Climate Change 🌍

students, climate change is one of the most important examples of continuity and change in biology because it shows how living things and ecosystems can stay similar in some ways while also changing over time. In IB Biology SL, this topic connects ideas from molecular genetics, inheritance, homeostasis, and sustainability. The big question is simple but powerful: how do changing environmental conditions affect life on Earth, and how do organisms respond? 🌱

In this lesson, you will learn to explain the main ideas and terms linked to climate change, use biological reasoning to interpret its effects, and connect it to the wider theme of continuity and change. By the end, you should be able to describe how climate change influences species, populations, and ecosystems, and why it matters for the future of biodiversity and human life.

What climate change means

Climate change refers to long-term changes in average weather patterns, especially temperature, rainfall, wind, and the frequency of extreme events. A key idea is that climate is different from weather. Weather describes short-term conditions, such as today’s rain or tomorrow’s heat. Climate describes patterns over many years or decades.

The current climate change issue is mainly linked to a rise in global average temperature, often called global warming. This warming is strongly associated with increased levels of greenhouse gases in the atmosphere, especially $\text{CO}_2$, methane, and nitrous oxide. These gases absorb and re-radiate heat, trapping more energy in the Earth system. This process is known as the greenhouse effect.

The greenhouse effect is natural and necessary. Without it, Earth would be too cold for most life. The problem is that human activities have strengthened it. Burning fossil fuels, such as coal, oil, and natural gas, releases large amounts of $\text{CO}_2$. Deforestation also increases atmospheric $\text{CO}_2$ because fewer trees are available to remove it through photosynthesis 🌳.

Why climate change matters in biology

Climate change is not only an environmental issue; it is a biological issue because all organisms depend on suitable conditions for survival, growth, and reproduction. When temperature, water availability, or seasonal timing changes, the biology of organisms can be affected at many levels.

For example, enzymes work best within a narrow temperature range. If temperature changes too much, enzyme activity may decrease, which can slow metabolism. This affects processes such as respiration, digestion, and photosynthesis. Plants may close stomata to reduce water loss in hotter, drier conditions, but this also reduces carbon dioxide intake and can lower photosynthesis rates. Small changes in environment can therefore cause major changes in biological function.

Climate change can also alter the distribution of species. Some organisms may move to cooler regions or higher altitudes. Others may not be able to move quickly enough, especially if they are specialized or have limited dispersal abilities. This can lead to local extinction, changes in community structure, and loss of biodiversity.

Biological responses: homeostasis, adaptation, and selection

students, one way to understand climate change is through homeostasis, which is the maintenance of stable internal conditions in an organism. Many organisms have mechanisms to control body temperature, water balance, and salt concentration. However, extreme or rapid climate changes can overwhelm these systems.

For example, humans regulate body temperature using sweating and changes in blood flow to the skin. But in very hot conditions, especially during heat waves, the body can struggle to lose enough heat. In plants, drought stress can reduce water uptake, causing wilting and reduced growth. If climate change increases the frequency of heat waves and droughts, homeostasis becomes harder to maintain.

Climate change also affects natural selection. In a changing environment, individuals with traits that help them survive and reproduce are more likely to pass on those traits. Over time, populations may become better adapted to new conditions. This is an example of evolution by natural selection.

A simple example is a population of insects exposed to warmer temperatures. Individuals that tolerate heat better may survive and reproduce more successfully. If that trait has a genetic basis, the frequency of the alleles associated with heat tolerance may increase in the population. This is continuity and change in action: the species continues, but the genetic composition of the population changes over generations.

Evidence and examples from ecosystems

Scientists study climate change using many types of evidence. Long-term temperature records, ice cores, tree rings, satellite data, and changes in species distributions all provide information. In biology, evidence from living systems is especially important.

One well-known example is coral bleaching. Corals have a symbiotic relationship with photosynthetic algae called zooxanthellae. When ocean temperatures rise, corals may expel these algae. Without them, corals lose a major source of nutrients and may turn white, a process called bleaching. If stressful conditions continue, the coral may die. This affects entire reef ecosystems because reefs provide habitat for many species.

Another example is the timing of seasonal events, known as phenology. Flowering, migration, breeding, and hibernation are often controlled by temperature and day length. Climate change can shift these events. If insects emerge earlier but birds do not, food availability may no longer match breeding time. This mismatch can reduce survival and reproductive success.

