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)