Evaluate the impact of human activities on atmospheric composition and the consequences for ecosystems [9 marks]

Indicative Content	Guidance
Human-induced changes: Emission of greenhouse gases (CO₂ / methane) from industrial activities Release of pollutants affecting air quality (nitrogen oxides / sulfur dioxide) Alterations in ozone levels due to human-made substances (CFCs) Consequences for ecosystems: Impact on climate patterns and global temperatures Changes in precipitation patterns affecting ecosystems Acid rain formation and its effects on soil and aquatic environments Influence on biodiversity and species distribution Case Studies and examples: Ozone depletion: Human activity → widespread use of CFCs in refrigeration / aerosol propellants Atmospheric consequence → thinning of the ozone layer, particularly over Antarctica Ecosystem impact → increased UV radiation reaching Earth's surface → harming marine phytoplankton / disrupting food chains / contributing to skin cancers in humans Industrial emissions and air quality in megacities: Human activity → massive industrial emissions / vehicular pollution in megacities Atmospheric consequence → elevated concentrations of nitrogen oxides / particulate matter Ecosystem impact → degradation of air quality → leading to respiratory issues in human populations (e.g. in cities like Beijing / Delhi) Interconnectedness of systems: Discuss the interconnected nature of the atmosphere and ecosystems Recognition of feedback loops / compounding effects of atmospheric changes on ecosystems Evaluation of human impact: Assessment of the scale / magnitude of human-induced changes Consideration of the time frame for observable consequences Discuss global versus local impacts on ecosystems Importance of policy / education: Role of international agreements / policies in addressing atmospheric concerns Significance of public awareness / education in reducing harmful activities	You will always have to answer two 9 mark questions from Section B in your IB ESS SL Paper 2 exam This is a 'level of response' answer. The examiner will award you a combined mark out of 9 for knowledge, application, analysis and evaluation ‘Evaluate’ (for 9 marks) requires: Knowledge of concepts, principles and models Application to the context using relevant and focused examples Analysis showing logical and coherent chains of reasoning of a range of issues Evaluation showing critical thinking linked to the context Depth is more important than breadth It is sensible to discuss two or three main points but to apply, analyse and evaluate them fully For top-level evaluation, informed judgement is required This can be demonstrated in a conclusion that synthesises and weighs up the arguments to form a supported answer to the question
Model Answer
The Earth's atmosphere is a delicate balance of gases crucial for sustaining life, but it has undergone significant changes, particularly in the last few hundred years, due to human activities. Human activities have significantly altered atmospheric composition, leading to consequences for various ecosystems. The release of greenhouse gases, such as carbon dioxide, from burning fossil fuels, has contributed to global warming, impacting ecosystems like coral reefs. Increased sea temperatures due to climate change have triggered coral bleaching, stressing the symbiotic relationship between corals and algae [K]. The Great Barrier Reef in Australia, for example, has experienced extensive bleaching events, threatening the biodiversity it supports [Ap]. Another example is the impact of acid rain on forest ecosystems. Emissions of sulfur dioxide and nitrogen oxides from industrial activities and combustion of fossil fuels lead to acid rain formation. This can damage forests, particularly in Europe and North America [K]. For example, the Black Forest in Germany has suffered significant damage, with soil acidification affecting nutrient uptake by trees [Ap]. The weakened trees are more susceptible to diseases and extreme weather events, disrupting the delicate balance of these ecosystems [An]. While assessing the human impact on atmospheric composition, it is essential to consider the interconnectedness of systems. Feedback loops can amplify the consequences, highlighting the urgency for comprehensive and immediate action to stop these tipping points being reached [An]. For example, rising greenhouse gas emissions are leading to disproportionate warming in the Arctic. Melting of sea ice not only causes a loss of habitat but also reduces reflectivity, causing the ocean to absorb more heat, creating a feedback loop. This warming accelerates permafrost thaw, releasing stored carbon and methane, intensifying the greenhouse effect globally [Ap]. In conclusion, the impact of human activities on atmospheric composition is negatively affecting many ecosystems. In evaluating these examples, it is clear that human-induced atmospheric changes have complex, knock-on effects on ecosystems [An]. Species interconnectedness within ecosystems makes their biodiversity vulnerable to these alterations in atmospheric composition. Urgent mitigation efforts are essential to preserve these delicate balances and ensure ecosystems can be resilient in the face of ongoing human activities. We need to take a holistic approach that balances current societal needs with preserving the planet's life-supporting systems [E].
Commentary
This answer is an example - yours may be different The answer evaluates two major changes to the atmosphere and the effects of these, as well as considering how these effects can multiply in some circumstances The answer contains specific examples to show how particular ecosystems are being affected The response is annotated to show where the skills of knowledge (K), application (Ap), analysis (An) and evaluation (E) have been demonstrated

Introduction to the Atmosphere (SL IB Environmental Systems & Societies (ESS))

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