Climate change (5.12, 5.13, 5.14, 5.15, 5.16)
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Atmospheric concentrations have varied widely throughout Earth’s history.
data from direct measurements and ancient ice core gas bubbles show two distinct timelines:
- Short-term: an annual cycle where Northern Hemisphere summer photosynthesis draws down while winter respiration and decay cause it to peak in May.
- Long-term: historical variations occurred naturally via volcanic activity, never exceeding 300 for millennia. However, modern fossil fuel combustion and deforestation have shattered the pre-industrial baseline of 280 surging past 420 by 2026.
Scientists collect temperature data from weather stations, ocean measurements and satellites.
Data have shown that global average temperatures have increased over recent decades. Although some of the data show a decline in some years, long-term trends are more important than individual yearly changes.
Limitations of these measurements are:
- Older records have fewer measurements.
- Urban areas may be warmer due to the urban heat island effect.
- Data must be corrected and combined from many locations
Data show that atmospheric carbon dioxide concentration and global temperature have changed together over thousands of years.
There is a positive correlation between levels and global temperature. This does not prove one causes the other. Factors such as volcanic activity and changes in solar radiation have an influence.
There is however evidence for a causal relationship because carbon dioxide is a greenhouse gas. Increasing concentrations causes increased absorption of outgoing infrared radiation. This strengthens the greenhouse effect, causing global temperatures to rise.
Peat is an accumulation of partially decayed organic matter formed in waterlogged, acidic, anaerobic conditions. It builds up with deeper layers representing older time periods.
Pollen grains can be preserved in peat and provide evidence for climate change.
Plants have specific climatic requirements so pollen composition provides evidence of past climates. For example, increased presence of pollen from warm-adapted plants suggests warmer conditions.
Limitations: pollen may travel from other areas, and identification requires expertise.
Dendrochronology is the study of tree rings to investigate past climates.
Trees produce a new growth ring each year, allowing scientists to estimate the age of trees and reconstruct past environmental conditions. Wider rings usually indicate favourable conditions, such as warmer temperatures and sufficient water, while narrower rings suggest stressful conditions such as drought or cold periods.
It is important to note there are limitations to dendrochronology – tree growth can also be affected by factors such as disease, competition, and soil conditions, so ring width is not controlled by climate alone.
Anthropogenic climate change occurs when human activities increase greenhouse gas concentrations, thereby enhancing the greenhouse effect and causing global warming.
- Carbon dioxide increase (): released by fossil fuel combustion and biomass burning. Deforestation increases levels by reducing the number of trees available to remove through photosynthesis.
- Methane increase (): released from livestock digestion, rice farming and landfill decomposition. Methane is a more powerful greenhouse gas than , so smaller amounts can have a significant warming effect.
The greenhouse effect is a natural process where greenhouse gases in the atmosphere absorb and re-radiate infrared radiation, reducing heat loss from Earth and keeping the planet warm enough for life.
- High-energy, short-wavelength light from the sun passes through greenhouse gases to warm Earth’s surface.
- The warmed Earth re-radiates this energy upward as lower-energy, long-wavelength infrared radiation.
- Greenhouse gases such as carbon dioxide () and methane () absorb this infrared radiation and emit it in all directions, including back towards Earth. An increase in these greenhouse gases results in atmospheric warming.
Scientists use historical datasets to predict future global warming trends:
- Extrapolation – mathematically extending a known, verified trend line of past data forward into an unmeasured future.
- Climate Models – climate models use computer simulations that combine data such as greenhouse gas emissions, atmospheric temperatures, ocean temperatures and other climate factors. These models predict possible future outcomes, including temperature rise and sea-level changes.
Predictions help scientists and governments plan strategies to reduce greenhouse gas emissions and adapt to climate impacts.
Limitations of models of future climate change:
- Uncertainty: models require assumptions about future greenhouse gas emissions, population growth and human behaviour.
- Limited data: past climate records may be incomplete.
- Complex interactions: climate systems involve many interacting factors, such as clouds, oceans and ice sheets, which are difficult to model accurately.
- Different predictions: models may produce different outcomes because they use different assumptions and methods.
Climate change alters global rainfall patterns, causing some regions to become wetter and others drier.
These changes affect plants and animals by:
- Reducing water availability for growth and reproduction.
- Increasing drought stress and wildfires.
- Increasing flooding, which can destroy habitats.
- Changing ecosystem productivity and food availability.
Species unable to tolerate new conditions may decline or become locally extinct.
Climate change is altering the timing of seasonal events (phenology).
Examples of altered phenology include:
- Earlier flowering of plants.
- Earlier emergence of insects.
- Earlier bird migration and breeding.
- Longer growing seasons.
If species respond at different rates, seasonal mismatches can occur. For example, chicks may hatch after their main food source has already peaked, reducing survival and reproductive success.
Global warming forces plants and animals to shift their geographic ranges to maintain their niches.
Some of the impacts of climate change are:
- Species are actively migrating toward higher latitudes (the poles) or higher altitudes (up mountains) where conditions match their physiological tolerances.
- Polar species or those at mountain summits have nowhere left to migrate as glaciers and polar ice are melting.
- Slow-moving or immobile species (like slow-growing trees) cannot migrate fast enough to escape climate shifts, leading to localised extinctions.
Temperature influences the rate of enzyme-controlled reactions, so climate change can alter the development and life cycles of many organisms.
- Altered temperatures and rainfall patterns disrupt the timing of biological growth and reproduction.
- Higher ambient temperatures speed up enzyme-controlled metabolic pathways, causing accelerated development in ectotherms (like insects).
- Phenological shifts occur when matching species drift apart. For example, warmth prompts plants to flower earlier, meaning insect pollinators emerge out of sync.
Changes in timing may disrupt predator–prey interactions, pollination and food availability, reducing survival and reproductive success.
Temperature affects the speed at which molecules move and, therefore, the rate at which enzyme and substrate molecules collide.
Enzymes have an optimum temperature, where they catalyse reactions fastest. This is the temperature at which the maximum number of enzyme–substrate complexes form.
At low temperatures, molecules have less kinetic energy and move more slowly. This leads to fewer successful collisions between enzymes and substrates. As a result, fewer enzyme–substrate complexes form and the reaction rate is slower.
Higher temperatures provide more kinetic energy. This results in more frequent and successful collisions between enzymes and substrates, accelerating the reaction.
Beyond the optimum temperature, too much kinetic energy breaks the hydrogen and ionic bonds that maintain the enzyme’s tertiary structure and shape the active site. The enzyme is said to be denatured. If the enzyme cannot bind the substrate, it cannot catalyse the reaction and the reaction rate drops sharply.
Denaturation is often irreversible.
The temperature coefficient is a measure of the change in the rate of a reaction after increasing the temperature by .
is calculated using the formula:
where:
is the initial temperature.
For most enzyme-catalysed reactions, values typically range between 2 and 3. This means the rate of reaction roughly doubles or triples with every rise in temperature.
The relationship does not apply outside of an enzyme’s optimum temperature range.
