4.4 To What Extent are the Water and Carbon Cycles Linked? Flashcards
How are the water and carbon cycles linked?
Increasing levels of CO2 in the atmosphere drive global warming and highlight the linkages between the water and carbon cycles.
What human activities affect water and carbon stores?
Rapid population and economic growth, deforestation and urbanisations 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.
Where is the human impact on the water cycle most evident?
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 in the Colorado Basin in the southwest USA, surface supplies have diminished as more water is abstracted from rivers, and huge amounts are evaporated from reservoirs like Lake Mead and Lake Powell Elsewhere, the quality of fresh water resources has declined Over pumping of aquifers in the coastal regions of Bangladesh has led to incursions of salt water, often making the water unfit for irrigation and drinking
What is the impact of human activity on the water cycle?
Compared to natural ecosystems, human activities such as deforestation and urbanisation reduce evapotranspiration and therefore precipitation; increased surface run-off; decreased throughflow and lower water tables. In Amazonia, forests are a key component of the water cycle, transferring water to the atmosphere by evapotranspiration, which is then returned through precipitation, in places, deforestation has broken this cycle, causing climates to dry out and preventing regeneration of the forest.
How is human activity impacting the carbon cycle?
Human activity is also altering the carbon cycle depleting some carbon stores and increasing others. The world relies on fossil fuels for 84 per cent of its primary energy consumption. The exploitation of coal, oil and natural gas has removed billions of tonnes of carbon from geological stores-a process that has gathered momentum in the past 30 years with the rapid industrialisation of Chinese and Indian economies. Currently around 8 billion tonnes of carbon a year are transferred to the atmosphere by burning fossil fuels. In addition, land change (mainly deforestation) transfers approximately 1 billion tonnes of carbon to the atmosphere annually. The additional carbon is stored primarily as atmospheric CO2 where its concentration increases year-by-year. Around 2.5 million tonnes is absorbed by the oceans, and a similar amount by the biosphere.
How does deforestation affect the water cycle in Amazonia?
Massive deforestation has reduced the planet’s forest cover in historic times by nearly 50 per cent. Thus the amount of carbon stored in the biosphere, and fixed by photosynthesis, has declined steeply.
What role do phytoplankton play in the carbon cycle?
Even more significant is photosynthesis by phytoplankton in the oceans Ultimately phytoplankton absorb more than half the CO, from burning fossil fuels significantly more than the tropical forests. Acidification of the oceans threatens this vital biological carbon store as well as adversely affecting marine life. Soil is another important carbon store which is being degraded by erosion caused by deforestation and agricultural mismanagement. Carbon stores in wetlands, drained for cultivation and urban development, have also been depleted as they dry out and are oxidised.
How are the carbon and water cycles linked in the cryosphere?
CO2 levels in the atmosphere determine the intensity of the greenhouse effect and the 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.
How are the water and carbon cycles linked in the atmosphere?
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.
How are the carbon and water cycles linked in the oceans?
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 SST’s . Atmospheric CO2 levels influence SST’s and the thermal expansion of the oceans; air temperatures; the melting of ice sheets and glaciers and sea ice.
How are the water and carbon cycles linked in vegetation and soil?
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.
What is the impact of long term climate change on the water cycle?
Climate change is already modifying the global water cycle. Global warming has increased evaporation and therefore the amount of water vapour in the atmosphere. More vapour which is a natural GHG, has a feedback effect helping to raise global temperatures, increase evaporation and precipitation. Meanwhile increased precipitation will result in higher run-off in the water cycle and greater flood risks Water vapour is also a source of energy in the atmosphere, releasing latent heat on condensation. With more energy in the atmosphere extreme weather events such as hurricanes and mid-latitude storms become more powerful and more frequent
Global warming is accelerating the melting of glaciers, ice sheets like Greenland and permafrost in the Arctic tundra. Thus water storage in the cryosphere shrinks, as water is transferred to the oceans and atmosphere
What is the impact of long term climate change on the carbon cycle?
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. However, in the humid tropics climate change may increase aridity and threaten the extent of forests. As forests are replaced by grasslands the amount of carbon stored in tropical biomes will diminish. In contrast in high latitudes, global warming will allow the boreal forests of Siberia and Canada and Alaska to expand polewards
Carbon frozen in the permafrost of the tundra is being released as temperatures rise above freezing and allow oxidation and decomposition of vast peat stores. Meanwhile, acidification of the oceans through the absorption of excess CO, from the atmosphere reduces photosynthesis by phytoplankton, limiting the capacity of the oceans to store carbon. Thus long-term climate change will probably see an increase in carbon stored in the atmosphere, a decrease in carbon stored in the biosphere and possibly a similar decrease in the ocean carbon stores. Movement of carbon into and out of the atmosphere will vary regionally, depending on changes in rates of photosynthesis, decomposition and respiration.
What management strategies protect the global carbon cycle?
