Climate Change 🌍

Introduction: Why climate change matters to students

Climate change is one of the biggest examples of continuity and change in biology because it shows how living things respond when the environment shifts over time. Some conditions on Earth stay stable for long periods, while others change gradually or suddenly. When the climate changes, species must adjust, move, evolve, or face decline. That makes climate change a powerful topic in IB Biology HL because it connects homeostasis, sustainability, inheritance, selection, and ecosystems.

Learning objectives

By the end of this lesson, students should be able to:

• Explain the main ideas and terminology behind climate change.
• Apply IB Biology HL reasoning to real climate data and biological examples.
• Connect climate change to continuity and change in living systems.
• Summarize how climate change fits within the broader biology course.
• Use evidence and examples to explain biological effects of climate change.

A useful hook is this: imagine a coral reef, a polar bear habitat, or a crop field that has supported people for generations. If temperature, rainfall, or sea level changes, the entire biological system can change too. 🌱🐟❄️

What climate change means in biology

Climate is the long-term pattern of weather in a region, including temperature, precipitation, humidity, wind, and seasonal trends. Climate change refers to long-term shifts in these patterns. In modern biology, the term often refers to warming caused largely by human activities, especially the increase in greenhouse gases such as $\mathrm{CO_2}$, $\mathrm{CH_4}$, and $\mathrm{N_2O}$.

The greenhouse effect is a natural process that helps Earth stay warm enough for life. Sunlight reaches Earth, and some of the energy is reflected back into space while some is absorbed by land and oceans. Earth then emits infrared radiation. Greenhouse gases absorb and re-radiate some of this heat, keeping the planet warmer. The problem arises when human activity increases greenhouse gas concentrations, strengthening this effect and changing the global energy balance.

Important terms to know include:

• Greenhouse gases: gases that absorb infrared radiation.
• Carbon footprint: the total greenhouse gas emissions associated with a person, product, or activity.
• Anthropogenic: caused by human activity.
• Mitigation: actions that reduce the causes of climate change.
• Adaptation: actions that reduce the damage caused by climate change.

A simple example is transportation. Burning fossil fuels in cars and planes releases $\mathrm{CO_2}$, adding to the atmosphere. That extra gas contributes to warming, which can alter rainfall patterns and increase extreme weather. 🚗🌫️

How climate change affects living organisms

Climate change affects biology because organisms depend on stable environmental conditions. Temperature, water availability, and season length influence enzyme activity, reproduction, distribution, and survival.

For example, many enzymes work best in a narrow temperature range. If temperature rises too high, enzyme activity can decrease because the protein’s shape changes. This can affect metabolism, growth, and reproduction. In plants, warmer conditions can increase evaporation and lead to drought stress. In animals, heat stress can make it harder to maintain homeostasis.

Climate change also shifts habitats. Species may move toward the poles, to higher altitudes, or to deeper waters where temperatures are cooler. However, not all species can move quickly enough. Plants, coral, and some amphibians may be especially vulnerable because they are less mobile or depend on very specific conditions.

A real-world example is coral bleaching. Corals live in symbiosis with algae called zooxanthellae. When sea temperatures rise, corals become stressed and may expel the algae. Without them, the coral loses color and much of its energy supply. If the stress continues, the coral can die. This affects reef biodiversity because many organisms depend on coral reefs for food and shelter. 🪸

Climate change also changes timing in nature. Migration, flowering, breeding, and insect emergence may occur earlier or later than before. If the timing of one species changes but its food source does not, the match between species can break down. This is called a phenological mismatch.

Evidence for climate change and how biologists study it

IB Biology HL expects students to use evidence. Climate change is supported by data from temperature records, ice cores, sea level measurements, glacier retreat, ocean warming, and changes in species distributions.

Scientists often compare long-term data sets. For example, ice core samples contain trapped air bubbles that reveal past atmospheric gas concentrations. These data show that current $\mathrm{CO_2}$ levels are much higher than pre-industrial levels. Satellite measurements also show shrinking ice cover and changes in vegetation patterns across many regions.

Biologists may use graphs to identify trends. A line graph of mean global temperature over time often shows an upward trend with natural variation from year to year. When interpreting data, it is important to distinguish between correlation and causation. For example, rising temperatures may correlate with earlier spring flowering, but the biological mechanism is that warmth affects developmental timing.

