Climate Change and Biology
Understand the enhanced greenhouse effect, examine how species respond to climate change through migration, adaptation, and extinction, and explore the causes and consequences of coral bleaching.
The Greenhouse Effect
The greenhouse effect is a natural process where certain gases in the atmosphere (CO2, CH4, N2O, water vapour) trap outgoing infrared radiation, warming the Earth's surface to a habitable temperature (~15 degrees C). The enhanced greenhouse effect results from increased concentrations of these gases due to human activities, leading to global warming.
Enhanced Greenhouse Effect
Solar Radiation
Short-wave radiation from the Sun passes through the atmosphere
Earth Absorbs & Re-radiates
Earth's surface absorbs radiation and re-emits long-wave infrared radiation
Greenhouse Gases Trap Heat
Increased CO2 and CH4 trap more infrared radiation, raising global temperatures
Key point: The natural greenhouse effect is essential for life. The enhanced greenhouse effect is the problem -- human activities (burning fossil fuels, deforestation, agriculture) have increased atmospheric CO2 from ~280 ppm (pre-industrial) to over 420 ppm, causing rapid warming.
Species Responses to Climate Change
As temperatures and weather patterns change, species must adapt, migrate, or face extinction. The rate of current climate change is faster than most species can evolve through natural selection, making migration and behavioural plasticity critical survival strategies.
Three Possible Responses
Migration
Species shift ranges poleward or to higher altitudes to track suitable conditions (e.g., butterflies moving north)
Adaptation
Changes in phenology (timing of breeding, migration, flowering) or genetic adaptation over generations
Extinction
Species unable to adapt or migrate face population decline and extinction (e.g., specialist species with narrow tolerances)
Australian Examples
Great Barrier Reef: Rising sea temperatures cause mass coral bleaching events, threatening the world's largest coral reef ecosystem.
Mountain pygmy possum: This alpine species faces habitat loss as snow cover decreases and temperatures rise in the Australian Alps.
Phenology shifts: Many Australian bird species are breeding earlier in the season in response to warmer spring temperatures.
Coral Bleaching
Coral bleaching occurs when environmental stress causes corals to expel their symbiotic algae (zooxanthellae), turning them white. These algae provide up to 90% of the coral's energy through photosynthesis. Without them, corals starve and may die if conditions do not return to normal quickly.
Coral Bleaching Process
Healthy Coral
Zooxanthellae live in coral tissue, providing colour and energy via photosynthesis
Temperature Stress (+1-2 degrees C)
Sea surface temperature rises above normal summer maximum for sustained period
Bleached Coral
Coral expels zooxanthellae, turns white, loses primary energy source
Ecosystem Consequences
- 1. Biodiversity loss: Coral reefs support 25% of all marine species. Reef degradation threatens entire food webs.
- 2. Ocean acidification: Increased CO2 absorbed by oceans lowers pH, reducing corals' ability to build calcium carbonate skeletons.
- 3. Economic impacts: Loss of fisheries, tourism revenue, and coastal protection provided by healthy reefs.
- 4. Positive feedback: Dead reefs absorb more heat; reduced marine photosynthesis means less CO2 removal from the atmosphere.
Key Vocabulary
Enhanced Greenhouse Effect
The increase in the natural greenhouse effect caused by higher concentrations of greenhouse gases from human activities, leading to global warming.
Coral Bleaching
The expulsion of symbiotic zooxanthellae algae from coral tissue due to stress (primarily elevated temperature), causing corals to turn white and potentially die.
Phenology
The study of periodic life cycle events (migration, flowering, breeding) and how they are influenced by seasonal and climate variations.
Ocean Acidification
The decrease in ocean pH caused by absorption of excess atmospheric CO2, which reacts with water to form carbonic acid, affecting marine organisms that build calcium carbonate structures.
Worked Examples
Explain the biological mechanism of coral bleaching and why it threatens reef ecosystems.
Step 1: Corals have a mutualistic symbiosis with zooxanthellae (dinoflagellate algae). The algae photosynthesise and provide the coral with up to 90% of its energy, while the coral provides shelter and CO2.
Step 2: When sea temperatures rise 1-2 degrees C above the normal summer maximum for several weeks, the algae produce damaging reactive oxygen species. The coral expels the algae in a stress response, turning white (bleaching).
Answer: Without zooxanthellae, the coral loses its main energy source and may die if the stress persists for more than a few weeks. Since reefs are foundation ecosystems supporting ~25% of marine species, widespread bleaching causes cascading biodiversity loss throughout the food web.
Describe how a species might respond to warming temperatures by shifting its geographic range.
Step 1: Each species has a thermal tolerance range. As average temperatures rise, conditions at the warm edge of the range become unsuitable.
Step 2: The species' range shifts poleward (towards higher latitudes) or to higher altitudes where temperatures are cooler.
Answer: For example, many European butterfly species have shifted their ranges northward by 35-240 km over the past few decades in response to warming. However, species that are already at mountain tops or polar regions have nowhere to migrate and face extinction.
Explain how ocean acidification affects marine organisms with calcium carbonate shells or skeletons.
Step 1: Excess atmospheric CO2 dissolves in seawater: CO2 + H2O → H2CO3 (carbonic acid), which dissociates and lowers ocean pH.
Step 2: Lower pH reduces the concentration of carbonate ions (CO32-) needed by organisms to build CaCO3 shells and skeletons.
Answer: Organisms like corals, molluscs, and foraminifera struggle to calcify in acidified waters. Existing CaCO3 structures may even dissolve. This weakens shells and coral skeletons, reducing growth rates and structural integrity, threatening entire marine food webs.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
The enhanced greenhouse effect is caused by:
Question 2
During coral bleaching, corals turn white because:
Question 3
A species most at risk of extinction from climate change would be one that:
Question 4
Ocean acidification reduces the ability of marine organisms to:
Question 5
An example of a phenological response to climate change is:
Key Concepts Summary
- ●The enhanced greenhouse effect from human-produced CO2 and CH4 is causing global temperatures to rise faster than natural cycles.
- ●Species respond to climate change by migrating (range shifts), adapting (phenological or genetic changes), or facing extinction.
- ●Coral bleaching occurs when elevated temperatures cause corals to expel their symbiotic zooxanthellae, threatening reef biodiversity and ecosystem services.
- ●Ocean acidification (from dissolved CO2) reduces carbonate availability, impairing shell and skeleton formation in marine organisms.
- ●Specialist species with narrow tolerances and limited mobility are most vulnerable to rapid climate change.