4.4 To what extent are the water and carbon cycles linked? Flashcards
4.4 To what extent are the water and carbon cycles linked?
Key idea ➡ The water and carbon cycles are linked and interdependent.
Rapid population and economic growth (Human activities cause changes in water and carbon stores)
The rapid population and economic growth, deforestation and urbanisation in the past 100 years have modified the size of water and carbon stores and rates of transfer between stores in the water and carbon cycles.
The impact and scale of these changes is most apparent at regional and local scales.
Human activities cause changes in water and carbon stores
-Rapid population and economic growth
-Human impact on the water cycle
-Human activity and the carbon cycle
-Massive deforestation
Human impact on the water cycle (Human activities cause changes in water and carbon stores)
The human impact on the water cycle is most evident in rivers and aquifers. Rising demand for water for irrigation, agriculture and public supply, especially in arid and semi-arid environments, has created acute shortages. Colorado Basin (USA) example:
Human activity and the carbon cycle (Human activities cause changes in water and carbon stores)
Human activity and the carbon cycle alters the carbon cycle, depleting some carbon stores and increasing others. The world relies on fossil fuels for 87% of its primary energy consumption.
The exploitation of coal, oil and natural gas has removed billions of tonnes of carbon from geological store - a process that has gathered momentum in the pat 30 years with the rapid industrialisation of raw Chinese and Indian economies.
Facts and Figures: Page 131.
Massive deforestation (Human activities cause changes in water and carbon stores)
Massive deforestation has reduced the planet’s forest cover by nearly 50%. Thus the amount of carbon stored in the biosphere, and fixed by photosynthesis, gas declined steeply.
How the water and carbon cycles are inter-linked and inter-dependent
-Interlinkages in the Atmosphere
-Interlinkages in the Oceans
-Interlinkages in the Vegetation and soil
-Interlinkages in the Cryosphere
Interlinkages in the Atmosphere (How the water and carbon cycles are inter-linked and inter-dependent)
Atmospheric CO₂ has a greenhouse effect. CO₂ plays a vital role in photosynthesis by terrestrial plants and phytoplankton. Plants, which are important carbon stores, extract water from the soil and transpire it as part of the water cycle. Water is evaporated from the oceans to the atmosphere, and CO₂ is exchanged between the two stores.
Interlinkages in the Oceans (How the water and carbon cycles are inter-linked and inter-dependent)
Ocean acidity increases when exchanges of CO₂ are not in balance (i.e. inputs to the oceans from the atmosphere exceed outputs). The solubility of CO₂ in the oceans increases with lower SSTs. Atmospheric CO₂ levels influence: SSTs and the thermal expansion of the oceans; air temperatures; the melting of ice sheets and glaciers; and sea level.
Thermal expansion
An increase in the size of a substance when the temperature is increased.
Thermal expansion of the oceans
Change in matter in response to change in temperature. Oceans get warmer, they expand.
Interlinkages in the Vegetation and soil (How the water and carbon cycles are inter-linked and inter-dependent)
Water availability influences rates of photosynthesis, NPP, inputs of organic litter to soils and transpiration. The water-storage capacity of soils increases with organic content.
Temperatures and rainfall affect decomposition rates and the release of CO₂ to the atmosphere.
Interlinkages in the Cryosphere (How the water and carbon cycles are inter-linked and inter-dependent)
CO₂ levels in the atmosphere determine the intensity of the greenhouse effect and melting of ice sheets, glaciers, sea ice and permafrost. Melting exposes land and sea surfaces which absorb more solar radiation and raise temperatures further.
Permafrost melting exposes organic material to oxidation and decomposition which releases CO₂ and CH₄. Run-off, river flow and evaporation respond to temperature change.
Carbon Dioxide (CO₂)
A colourless, odourless gas produced by burning carbon and organic compounds and by respiration. It is naturally present in air and is absorbed by plants in photosynthesis. Symbol: CO₂
Methane (CH₄)
A gas found in small quantities and produced by bacteria from hydrogen and carbon dioxide. It is the simplest hydrocarbon and flammable. Symbol: CH₄
Water cycle (The impact of long-term climate change on the water and carbon cycles)
Climate change is already modifying the global water cycle. Global warming has increased evaporation and therefore the amount of water vapour in the atmosphere.
Carbon cycle (The impact of long-term climate change on the water and carbon cycles)
The impact of global climate change on the carbon cycle is complex. It depends not just on rising temperatures, but also on geographical differences in rainfall amounts.
Higher global temperatures will in general increase rates of decomposition and accelerate transfers of carbon from the biosphere and soil to the atmosphere.
Management strategies to protect the global carbon cycle
-Wetland restoration
-Afforestation
-Agricultural practices
-International agreements to reduce carbon emissions
-Cap and trade
Pages 134-135.