Management strategies designed to protect the carbon cycle as the regulator of the Earth’s climate include wetland restoration, afforestation, sustainable practices and controls on greenhouse gas emissions
What is the importance of wetland restoration for 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 cent of the Earth’s land surface and contain 35 per cent of the terrestrial carbon pool.
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
However, 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 cent of their wetlands. 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.
The need for protection of wetlands as wildlife habitats as well as carbon stores is reflected in management initiatives such as the International Convention on Westland (Ramsar) and European Union Habitats Directive. In the UK up to 400 ha of grade 1 farmland in east Cambridgeshire is currently being converted back to wetland. This project assisted the UK government in meeting its target of restoring 500 ha of wetland by 2020. A similar scheme is underway in Somerset.
Restoration focuses on raising local water tables to re-create waterlogged conditions. Wetlands on floodplains for example can be reconnected to river by the removal of flood embankments and controlled floods. Coastal areas of reclaimed marshland used for farming can be restored by breaching sea defences. Elsewhere water levels can be maintained at artificially high levels by diverting or blocking drainage ditches and installing sluice gates
What is afforestation?
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 CO, 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 Protecting tropical forests from loggers, farmers and miners is an inexpensive way of curbing greenhouse gas emissions. The UN’s Reducing Emissions from Deforestation and Forest Degradation (REDD) scheme incentivises developing countries to conserve their rainforests by placing a monetary value on forest conservation. Several projects are already well established such as those in Amazonia (Puras, Russas Valparaiso) and the Lower Mississippi
In China a massive government-sponsored afforestation project began in 1978, it aims to afforest 400,000 km (an area roughly the size of Spain) by 2050. In the decade 2000-09, 30.000 km were successfully planted with non-native, fast-growing species such as poplar and birch However, the project has a wider purpose to combat desertification and land degradation in the vast semi- arid expanses of northern China
How are agricultural practices a management strategy for the 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. Intensive livestock farming produces 100 million tonnes/year of CH, a potent greenhouse gas. Almost as important are CH4 emissions from flooded (padi) rice fields and from the uncontrolled decomposition of manure.
What international agreement aimed to reduce global CO2 emissions?
Climate change affects all countries. Solving the problem therefore requires international co-operation. So far, co-operation has been patchy. For a variety of economic and political reasons some of the world’s largest greenhouse-gas emitters have opted to pursue narrow self-interest.
Until recently the only significant international agreement to tackle climate change has been the Kyoto Protocol (1997). Under Kyoto, most rich countries agreed to legally binding reductions in their CO2 emissions, though controversially, developing countries, and some of the biggest polluters (eg China and India), were exempted. Also, several rich countries, notably the USA and Australia, refused to ratify the treaty. Kyoto expired in 2012. After several rounds of negotiation, a new international agreement was finally reached at the Paris Climate Convention in 2015 with implementation from 2020. The Paris Agreement aims to reduce global CO2 emissions below 60 per cent of 2010 levels by 2050, and keep global warming below 2°C (but ideally by 1.5 °C). However, countries will set their own voluntary targets. These are not legally binding and a timetable for implementing them has yet to be agreed. Meanwhile rich countries will transfer significant funds and technologies to assist poorer countries to achieve their targets. Major CO2 emitters such as China and India argue that global reductions in CO2 emissions are the responsibility of rich countries because:
- countries such as China and India are still relatively poor and industrialisation, based on fossil fuels energy, is essential to raise living standards to levels comparable with those in the developed world
- historically, Europe and North America through their own industrialisation and economic development are largely to blame for contemporary global warming and climate change.
What is cap and trade?
Cap and trade offers an alternative, international market-based approach to limit CO, emissions. Under this scheme businesses are allocated an annual quota for their CO, emissions if they emit less than their quote they receive carbon credits which can be traded on intentional markets Businesses that exceed their quotes must purchase additional credits or incur financial penalties Carbon offsets are 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.
How can emissions be reduced from agriculture?
Land and crop management, livestock management, manure management.
What is land and crop management?
- Zero tillage- growing crops without ploughing the soil. This conserves the soils organic content, reducing oxidation and the risk of erosion by wind and water.
- Polyculture- growing annual crops interspersed with tress. Trees provide year round ground cover and protect soils from erosion.
- Crop residues- leaving crop residues (stems, leaves) on fields after the harvest to provide ground cover and protection against soil erosion and drying out.
- Avoiding the use of heavy farm machinery on wet soils, which leads to compaction and erosion by surface run off.
- Contour ploughing and terracing on slopes to reduce run-off and erosion.
- Introducing new strains of rice that grow in drier conditions and so produce lessCH4. Applying chemicals such as ammonium sulphate which inhibit microbial activities that produce CH4.
What is livestock management?
- Improving the quality of animal feed to reduce enteric fermentation so that less feed is converted to CH4: mixing methane inhibitors with livestock feed.
What is manure management?
- Controlling the way manure decomposes to reduce CH4 emissions. Storing manure in anaerobic containers and capturing CH4 as a source of renewable energy.
What are the management strategies to protect the global water cycle?
Forestry, water allocations, Drainage basins
