10.4 Ecosystem services and biodiversity

Climate change is reshaping ecosystems worldwide, altering how they function and the services they provide. From shifts in species distribution to disruptions in water regulation and pollination, these changes have far-reaching consequences for both nature and human societies.

Biodiversity loss compounds the problem. As vulnerable ecosystems like coral reefs degrade, the effects cascade through food webs, disrupting pest control, nutrient cycling, and more. Understanding these impacts is the foundation for developing effective adaptation strategies.

Climate Change's Impact on Ecosystems

Ecosystem Functioning and Services

Climate change alters ecosystem functioning through three main drivers: shifting temperatures, changing precipitation patterns, and more frequent extreme weather events. Each of these disrupts the biological processes that ecosystems depend on.

• Temperature changes affect where species can survive and when seasonal events occur (phenology). Many species are shifting their ranges poleward or to higher elevations as their historical habitats warm.
• Altered precipitation patterns change water availability and overall ecosystem productivity. Some regions face prolonged drought while others experience heavier, less predictable rainfall.
• Extreme weather events like hurricanes and droughts destabilize ecosystems that took decades or centuries to develop.

These disruptions ripple through the ecosystem services humans rely on:

• Water regulation shifts as hydrological cycles change, altering groundwater recharge and river flows
• Pollination suffers when plants flower at different times than their pollinators are active, creating phenological mismatches
• Pest control weakens as predator-prey relationships shift geographically or temporally
• Nutrient cycling changes as warming alters decomposition rates and soil microbial communities

A critical concept here is tipping points: thresholds beyond which ecosystems undergo rapid, often irreversible change. The Amazon rainforest, for instance, could transition to savanna if combined deforestation and drought push it past its tipping point. Similarly, Arctic permafrost thawing releases stored carbon and methane, accelerating warming in a self-reinforcing loop.

Biodiversity Loss and Vulnerable Ecosystems

Climate change drives biodiversity loss through several interconnected pathways:

• Habitat degradation removes the physical environment species need. Melting sea ice, for example, eliminates hunting platforms for polar bears.
• Species range shifts occur as organisms track suitable climates, generally moving poleward or upslope. Species that can't move fast enough face local extinction.
• Phenological mismatches arise when interdependent species fall out of sync. If migratory birds arrive after the peak of insect emergence they depend on for food, breeding success drops.

Coral reefs are among the most climate-vulnerable ecosystems on Earth. Ocean acidification (caused by seawater absorbing excess $CO_2$) reduces the rate at which corals can build their calcium carbonate skeletons. Rising water temperatures trigger coral bleaching, where corals expel the symbiotic algae (zooxanthellae) that provide them with energy and color. Without these algae, corals starve. As reef structure degrades, the thousands of fish, crustacean, and invertebrate species that depend on reefs lose their habitat.

These ecological losses cascade into human societies through:

• Food security: reduced crop yields and shifting fish stocks
• Water availability: altered rainfall and accelerated glacier melt
• Economic stability: disrupted agriculture, fisheries, and tourism industries

Ecosystems' Role in Climate Regulation

Carbon Sequestration in Terrestrial Ecosystems

Ecosystems are active players in the global carbon cycle, functioning as both sources and sinks of greenhouse gases. How well they sequester carbon directly affects the pace of climate change.

Forests, especially tropical rainforests, are major carbon sinks. They lock up carbon in biomass (trunks, branches, leaves) and in soils through root systems and decomposing leaf litter. The Amazon rainforest alone stores an estimated 150–200 billion tons of carbon.

Wetlands and peatlands punch well above their weight. Peatlands cover only about 3% of Earth's land surface yet store roughly 30% of all soil carbon. However, when peatlands are drained or warmed, they can flip from carbon sinks to carbon sources, releasing methane (a greenhouse gas roughly 80 times more potent than $CO_2$ over a 20-year period).

Oceanic Carbon Sequestration and Climate Regulation

The ocean is the planet's largest carbon sink, and marine ecosystems drive much of that sequestration:

• Phytoplankton absorb $CO_2$ through photosynthesis, forming the base of the marine food web
• Marine vegetation such as seagrasses and mangroves store what's called blue carbon in their biomass and sediments
• The biological pump transfers organic matter produced near the surface to the deep ocean, locking carbon away for centuries or longer

Beyond carbon, ecosystems influence climate through the albedo effect. Snow-covered tundra reflects a high proportion of incoming sunlight, while darker forests absorb more. When vegetation cover changes (for example, shrubs expanding into tundra as it warms), regional temperature and precipitation patterns shift as well.