Management strategies to protect the global carbon cycle definition
Management strategies designed to protect the global carbon cycle as the regulator of the Earth’s climate include wetland restoration, afforestation, sustainable agricultural practices and controls on greenhouse gas emissions.
Wetlands in the carbon cycle
Wetlands include freshwater marshes, salt marshes, peatlands, floodplains and mangroves. Their common feature is a water table at or near the surface causing the ground to be permanently saturated.
Wetlands are important in the carbon cycle: they occupy 6-9% of the Earth’s land surface and contain 35% of the terrestrial carbon pool.
Wetland restoration (Management strategies to protect the global carbon cycle)
Wetlands are important in the carbon cycle. Population growth, economic development and urbanisation have placed huge pressure on wetland environments. In the lower 48 US states the wetland area has halved since 1600. Apart from loss of biodiversity and wildlife habitats, destruction of wetlands transfers huge amounts of stored CO₂ and CH₄ to the atmosphere.
Wetland restoration - Climate change (Management strategies to protect the global carbon cycle)
Climate change and the need to reduce CO₂ emissions have led to a re-evaluation of the importance of wetlands as carbon sinks. In the twentieth century, Canada’s prairie provinces lost 70% of their wetlands.
Wetland restoration - restoration programmes (Management strategies to protect the global carbon cycle)
Restoration programmes in this area have shown that wetlands can store on average 3.25 tonnes C/ha/year. Now 112,000 ha have been targeted for restoration in the Canadian prairies which should eventually sequester 364,000 tonnes C/year.
Afforestation (Management strategies to protect the global carbon cycle)
Afforestation involves planting trees in deforested areas or in areas that have never been forested. Because trees are carbon sinks, afforestation can help reduce atmospheric CO₂ levels in the medium to long term and combat climate change.
It also has other benefits such as reducing flood risks and soil erosion, and increasing biodiversity.
Agricultural practices (Management strategies to protect the global carbon cycle)
Unsustainable agricultural practices such as overcultivation, overgrazing and excessive intensification often result in soil erosion and the release of large quantities of carbon to the atmosphere.
International agreements to reduce carbon emissions (Management strategies to protect the global carbon cycle)
Climate change affects all countries. Solving the problem therefore requires international co-operation. So far, co-operation has been patchy. For variety of economic and political reasons some of the world’s largest greenhouse-gas emitters have opted to pursue narrow self-interest.
See arguments from major CO₂ emitters on Page 135.
International agreements to reduce carbon emissions - Arguments from major CO₂ emitters (Management strategies to protect the global carbon cycle)
-Countries such as China and India are still relatively poor and industrialisation, based on fossil fuel energy, is essential to raise living standards to levels comparable with those in the developed world.
-Historically, Europe and North America are largely to blame for contemporary global warming and climate change by way of industrialisation and economic development.
Cap and trade (Management strategies to protect the global carbon cycle)
Cap and trade offers an alternative, international market-based approach to limit CO₂ emissions. Under this scheme businesses are allocated an annual quota for their CO₂ emissions.
If they emit less than their quota they receive carbon credits which can be traded on international markets.Businesses that exceed their quotas must purchase additional credits or incur financial penalties.
Carbon offsets
Credits awarded to countries and companies for schemes such as afforestation, renewable energy and wetland restoration. They can be bought to compensate for excessive emissions elsewhere.
Management strategies to protect the global water cycle
-Forestry
-Water allocations
-Drainage basin planning
Forestry (Management strategies to protect the global water cycle)
Forests have a crucial role in the global water cycle which is recognised by multilateral agencies such as the United Nations (UN) and World Bank (WB). They together with other organisations and governments fund programmes to protect tropical forests.
Forestry - Programme examples (Management strategies to protect the global water cycle)
The UN’s Reducing Emissions from Deforestation and Forest Degradation (REDD) programme and the WB’s Forest Carbon Partnership Facility (FCPF) fund over 50 partner countries in Africa, Asia-Pacific and South America. Financial incentives are also provided.
Water allocations (Management strategies to protect the global water cycle)
In countries of water scarcity governments have to make difficult decisions on the allocation of water resources. Agriculture is by far the biggest consumer. Globally it accounts for 70% of water withdrawals and 90% of consumption.
Wastage of water occurs through evaporation and seepage through inefficient water management (e.g. over-irrigating crops).
Improved management techniques which minimise water losses to evaporation include mulching, zero soil disturbance and drip irrigation.
Drainage basin planning (Management strategies to protect the global water cycle)
The management of water resources is most effective at the drainage basin scale. At this scale it is feasible to adopt an integrated or holistic management approach to accommodate the often conflicting demands that impact on water quality, river flow, groundwater level, wildfire habitats, biodiversity and so on.
Page 136 for Specific targets for drainage basin planning and Surface water storage.