Climate change can also affect disease patterns. Warmer temperatures may allow some disease vectors, such as mosquitoes, to survive in new regions. This can increase the range of diseases and affect both human health and wildlife populations. The biological consequence is not just warmer weather, but altered interactions between organisms.

Connecting climate change to continuity and change

The topic of continuity and change focuses on how biological systems persist and how they transform over time. Climate change fits this theme perfectly.

At the molecular level, genes and alleles remain part of the continuity of life because DNA is passed from one generation to the next. At the same time, environmental pressure can shift which alleles are more common through selection. Inheritance provides continuity, while adaptation provides change.

At the cellular level, organisms maintain homeostasis to keep internal conditions stable, even as the external environment changes. But if the environment changes too rapidly, cells and tissues may be damaged. This shows the tension between stability and change.

At the ecosystem level, climate change can alter food webs, migration routes, species interactions, and habitat availability. Some species may adapt, some may migrate, and some may go extinct. The ecosystem continues, but its structure changes.

This is why climate change is a strong example of continuity and change in IB Biology SL. It shows that life is not static. Living systems respond to pressure, and those responses can be seen across scales, from genes to ecosystems 🌎.

Using IB Biology SL reasoning on climate change

In IB Biology SL, you may be asked to interpret data, explain mechanisms, or predict outcomes. Here is the kind of reasoning expected.

If a graph shows rising atmospheric $\text{CO}_2$ levels and increasing global temperature, you should describe the correlation and explain the likely biological cause. More $\text{CO}_2$ enhances the greenhouse effect, which increases average temperature. Then you should link that to biological impacts, such as altered enzyme activity, water stress in plants, or shifts in species ranges.

If a question asks how climate change affects biodiversity, remember that biodiversity can decrease when habitats are lost, food webs are disrupted, or species fail to adapt fast enough. You may mention that populations with low genetic variation are less likely to survive rapid environmental change because there may be fewer alleles that help individuals cope with new conditions.

If asked about procedures or investigations, you might explain how scientists collect data over time, compare populations in different environments, or use models to predict future changes. Evidence should be described clearly and linked to the biological conclusion.

Real-world actions and sustainability

Climate change also connects to sustainability, which means using resources in ways that allow ecosystems and human societies to continue in the long term. In biology, sustainability is important because ecosystems provide food, oxygen, water regulation, pollination, and climate regulation.

Actions that reduce climate change include lowering fossil fuel use, improving energy efficiency, protecting forests, restoring wetlands, and supporting sustainable agriculture. Forests and wetlands are especially important because they act as carbon sinks, storing carbon and helping reduce atmospheric $\text{CO}_2$.

students, the key biological idea is that healthy ecosystems are more resilient. Resilience is the ability to recover after disturbance. Ecosystems with high biodiversity often have greater resilience because different species may fill similar roles, helping the system continue functioning even when conditions change.

Conclusion

Climate change is a major biological challenge and a clear example of continuity and change. It affects enzyme function, homeostasis, reproduction, inheritance, natural selection, and ecosystem stability. Some organisms respond by adapting or moving, while others decline or disappear. The lesson shows that living systems are dynamic and interconnected, and that changes in climate can reshape life at every level. Understanding climate change helps you see how biology explains both the persistence of life and the forces that transform it over time.

Study Notes

• Climate is the long-term pattern of weather; weather is short-term atmospheric conditions.
• Climate change is mainly linked to increased greenhouse gases such as $\text{CO}_2$, methane, and nitrous oxide.
• Human activities like burning fossil fuels and deforestation increase atmospheric $\text{CO}_2$.
• The greenhouse effect is natural, but extra greenhouse gases strengthen it and raise global temperatures.
• Climate change affects enzyme activity, photosynthesis, respiration, water balance, and homeostasis.
• Natural selection may favor individuals with traits that help them survive new conditions.
• Genetic variation matters because populations with more variation have a better chance of adapting.
• Examples include coral bleaching, changed migration times, drought stress in plants, and shifting species ranges.
• Climate change can reduce biodiversity by causing habitat loss, mismatched timing, and extinction.
• The topic links continuity and change because genes are inherited continuously while populations and ecosystems change over time.
• Sustainability involves using resources so ecosystems can continue functioning in the future.