Climate Change Impacts on Natural and Human Systems

Topic 2.3: Impact of Climate Change on NATURAL SYSTEMS

• Natural systems consist of natural processes on Earth and all living and non-living things.
• These are interconnected, like an ecosystem with predator-prey relationships.
• Climate change, with warming trends, extreme weather, and rising sea levels, impacts both nature/wildlife (physical systems) and human societies (human systems).
  • Topic 2.3 focuses on natural systems.

1) Natural Systems

a) Increase in atmospheric & ocean temperatures

• Since the industrial revolution in the early 1900s, Earth’s atmospheric temperature has been increasing due to emissions of greenhouse gases (GHG).
• Most excess heat trapped by GHGs is absorbed by oceans; sea surface warmed by about $1°C$ from 1880 to 2020.
• This increase isn't uniform globally.

b) Changes to ocean circulation

• Oceans redistribute heat globally.
• Ocean currents move warm water from the equator to the poles.
• Water cools at the poles, becomes denser, and sinks, forming cool subsurface flows.
• Warmer, less dense water replaces the sinking water, rising to the surface in a cycle, a 'conveyor belt' system.
• Due to increased ocean temperatures from climate change, surface water gains more heat and becomes less dense. This makes it harder for water to sink, reducing the amount of water near the poles.
  • Studies show ocean currents in the Atlantic Ocean slowed down by 15%.
• The global circulation of water will slow down and affect the circulation of heat around the world.

c) Changes to precipitation on land

Increase in precipitation

• As temperature increases, warmer air holds more water vapor, especially near water bodies.
• More moisture in the air leads to more intense precipitation and heavy rain.
  • When the Earth warms by $3°C$, some areas, especially at the North and South Poles, parts of Southeast Asia, and central Africa, will see a rise in heavy rain.
  • This may lead to increased floods.

Decrease in precipitation

• Increased temperature leads to a higher rate of evaporation, reducing surface moisture and drying out soil and vegetation.
• Lack of surface moisture further reduces rain occurrence.
• Increased drought risks in drier subtropical areas (deserts) and mid-latitudes (e.g., Southwest USA, Sahel region in Africa).
• Dry areas become drier, increasing droughts.

2) Aquatic (marine) ecosystems

a) Disruption of marine food webs

• Changes in ocean circulation disrupt marine food webs.
• Ocean currents transport heat and allow the exchange of nutrients/oxygen between surface and deep waters.
• Slowing ocean circulation reduces the mixing of warm surface waters with cooler, deeper water.
• Aquatic organisms near surface waters, especially phytoplankton (marine algae/bacteria), won't get nutrients from the deep ocean.
  • Slowing of the Atlantic Ocean current has led to a 10% drop in phytoplankton since the 1800s.
• Species higher in the food chain will decrease due to lack of food, affecting the ecosystem.
• Some marine creatures are unable to adapt, risking extinction and causing the entire food web to collapse.
• Small fish, shrimp, snails, and jellyfish feed on phytoplankton. These creatures are then eaten by larger animals, such as fish, sharks, corals, and whales.

b) Ocean acidification & coral bleaching

• Ocean acidification: oceans absorb carbon dioxide from the atmosphere, forming carbonic acids, making the oceans acidic.
• Phytoplankton absorb carbon dioxide through photosynthesis. Less phytoplankton means increased carbon dioxide and more carbonic acids.
• Carbonic acids dissolve calcium carbonate, needed by marine organisms like corals, mussels, and oysters to form skeletons and shells.
• Coral bleaching: corals expel algae living within their tissues, losing vibrant colors and turning white.
• Algae help make food for corals through photosynthesis. Expulsion happens when water is too warm, preventing photosynthesis.
  • The Great Barrier Reef in Australia was severely affected in 2016 and 2017 due to rising sea temperatures.
  • Up to two-thirds of corals died in the northern section, causing a drastic decrease in species diversity.
• Ocean acidification means marine organisms can't form shells/skeletons, making them vulnerable to predators and leading to an unstable food web.
• Coral bleaching means organisms lose their food source and habitat.

