Hello IB Biologists! Welcome to Climate Change

Welcome to the final topic in our "Continuity and Change" section! This chapter brings together everything we have learned about ecosystems, populations, and evolution, showing how human activities are driving large-scale biological changes worldwide.

Don't worry if this topic feels overwhelming; we will break down the scientific mechanisms into clear, digestible steps. The key focus here is understanding how changes in the physical environment (climate) force biological systems (species, populations, and ecosystems) to adapt or perish—this is "change" in action.

What you will learn: The mechanism of the greenhouse effect, the biological consequences of rising temperatures and ocean acidification, and the role of living organisms in mitigating (or exacerbating) these changes.

1. Understanding the Climate System and the Greenhouse Effect

1.1 Climate vs. Weather (A Quick Clarification)

Before we dive in, let’s make sure we are using the right terms:

  • Weather: What is happening right now or over a short period (e.g., it is raining today).
  • Climate: The long-term average weather patterns in a region (e.g., this desert region is typically hot and dry year-round).

Climate Change refers to significant, long-term changes in these average patterns, primarily driven by rising global average temperatures.

1.2 The Natural Greenhouse Effect (The Essential Blanket)

The Earth’s temperature is regulated by the atmosphere in a process called the Greenhouse Effect. This effect is totally natural and essential for life!

Step-by-step Mechanism:

  1. Solar Radiation In: Short-wave radiation (light) from the Sun passes easily through the atmosphere and hits the Earth’s surface.
  2. Surface Heats Up: The Earth absorbs this energy and warms up.
  3. Heat Radiation Out: The warm Earth radiates energy back towards space, but this energy is now long-wave infrared radiation (heat).
  4. Trapping the Heat: Certain gases in the atmosphere, called Greenhouse Gases (GHGs), absorb this long-wave radiation and radiate much of it back towards Earth, trapping the heat.

Analogy: Think of GHGs like a blanket around the Earth. A natural blanket keeps us comfortable.

1.3 The Enhanced Greenhouse Effect

Human activities have greatly increased the concentration of GHGs in the atmosphere, leading to more heat being trapped. This is known as the Enhanced Greenhouse Effect, causing global warming.

Major Greenhouse Gases (GHGs)

The impact of a GHG depends on its concentration and its ability to absorb long-wave radiation.

  • Carbon Dioxide (\(CO_2\)): The most significant contributor due to its high volume, primarily from burning fossil fuels (coal, oil, gas) and deforestation.
  • Methane (\(CH_4\)): Much more potent per molecule than \(CO_2\), but less abundant. Released from melting permafrost, livestock farming (digestion), and landfill decomposition.
  • Water Vapor (\(H_2O\)): While the most abundant GHG, human activity doesn't directly control its concentration; rather, warmer temperatures increase evaporation, leading to a reinforcing cycle (a positive feedback loop).

Quick Review Box:

Mnemonic for GHGs: The major ones start with C, M, W (Cold Milk Warmth)

  • C: \(CO_2\) (Carbon Dioxide)
  • M: \(CH_4\) (Methane)
  • W: \(H_2O\) (Water Vapor)

2. Biological Consequences of Rising Temperatures

As the climate changes, biological systems face new selective pressures, leading to shifts in evolution, distribution, and survival rates. This section highlights the key impacts related to "continuity and change."

2.1 Changes in Species Distribution and Migration

When the environment becomes too hot or dry, species must either adapt, move, or die. Many are choosing to move.

  • Latitudinal Shifts: Species are migrating toward the cooler poles (North and South) to stay within their preferred temperature range (their optimum niche).
  • Altitudinal Shifts: Species living on mountains are moving higher up. For example, trees are growing closer to mountain peaks than they did decades ago.
  • The Problem of Habitat Loss: Species at the poles (like polar bears) or the highest mountain peaks have nowhere left to go. These species are highly vulnerable to extinction.

Did you know? Marine species, which rely on specific ocean temperatures, are also moving poleward much faster than land species.

2.2 Changes in Phenology (Life Cycle Timing)

Phenology is the study of the timing of recurring biological phenomena, such as flowering, migration, and breeding. Temperature is a key cue for these events.

As spring arrives earlier due to warmer temperatures, many species are experiencing "temporal mismatch."

  • Earlier Flowering: Plants may bloom weeks earlier than historical averages.
  • Earlier Migration/Breeding: Birds might begin nesting before their traditional schedule.
  • The Danger of Mismatch: If a primary consumer (e.g., an insect) relies on a plant that blooms earlier, but the secondary consumer (e.g., a migratory bird) arrives later, the bird misses its peak food source. This disrupts food webs and reduces breeding success.

2.3 Impact on Arctic and Polar Ecosystems

These regions are warming faster than any other area on Earth. Since ice cover is a crucial habitat element, the effects are catastrophic:

  • Loss of Habitat: Melting sea ice reduces the hunting grounds for polar bears and the breeding sites for seals.
  • Melting Permafrost: Thawing permafrost (permanently frozen ground) releases vast amounts of trapped organic matter, which decomposes, releasing more \(CO_2\) and \(CH_4\), creating a powerful positive feedback loop that speeds up warming further.

