IB Environmental systems and societies 6.2B Climate Change Notes

Climate Impacts: Warming Reshapes Ecosystems, Oceans and Societies

1. Climate change alters ecosystem structure, functioning and long-term stability at local, regional and global scales.
2. Shifts in temperature, precipitation, sea level and extreme events disrupt species interactions, nutrient cycles, food webs and energy flows.
3. Reduced resilience can force ecosystems to reorganise, move or collapse, producing biome shifts.

Local Impacts: Warming Reshapes Ecosystems From Reefs to Drylands

Coral Bleaching

1. Corals live in symbiosis with zooxanthellae, the algae that give them nutrients and colour.
2. Higher sea temperature makes corals expel these algae, causing bleaching.
3. If stress persists, corals starve and die.
4. Bleaching has intensified globally as oceans warm and marine heatwaves grow more frequent.

Desertification

1. Desertification is the spread of dry, degraded land into once-productive ecosystems.
2. It is accelerated by reduced rainfall, higher evaporation, overgrazing, deforestation, soil erosion and climate change.
3. Vegetation loss reduces soil stability, driving dust storms, lower carbon storage and biodiversity decline.

Regional Impacts: Biomes Migrate and Productivity Swings

Poleward and Altitudinal Migration

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

Changes in Ecosystem Productivity

1. Rising CO₂ can boost plant growth through the carbon fertilisation effect.
2. Nutrient limits (especially nitrogen), drought and heat stress cut long-term productivity.
3. More pests, invasive species and wildfires further reduce resilience.

Biome Shifts Due to Climate Change

1. As temperatures rise, biomes shift toward the poles or to higher elevations.
2. Tundra is invaded by shrubs and boreal forest during warming periods.
3. Temperate forests may shift northward or lose many species.

Global Physical Impacts: Rising Seas and Acidifying Oceans

Sea-Level Rise

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

Changes in Ocean Circulation

1. Melting ice freshens the North Atlantic, lowering water density and weakening circulation.
2. A weaker Gulf Stream could cool northwestern Europe even as the planet warms.

The full AMOC and thermohaline slowdown mechanism is covered in 6.2D.

Ocean Acidification

1. CO₂ dissolves in seawater to form carbonic acid, lowering pH.
2. Acidification weakens shells, corals and plankton, altering marine food webs.
3. Reef tourism and fisheries decline as a result.

Ecosystem Resilience and the Factors That Affect It

1. Biodiversity: high biodiversity raises resilience because 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.