Introduction to Climate Change
Welcome to one of the most important chapters in your A Level Biology course! In this section of Unit 4, we are going to look at the "detective work" biologists and climatologists do. We will explore how we know the climate is changing, why it is happening, and what it means for the living things on our planet. Don't worry if the data seems overwhelming at first—we will break it down piece by piece.
1. Evidence for Climate Change
Scientists don't just "guess" that the Earth is getting warmer; they use several different types of evidence to look back into the past. Here are the four key methods you need to know for your exam:
A. Temperature Records
Since about 1850, humans have been using thermometers to keep instrumental records of the temperature. These records show a clear upward trend in global temperatures over the last century. While early records might be less reliable than modern satellite data, the overall pattern is undeniable.
B. Carbon Dioxide (\(CO_2\)) Records
By analyzing ice cores (long cylinders of ice drilled from glaciers), scientists can trap ancient bubbles of air. This allows them to measure exactly how much \(CO_2\) was in the atmosphere thousands of years ago. Modern data from places like Mauna Loa in Hawaii shows that \(CO_2\) levels have spiked significantly since the Industrial Revolution.
C. Dendrochronology (Tree Rings)
Most trees grow a new ring of xylem every year.
• Wide rings indicate a warm, wet year (better growing conditions).
• Narrow rings indicate a cold or dry year.
By looking at the thickness of these rings in very old trees or preserved wood, we can "read" the climate history of a specific area going back hundreds or even thousands of years.
D. Pollen in Peat Bogs
Peat bogs are amazing at preserving things because they are acidic and anaerobic (low in oxygen), which slows down decomposition. Pollen grains are tough and have distinct shapes for different species.
How it works: Scientists take a core sample of the peat. Because peat builds up in layers, the deeper layers are older. If we find pollen from plants that only grow in warm climates in a specific layer, we know that the climate was warm when that layer was formed.
Quick Review: Remember that pollen tells us about the type of plants present, while tree rings tell us about the rate of growth.
2. The Greenhouse Effect and Gases
The Earth stays warm because of the greenhouse effect. Short-wave radiation from the sun hits the Earth; some is reflected back as long-wave infrared radiation. Greenhouse gases trap this infrared radiation in the atmosphere, keeping the planet warm enough for life.
The Problem: Human activity (burning fossil fuels and farming) has increased the concentration of these gases, leading to the enhanced greenhouse effect and global warming.
• Carbon Dioxide (\(CO_2\)): Released by burning fossil fuels and respiration.
• Methane (\(CH_4\)): Released by cattle farming, rice paddies, and decaying waste in landfill sites.
3. The Carbon Cycle
The carbon cycle is the movement of carbon between the atmosphere, living organisms, and the Earth.
• Photosynthesis: Removes \(CO_2\) from the atmosphere.
• Respiration: Adds \(CO_2\) to the atmosphere.
• Combustion: Burning wood or fossil fuels adds \(CO_2\).
• Decomposition: Microorganisms break down dead organic matter, releasing \(CO_2\) (see Topic 6 for more on decomposition).
4. Climate Models and Their Limitations
Scientists use powerful computers to create models to predict future climate change. These models use current data on \(CO_2\) levels, population growth, and energy use.
Limitations of Models:
1. Complexity: The Earth's climate system is incredibly complex with many interacting factors (like clouds and ocean currents).
2. Unknown Future: We don't know how much human behavior will change (e.g., will we stop using coal tomorrow?).
3. Data Gaps: We don't have perfect historical data for every part of the world.
5. Effects on Plants and Animals
Climate change isn't just about things getting hotter; it changes how life functions.
• Distribution: As areas warm up, species may move toward the poles or higher up mountains to find their "ideal" temperature.
• Life Cycles (Phenology): Many organisms use temperature as a cue for migration, flowering, or hatching. If a bird hatches its eggs based on day length, but the caterpillars it eats emerge earlier due to temperature, the chicks may starve.
• Natural Selection: Changes in the environment lead to changes in allele frequency. If a species cannot adapt or move quickly enough, it may face extinction.
6. Temperature and Enzyme Activity
This is a favorite topic for exam questions! Most biological processes are controlled by enzymes. As temperature increases, the kinetic energy of molecules increases, leading to more frequent successful collisions between enzymes and substrates.
The Temperature Coefficient (\(Q_{10}\))
The \(Q_{10}\) value shows how much the rate of a reaction increases when the temperature is raised by \(10 ^\circ C\).
The formula is:
\(Q_{10} = \frac{\text{Rate at } (T + 10) ^\circ C}{\text{Rate at } T ^\circ C}\)
For most biological reactions between \(0 ^\circ C\) and \(40 ^\circ C\), the \(Q_{10}\) is approximately 2. This means the reaction rate doubles for every \(10 ^\circ C\) rise.
Core Practical 12: You may be asked about investigating the effect of temperature on the development of organisms (like seedling growth or brine shrimp hatching). Remember to control other variables like light or pH to ensure a valid result!
7. Solutions: Reforestation and Biofuels
To combat climate change, we need to reduce the amount of \(CO_2\) in the atmosphere.
Reforestation: Planting more trees increases the rate of photosynthesis, which acts as a "carbon sink," pulling \(CO_2\) out of the air and storing it in biomass.
Biofuels: These are fuels made from biomass (like sugar cane or vegetable oil). They are often considered carbon neutral because the \(CO_2\) released when they are burned is roughly equal to the \(CO_2\) the plant absorbed while growing.
Note: They aren't perfectly carbon neutral because of the energy needed to harvest and transport them!
Key Takeaway Summary:
• Evidence includes temperature records, ice cores, tree rings, and pollen.
• Increased greenhouse gases (\(CO_2\) and \(CH_4\)) lead to global warming.
• Temperature affects enzyme kinetics (\(Q_{10}\)) and alters species distribution.
• Models help us predict the future but are limited by complexity and uncertainty.