Common Mistake to Avoid: Climate change affects more than just average temperature. It also increases the frequency of extreme events like floods, droughts, heatwaves, and severe storms, which drastically impact population survival.

3. Ocean Acidification: The "Other" \(CO_2\) Problem

It's vital to remember that not all excess \(CO_2\) stays in the atmosphere; much of it is absorbed by the world's oceans. While the oceans act as a major carbon sink (absorbing about 25% of human emissions), this absorption comes at a steep biological cost: Ocean Acidification.

3.1 The Chemical Mechanism

When \(CO_2\) dissolves in seawater, it reacts with water (\(H_2O\)) to form carbonic acid (\(H_2CO_3\)).

\[CO_2 + H_2O \rightleftharpoons H_2CO_3\]

Carbonic acid is unstable and rapidly dissociates, releasing hydrogen ions (\(H^+\)) into the water:

\[H_2CO_3 \rightleftharpoons H^+ + HCO_3^-\ (Bicarbonate\ ion)\]

An increase in hydrogen ions (\(H^+\)) leads to a lower pH, meaning the water is becoming more acidic.

3.2 Biological Consequences of Acidification

The increasing acidity severely impacts marine life, especially organisms that build shells or skeletons made of calcium carbonate (\(CaCO_3\)).

Impact on Carbonate Availability

The excess \(H^+\) ions react with carbonate ions (\(CO_3^{2-}\)), which are essential building blocks for shells and reefs, effectively reducing the availability of carbonate ions for organisms.

\[H^+ + CO_3^{2-} \rightleftharpoons HCO_3^-\]

This process makes it harder, and eventually impossible, for organisms to build and maintain their shells and skeletons.

Vulnerable Organisms
  • Corals: Reefs are built by organisms that secrete calcium carbonate. Acidification weakens coral skeletons, leading to reef erosion and coral bleaching (loss of the symbiotic algae that provides coral with food).
  • Shellfish: Mollusks (oysters, mussels), echinoderms (sea urchins), and tiny plankton (coccolithophores, pteropods) struggle to calcify, jeopardizing their survival. Since pteropods are a major food source for juvenile salmon and cod, this threatens entire marine food chains.

Key Takeaway: Ocean acidification is a direct consequence of excess atmospheric \(CO_2\), causing fundamental changes to marine ecosystem structure, independent of warming.

4. The Role of Biology in Mitigation and Adaptation

Biological systems are not just victims of climate change; they are also crucial players in mitigating its effects and adapting to new conditions.

4.1 Enhancing Carbon Sinks

The most powerful biological way to slow climate change is to enhance natural carbon sinks—places that naturally remove \(CO_2\) from the atmosphere.

  • Forests (Terrestrial Sink): Trees remove vast amounts of \(CO_2\) through photosynthesis. Reforestation (planting trees where forests existed) and Afforestation (planting trees in new areas) are direct mitigation strategies.
  • Wetlands and Peatlands (Soil Sink): These ecosystems store massive amounts of carbon in their waterlogged soil. Protecting them prevents the carbon from being released back into the atmosphere upon drainage or drying.
  • Marine Ecosystems (Ocean Sink): Protecting marine habitats, especially mangrove forests, salt marshes, and seagrass beds (known as "blue carbon" habitats), enhances their ability to capture and store carbon in their sediments.

4.2 Managing Biodiversity for Resilience

Ecosystems with high biodiversity tend to be more resilient and better able to adapt to changing climatic conditions. Why?

  • Genetic Diversity: Within a population, a wider range of alleles means a higher chance that some individuals possess traits (e.g., heat tolerance, drought resistance) that allow them to survive new selective pressures.
  • Ecosystem Stability: Diverse ecosystems offer redundancy (many species fulfilling similar roles), meaning if one species fails, the entire ecosystem function doesn't collapse immediately.

4.3 Biological Adaptation Strategies

While humans strive for mitigation, many organisms are adapting:

  • Plasticity: Some species exhibit phenotypic plasticity—the ability to change their physical or behavioral traits in response to environmental cues (e.g., altering breeding schedules based on temperature).
  • Evolutionary Adaptation: Over multiple generations, populations might evolve through natural selection to become better suited to warmer conditions, although this process is often too slow to keep pace with the current rate of climate change.

Quick Review: Key Takeaways

  • Climate change is driven by the Enhanced Greenhouse Effect, caused primarily by human release of \(CO_2\).
  • Biological consequences include shifts in species distribution (moving poleward/upward) and disruptions in phenology (timing of life events).
  • Excess \(CO_2\) also causes ocean acidification, harming organisms that rely on calcium carbonate (corals, mollusks).
  • Biological mitigation focuses on enhancing carbon sinks (like forests and wetlands) and protecting biodiversity to increase ecosystem resilience.

You've successfully covered a challenging but essential topic! Remember, understanding the biology behind climate change is the first step toward finding effective solutions.