Define negative feedback.

Negative feedback is a response that counteracts the original change and returns the system towards its previous state.

What is a threshold in a natural system?

A threshold is a critical point beyond which the system shifts into a new state, often abruptly and sometimes irreversibly.

What does equilibrium mean in the carbon cycle?

The stores stay roughly constant in size because inputs and outputs remain in balance, even though carbon moves continuously between them.

Explain the ice-albedo feedback.

Warming melts snow and ice to expose darker ocean or ground that reflects far less radiation, so more energy is absorbed, the surface warms further and still more ice melts.

Give approximate albedo values for fresh snow and for open ocean.

Fresh snow reflects roughly 80 to 90% of incoming radiation, while open ocean reflects less than 10%.

WJEC A-Level Geography 601-8455-3

Coastal Landscapes

Glaciated Landscapes

Topic overview The glacier as an open system Climate change and the glacier budget Glacier movement Types of ice mass and their distribution Glacial weathering and erosion processes Macro-scale erosional landforms Glacial transport and depositional landforms Fluvioglacial landforms Suites of landforms in glacial landscapes Periglacial processes and ground ice Periglacial action of water and wind Glacial change over different timescales Glacial environments and human activity

Tectonic Hazards

Topic overview The internal structure of the Earth Mechanisms of plate movement Divergent and conservative plate margins Convergent margins and subduction Hot spots and the global distribution of tectonic hazards The hazard profile and measuring magnitude Types of volcano and styles of eruption Primary volcanic hazards Secondary volcanic hazards Impacts of volcanic activity at different scales Contrasting volcanic eruptions Earthquake characteristics and seismic waves Earthquake hazards and ground behaviour Tsunami processes and impacts Contrasting earthquake events Risk, vulnerability and human factors Monitoring, prediction and warning Mitigation, response and the hazard management cycle

Changing Places

Topic overview What gives a place its character Flows and connections that shape places Meaning, perception and attachment to place How places are represented Economic restructuring and the Clark Fisher model Deindustrialisation and social inequality The service economy and its impacts The knowledge economy and clusters Rebranding rural places Managing change in rural places Rebranding urban places Managing change in urban places Comparing a home place with a contrasting place How place change affects people's lives

Water and Carbon Cycles

Topic overview The water cycle as a global system and mass balance Global water stores and residence times Cryospheric processes and sea-level change Drainage basin inputs, stores and outputs Flows within the drainage basin River regimes and their controls Storm hydrographs and hydrograph shape Air uplift, cloud formation and precipitation Excess runoff and flooding Deficit in the water cycle and aquifer recharge The global carbon cycle and its stores Carbon pathways between land and the atmosphere Carbon transfers involving the oceans Carbon stores in biomes and land-use change Changing carbon stores in peatlands Rising atmospheric carbon and its impacts Feedback within and between the water and carbon cycles

Global Migration

Topic overview Globalisation and a shrinking world Classifying and mapping migration Causes of international economic migration Consequences and management of economic migration Refugee movements and internal displacement Rural-urban migration in developing countries Superpowers and global hub cities Migration policy and public debate in the UK Managing refugee crises Informal settlements in developing cities

Global Governance of the Oceans

Topic overview Supranational institutions and global governance Laws and agreements governing the oceans Strategic value of the oceans and maritime security Shipping, cables and illicit flows Sovereignty over ocean resources Managing marine environments Ocean pollution and its management Governance across scales: an ocean case study

EcosystemsContemporary theme

Topic overview The value of ecosystems to people The distribution of global biomes Ecosystem structure, energy flow and productivity Nutrient cycling in contrasting biomes Measuring and threatening biodiversity Conserving biodiversity Succession and local ecosystems The Arctic tundra biome Sustainable use of the Arctic tundra

Economic Growth and Challenge: IndiaContemporary theme

Topic overview India's relief, drainage and climate India's population, society and governance India's resources, hazards and economic geography India's global role and economic growth Environmental pressures of India's growth Sustainable development strategies in India

Economic Growth and Challenge: ChinaContemporary theme

Topic overview China's relief, drainage and climate China's population, society and governance China's resources, hazards and economic geography China's global role and economic growth Environmental pressures of China's growth Sustainable development strategies in China

Development in an African ContextContemporary theme

Topic overview Defining and measuring development Physical factors influencing development Economic factors influencing development Political, social and cultural factors in development The environmental cost of development Desertification Strategies to promote development

Energy Challenges and DilemmasContemporary theme

Topic overview Classifying and distributing energy resources Physical factors in energy supply The changing demand for energy Managing oil and gas globally Problems of extraction, transport and use Energy mixes and development Sustainable solutions to energy demand

Weather and ClimateContemporary theme

Topic overview Structure of the atmosphere and the heat budget Global atmospheric and oceanic circulation The world's major climate types Weather and climate of Wales and the UK Extreme weather and ENSO Hazards of low and high pressure systems Urban climates and air quality People, climate and the future

Fieldwork and Geographical Skills

Topic overview The six-stage enquiry process Sampling and data collection Presenting geographical data Statistical analysis of geographical data Fieldwork techniques and apparatus Map skills: grid references, latitude and longitude, scale and direction

Key Concepts in Geography

Topic overview Systems, equilibrium and feedback Causality, interdependence and mitigation Resilience, risk and sustainability Place, space, scale and representation

Water and Carbon Cycles

Feedback within and between the water and carbon cycles

2 things to know
A2 Unit 3

Overview

Positive feedback, negative feedback and threshold in a natural system.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why does cloud cover make the net direction of feedback uncertain?

Key term

Define positive feedback.

Questions from this subtopic

Each one with the model answer underneath.

1
Define positive feedback.
Model answer
Positive feedback is a response that amplifies the original change and drives the system further from where it started.
2
Define negative feedback.
Model answer
Negative feedback is a response that counteracts the original change and returns the system towards its previous state.
3
What is a threshold in a natural system?
Model answer
A threshold is a critical point beyond which the system shifts into a new state, often abruptly and sometimes irreversibly.
4
What does equilibrium mean in the carbon cycle?
Model answer
The stores stay roughly constant in size because inputs and outputs remain in balance, even though carbon moves continuously between them.
5
Explain the ice-albedo feedback.
Model answer
Warming melts snow and ice to expose darker ocean or ground that reflects far less radiation, so more energy is absorbed, the surface warms further and still more ice melts.
6
Give approximate albedo values for fresh snow and for open ocean.
Model answer
Fresh snow reflects roughly 80 to 90% of incoming radiation, while open ocean reflects less than 10%.

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