H2 Biology Extension B - Climate Change: Greenhouse Gases, Ecosystems, and Disease Vectors

Step 1 - The enhanced greenhouse effect

The greenhouse effect is a natural process that keeps the Earth warm enough to support life.

Step 1 - The enhanced greenhouse effect

Short wave radiation from the sun passes through the atmosphere and is absorbed by the Earth's surface, which then re-emits it as long wave infrared radiation.

Step 1 - The enhanced greenhouse effect

Greenhouse gases such as carbon dioxide and methane absorb and re-emit this infrared radiation, trapping heat in the atmosphere.

Step 1 - The enhanced greenhouse effect

The problem is the enhanced greenhouse effect: human activities like burning fossil fuels and deforestation have dramatically increased atmospheric carbon dioxide and methane concentrations, causing global temperatures to rise beyond natural levels.

Step 2 - Impact on ecosystems: coral bleaching and habitat loss

Rising sea temperatures directly stress marine organisms, particularly coral reefs.

Step 2 - Impact on ecosystems: coral bleaching and habitat loss

Corals have a mutualistic relationship with zooxanthellae, photosynthetic algae that live within their tissues and provide them with glucose.

Step 2 - Impact on ecosystems: coral bleaching and habitat loss

When water temperatures rise by just one to two degrees Celsius above the summer maximum, corals expel their zooxanthellae in a process called coral bleaching.

Step 2 - Impact on ecosystems: coral bleaching and habitat loss

Without the algae, corals lose their colour, their main energy source, and eventually die if conditions do not return to normal.

Step 2 - Impact on ecosystems: coral bleaching and habitat loss

This cascading effect reduces biodiversity because coral reefs support roughly twenty five percent of all marine species.

Step 3 - Effects on food security and agriculture

Climate change threatens global food security through multiple pathways.

Step 3 - Effects on food security and agriculture

Higher temperatures can reduce crop yields because many staple crops have an optimal temperature range, and exceeding it impairs photosynthesis and increases transpiration water loss.

Step 3 - Effects on food security and agriculture

Changes in rainfall patterns create droughts in some regions and flooding in others, both of which damage harvests.

Step 3 - Effects on food security and agriculture

Rising carbon dioxide levels may initially boost photosynthesis in C three plants, but this benefit is offset by reduced nutritional quality of crops, particularly lower protein and mineral content.

Step 4 - Biodiversity loss and shifting species distributions

As habitats warm, species distributions shift towards the poles or to higher altitudes in search of suitable conditions.

Step 4 - Biodiversity loss and shifting species distributions

Species that cannot migrate fast enough or adapt quickly enough face extinction.

Step 4 - Biodiversity loss and shifting species distributions

This is especially critical for species with small populations, limited dispersal ability, or those restricted to isolated habitats like mountaintops.

Step 4 - Biodiversity loss and shifting species distributions

Phenological mismatches also occur - for example, if spring arrives earlier, plants may flower before their pollinators have emerged, disrupting reproductive success for both species.

Step 5 - Mosquito-borne diseases and the Singapore context

Rising temperatures expand the geographic range of disease vectors, particularly mosquitoes.

Step 5 - Mosquito-borne diseases and the Singapore context

Aedes aegypti, the primary vector for dengue fever, thrives in warm, humid conditions.

Step 5 - Mosquito-borne diseases and the Singapore context

Higher temperatures shorten the mosquito's development time, increase its biting rate, and accelerate viral replication within the mosquito, all of which increase disease transmission.

Step 5 - Mosquito-borne diseases and the Singapore context

In Singapore, the National Environment Agency runs Project Wolbachia, which releases male Aedes mosquitoes infected with Wolbachia bacteria.

Step 5 - Mosquito-borne diseases and the Singapore context

When these males mate with wild females, the resulting eggs do not hatch, reducing the mosquito population without using chemical pesticides.