sheets.
2. Current rates are the highest in at least 2800 years.
3. Rising seas inundate wetlands, reduce coastal biodiversity and cause saltwater intrusion into aquifers.

2. Changes in Ocean Circulation

1. The thermohaline circulation depends on temperature and salinity differences.
2. Melting ice dilutes seawater, reducing density and slowing circulation.
3. Disruption affects marine ecosystems, nutrient cycling and regional climates.

3. Ocean Acidification

1. CO₂ dissolves in oceans, forming carbonic acid and lowering pH.
2. Acidification weakens shells, corals and plankton, altering marine food webs.
3. Reef tourism and fisheries decline.

Ecosystem Resilience and Factors Affecting It

1. Biodiversity: High biodiversity increases resilience as species can substitute roles.
2. Genetic diversity: Genetic variation enables adaptation to changing conditions.
3. Large storages: Systems with large biomass or soil nutrient stores recover faster.
4. Ecosystem complexity: More trophic interactions create stability and buffer disturbances.
5. Human pressure: Logging, pollution and overfishing reduce resilience.

Biome Shifts Due to Climate Change

1. As temperatures increase, biomes shift toward the poles or to higher elevations.
2. Tundra is invaded by shrubs and boreal forests during warming periods.
3. Temperate forests may shift northward or experience major species loss.

Climate Change Impacts Human Societies and Affects Societal Resilience

1. Climate change affects societies differently depending on wealth, infrastructure, geography, and adaptive capacity.
2. Impacts occur at local, national and global scales, influencing health, water resources, economic stability, agriculture, migration and infrastructure.
3. Vulnerable populations, such as low-income communities and climate-exposed workers, bear the greatest burden.

Impacts on Water Supply

1. Rising temperatures increase evaporation rates and reduce water availability.
2. Glacial melt initially increases flow but eventually reduces long-term water supplies.
3. Drought frequency increases in many regions.
4. Water quality deteriorates during extreme weather events.

Impacts on Agriculture

1. Temperature increases and rainfall variability reduce crop yields.
2. Pests and pathogens spread into newly warm regions.
3. Crop-growing zones shift toward the poles.
4. Heat and water stress reduce labour productivity and food availability.

Impacts on Human Health

1. Warmer temperatures expand the range of vector-borne diseases such as malaria and dengue.
2. Heatwaves increase deaths due to dehydration, heat stroke and cardiovascular stress.
3. Air pollution worsens as heat accelerates chemical reactions that produce smog.

Impacts on Infrastructure

1. Roads buckle during heatwaves.
2. Flooding damages coastal housing, railways and metro systems.
3. Ports and airports near coastlines face increasing disruption.
4. Wildfires destroy power lines, pipelines and settlements.

Urban Heat Islands (UHI)

1. Cities with dense infrastructure absorb and retain heat, increasing local temperatures.
2. Low-income areas often lack vegetation, intensifying heat exposure.
3. High UHI intensity increases health risks and energy demand.

Impacts on Migration and Social Stability

1. Sea-level rise and extreme events displace coastal populations.
2. Declining agricultural productivity contributes to food insecurity.
3. Resource scarcity may escalate conflict, especially over water and arable land

Systems diagrams and models

1. Used to visualise interactions among atmosphere, hydrosphere, biosphere, cryosphere and lithosphere.
2. Show flow of energy and matter in climate systems.
3. Support identification of positive and negative feedback loops.

Positive Feedback Loops

1. Terrestrial Albedo Reduction

1. Warming reduces snow and ice cover.
2. Dark surfaces absorb more heat.
3. Increased absorption leads to further warming.
4. Further warming reduces snow. and cycle reinforces itself.

2. Methane Release from Permafrost

1. Rising temperatures thaw permafrost layers.
2. Methane is released from previously frozen organic matter.
3. Atmospheric methane increases, trapping more heat.
4. Increased heat causes further thawing.

Negative Feedback Loops

1. Increased Cloud Formation

1. Higher evaporation increases cloud cover.
2. Some clouds reflect incoming solar radiation.
3. Reflection reduces surface heating.
4. Cooling counteracts initial warming to some extent.

2. Enhanced Plant Growth (Short-Term)

1. Higher CO₂ levels increase photosynthesis rates.
2. Vegetation absorbs more CO₂.
3. Reduced atmospheric CO₂ slows warming.
4. Limited by nutrient availability (especially nitrogen), so only temporary.

Global Energy Balance

1. Controlled by the relationship between incoming solar radiation and outgoing terrestrial radiation.
2. Influenced by:
   1. Greenhouse gases
   2. Clouds and aerosols
   3. Land surface characteristics (albedo)
   4. Ocean-atmosphere heat exchange
3. Imbalances lead to temperature changes and altered climate patterns.

Evidence suggesting Earth has exceeded the planetary boundary for climate change

1. Climate boundary set at 350 ppm CO₂ and +1 W/m² radiative forcing.
2. Current levels exceed 417 ppm CO₂ and 2.91 W/m² radiative forcing.

Evidence for Exceeding the Boundary

1. Global average temperature already +1.1°C above pre-industrial levels.
2. Melting of Greenland and Antarctic ice accelerating.
3. Long-term sea level rise (20+ cm since 1880).
4. More frequent heatwaves, storms and droughts.
5. Ocean warming and acidification increasing.
6. Increased wildfire intensity globally.

Tipping Points at Risk

1. Greenland Ice Sheet collapse.
2. Atlantic thermohaline circulation slowdown.
3. Amazon rainforest dieback.
4. Thawing of northern permafrost.
5. Coral reef die-off under warming oceans.

Perspectives on climate change among individuals and societies

Factors Influencing Perspectives

1. Geography (coastal, high-latitude, drought-prone areas).
2. Income level and resource access.
3. Education and scientific literacy.
4. Cultural beliefs and traditional practices.
5. Political ideology and media exposure.
6. Personal experience of climate impacts.

Differing Perspectives

1. Highly Vulnerable Populations

1. Residents of Maldives, Tuvalu, Bangladesh view climate change as immediate threat.
2. Indigenous communities (Inuit, Saami) experience cultural disruption due to warming Arctic.

2. Political Perspectives

1. Some leaders minimise or deny impacts due to economic priorities or ideological beliefs.
2. Policy responses influenced by partisan alignment.

3. Youth Activism

1. Young individuals demand urgent action due to long-term consequences.
2. Influential advocates (e.g., Greta Thunberg) push for stronger global climate commitments.