A useful IB-style reasoning step is to ask:

1. What is the independent variable? For climate studies, this could be temperature, $\mathrm{CO_2}$ concentration, rainfall, or time.
2. What is the dependent variable? This could be species abundance, growth rate, fertility, or distribution.
3. What are the controls? These are conditions kept constant, such as light intensity, soil type, or initial population size.

Example: A school investigation might compare plant growth under two temperature conditions while keeping light, water, and soil the same. If the warmer group grows less well, this may suggest that the species is sensitive to heat stress. That kind of reasoning mirrors experimental thinking in IB Biology HL. 📊

Climate change, natural selection, and evolution

Climate change is not only an environmental issue; it also creates evolutionary pressure. When conditions change, individuals with traits that improve survival and reproduction are more likely to pass on their alleles. Over many generations, this can change the genetic makeup of a population.

For example, if a drought becomes more common, plants with traits such as deeper roots, thicker cuticles, or reduced leaf area may survive better. These individuals are more likely to reproduce, so the alleles that help drought tolerance may become more common. This is natural selection.

However, evolution takes time. If climate change happens faster than a population can adapt, the population may decline or go extinct. This is especially important for species with long generation times or low genetic variation. Genetic diversity matters because it provides the raw material for selection.

Climate change can also cause range shifts. A species may survive by moving into a new area where conditions are suitable. But movement is not always possible because of habitat fragmentation, human development, or lack of dispersal ability. This shows a key biological idea in continuity and change: species are not fixed forever, but they are also constrained by inheritance and environment.

A classic example is the peppered moth. Although this example is usually linked to industrial pollution rather than modern climate warming, it shows how environmental change can alter selection pressures and change allele frequencies in populations. The same biological logic applies to climate-related selection. 🦋

Homeostasis, sustainability, and human impact

Homeostasis is the ability of organisms to maintain a stable internal environment. Climate change makes homeostasis harder because the external environment becomes more extreme or less predictable.

In humans, heat waves increase the risk of dehydration and overheating. The body responds by sweating and increasing skin blood flow, but these mechanisms have limits. In plants, water stress can reduce transpiration and photosynthesis, affecting growth and crop yield. In animals, changes in temperature can affect breeding success, migration, and food supply.

Climate change also links to sustainability, which means using resources in a way that does not damage the ability of future generations to meet their needs. In biology, sustainability includes preserving biodiversity, ecosystem services, and stable food webs. Examples include:

• Reducing fossil fuel use to lower $\mathrm{CO_2}$ emissions.
• Protecting forests, which store carbon and support biodiversity.
• Restoring wetlands and mangroves, which can absorb carbon and reduce flooding.
• Supporting sustainable agriculture to maintain soil health and water quality.

Biologists study these solutions because ecosystems are interconnected. If one species disappears, others may be affected. If forests are cut down, less carbon is removed from the atmosphere, and habitat loss can reduce biodiversity. This is why climate change is both a biological and a global systems issue. 🌳

Conclusion

Climate change fits perfectly within continuity and change because it shows how stable biological systems can be disrupted by long-term environmental shifts. students should remember that climate change affects homeostasis, species distribution, reproduction, and evolution. It is supported by scientific evidence and can be studied using biological data and reasoning.

The main message is that life responds to change, but not all organisms respond in the same way or at the same speed. Some adapt, some migrate, and some decline. Understanding climate change helps explain how continuity in life is maintained through change, selection, and ecological balance.

Study Notes

• Climate is the long-term pattern of weather in a region; climate change means a long-term shift in that pattern.
• Greenhouse gases such as $\mathrm{CO_2}$, $\mathrm{CH_4}$, and $\mathrm{N_2O}$ absorb infrared radiation and contribute to warming.
• Human activities increase greenhouse gas levels, especially through fossil fuel combustion and deforestation.
• Climate change affects enzymes, metabolism, reproduction, migration, flowering, and habitat suitability.
• Coral bleaching happens when warm water stresses corals and causes them to lose their symbiotic algae.
• Evidence for climate change includes temperature records, ice cores, glacier retreat, sea level rise, and species range shifts.
• In IB Biology HL, always identify variables, controls, trends, and possible biological mechanisms in data questions.
• Climate change drives natural selection, because individuals with advantageous traits are more likely to survive and reproduce.
• Genetic diversity increases the chance that a population can adapt to new conditions.
• Climate change links to homeostasis because organisms must regulate internal conditions in a more unstable environment.
• Sustainability means using resources in a way that protects biodiversity and ecosystem function for the future.
• Climate change is a clear example of continuity and change: life continues, but the conditions for life are changing.