Ecosystem Degradation and Climate Feedbacks

When ecosystems degrade, they can trigger positive feedback loops that accelerate climate change:

1. Deforestation releases the carbon stored in trees and soil, while simultaneously removing future sequestration capacity.
2. Thawing permafrost releases methane and $CO_2$ that had been locked in frozen organic matter for thousands of years.
3. The additional greenhouse gases cause further warming, which drives more ecosystem degradation.

The good news is that this process can work in reverse. Ecosystem restoration enhances carbon sequestration. Reforestation, afforestation (planting trees where none existed recently), and wetland/peatland restoration all rebuild natural carbon sinks.

Biodiversity Loss and Ecosystem Resilience

Ecosystem Stability and Functioning

Biodiversity isn't just a nice thing to have; it's what makes ecosystems resilient. When an ecosystem has many species, it has functional redundancy, meaning multiple species perform similar ecological roles. If one species declines, others can compensate, keeping the system stable.

Keystone species have outsized influence on ecosystem structure. Their loss can trigger trophic cascades, where effects ripple across multiple levels of the food web. A well-studied example: when sea otter populations declined in the Pacific Northwest, sea urchin populations exploded unchecked. The urchins overgrazed kelp, and entire kelp forest ecosystems collapsed.

At an even finer scale, genetic diversity within species determines how well populations can adapt to new conditions. Cheetahs, for instance, have extremely low genetic diversity due to a historical population bottleneck. This makes them more susceptible to disease and less able to adapt to environmental change.

Impacts on Ecosystem Services and Human Well-being

Biodiversity loss directly undermines the ecosystem services that human societies depend on:

• Food provision suffers when crop and livestock diversity narrows, leaving food systems more exposed to shocks
• Water purification declines when filtering organisms in rivers, wetlands, and coastal waters disappear
• Disease regulation shifts as changes in host-pathogen dynamics can increase disease transmission to humans

Agricultural systems illustrate this vulnerability clearly. Monocultures are more susceptible to pests and diseases and less resilient to climate variability. The Irish Potato Famine (1845–1852) is a stark historical example: near-total reliance on a single potato variety meant that when blight struck, there was no genetic backup, and over a million people died.

Biodiversity also holds cultural and aesthetic value that contributes to human well-being. Eco-tourism generates revenue for communities. Traditional ecological knowledge, built over generations, often depends on the continued presence of specific species. Many ecosystems and species carry deep spiritual or cultural significance for Indigenous and local communities.

Conservation Strategies for a Changing Climate

Adaptive Management and Protected Areas

Traditional protected areas were designed for a static climate. Climate-smart conservation requires rethinking that approach.

• Protected area networks now need to account for projected species range shifts and habitat changes, not just current distributions.
• Connectivity conservation focuses on maintaining or restoring ecological corridors between protected areas so species can move as conditions change. The Yellowstone to Yukon Conservation Initiative is a large-scale example, linking habitats across over 3,200 km of the Rocky Mountains.
• Ecosystem-based adaptation integrates biodiversity conservation with climate goals. Mangrove restoration, for instance, simultaneously protects coastlines from storm surges and sequesters carbon.

Innovative Conservation Techniques

When in-place protection isn't enough, conservationists turn to more interventionist strategies:

• Ex situ conservation acts as an insurance policy. Seed banks like the Svalbard Global Seed Vault preserve plant genetic diversity, while captive breeding programs maintain populations of critically endangered species.
• Assisted migration involves deliberately relocating species to areas projected to be more suitable under future climate conditions. The Florida torreya tree, a critically endangered conifer, has been translocated to cooler northern habitats where it may have a better chance of survival. This approach is controversial because introduced species can sometimes disrupt their new ecosystems.
• Community-based conservation engages local stakeholders in managing resources. Community-managed marine protected areas in the Pacific Islands have shown strong results because local people have direct knowledge of and investment in their ecosystems.

Conservation Financing and Policy

Effective conservation requires funding mechanisms and policy frameworks that align climate and biodiversity goals:

• Payments for ecosystem services (PES) compensate landowners for maintaining forests, wetlands, or other ecosystems that provide public benefits like carbon storage or water filtration.
• REDD+ programs (Reducing Emissions from Deforestation and Forest Degradation) create financial incentives for developing countries to keep forests standing rather than clearing them.
• Policy integration means embedding biodiversity objectives into climate plans and vice versa. The European Union's Biodiversity Strategy for 2030, for example, is explicitly linked to its climate targets.
• International agreements provide the framework for coordinated action. The Convention on Biological Diversity (CBD) sets global biodiversity targets, while the Paris Agreement recognizes ecosystem-based approaches as part of the climate solution.