3) Terrestrial (land) ecosystems

a) Threats to flora and fauna due to increased atmosphere temperatures

• Changes in geographic distribution of terrestrial species: species adapt or migrate to find new habitats in higher latitudes/altitudes with cooler temperatures.
  • Australia’s mountain pygmy possums are at high extinction risk due to fewer cold environments.
  • Australia’s wallabies migrating to higher lands may compete for food with existing species.
• Animals migrate to escape higher temperatures, but those unable to survive in new environments risk extinction.
• Drying up of wetlands and forests has killed thousands of plant and animal species.
• Droughts can result in the spread of diseases and have caused thousands of animal deaths.
• Plants can also be uprooted by flood waters and terrestrial species may drown.

b) Threats to flora and fauna due to extreme weather

Impact of Droughts:

• Plants are vulnerable to water scarcity and cannot obtain alternative water sources, resulting in them eventually withering and dying
  • Drought in California, USA between 2012 to 2016 led to the death of 102 million forest trees due to the lack of water and the spread of diseases.
  • Desert bighorn sheep in California became extinct due to reduced food sources in forests
• While droughts may force animals to move to new locations in search of water, food and habitat, some species may not be able to adapt as quickly.

Impact of Intense Rainfall:

• Intense rainfall can lead to soil erosion, removing nutrients important for plant growth and making it more difficult for plants to survive.
• Huge amounts of water entering rivers can cause rivers to overflow their banks, resulting in floods. Plants can also be uprooted by flood waters and terrestrial species may drown.

Topic 2.4 - How does climate change impact HUMAN SYSTEMS?

1) Direct Impacts on Humans

a) Injuries, loss of human lives

• Heat waves: periods of excessively hot weather abnormal for a location, lasting a few days or longer. Temperatures can be more than $40°C$.
  • Europe's heat waves in 2003 and 2019 led to ~70,000 deaths.
  • Temperatures of $45°C$ were recorded in France and Italy.
• Wildfires: uncontrolled fires in natural areas.
  • Southern California wildfires in January 2025 killed at least 29 people, forced >200,000 to evacuate, and destroyed >18,000 homes/structures.
• Tropical cyclones: intense storms over warm tropical oceans, also known as typhoons/hurricanes.
  • In 2020, the Philippines was hit by six tropical cyclones with Typhoon Goni causing massive destruction.
    Heat waves can cause heat stroke, difficulty breathing, and death.
    Wildfires can cause suffocation, burns, heat-related injuries, and respiratory illnesses.

b) Destruction of property & increased poverty

• Destruction of buildings and properties can result in homelessness and economic losses after wildfires and tropical cyclones.
  • Almost 1 million people had to be evacuated, and crop damage amounted to $36 million in the Philippines in 2020.

2) Indirect Impacts on Humans

a) Affects provisioning ecosystem services

• Rising sea levels can cause saltwater to enter rivers, threatening freshwater fisheries.
• Aquatic species may die with sudden water quality changes.
• Heat waves, droughts, floods, cyclones, and wildfires can destroy crops, affecting food production.
  • In Cambodia, declining water levels in Tonle Sap lake has reduced fish habitats.
  • Thailand experienced its worst drought in 2020 with a lack of rain, leading to reduced crops.
• This threatens economic livelihoods and food security and increases food prices, affecting the poor most.

b) Affects regulating ecosystem services

• Higher global temperatures create conducive environments for vectors like mosquitoes and ticks to breed, increasing the risk of vector-borne diseases.
  • Malaria, dengue fever, and Zika are responsible for >700,000 deaths annually.
  • Bhutan suffered their first national dengue virus outbreak in 2019.
• More sick people reduces the country's productivity level, increasing the healthcare burden, and reducing economic growth.

c) Affects cultural ecosystem services

• Climate change may destroy natural landscapes, reducing tourism.
  • Melting Arctic ice has increased tourism opportunities but also threatens low-lying islands like the Maldives, which rely on tourism for economic growth.
• This reduces tourism revenue, causing individuals in related industries to lose their livelihoods.