CHAPTER 21: THE ENHANCED GREENHOUSE EFFECT (Chlorofluorocarbons &…
CHAPTER 21: THE ENHANCED GREENHOUSE EFFECT
The contribution a gas makes to the greenhouse effect depends upon:
The capacity of the gas to absorb heat (its global warming potential in comparison to CO2, which is given a rating of one)
The length of time it persists in the atmosphere.
Its concentration in the atmosphere.
After water vapour, the three most prevalent greenhouse gases in the Earth's atmosphere are CO2, methane and nitrous oxide, respectively.
The atmospheric abundances of these gases are directly connected with human activity.
The abundance of water vapour (the most important greenhouse gas) is controlled by fast climate feedback mechanisms.
Carbon Dioxide :warning:
Carbon Sequestration in Natural Systems
Carbon sequestration or storage is a natural part of the carbon cycle and has been happening for billions of years on Earth. in natural systems carbon Cycles continuously from organisms to the atmosphere: CO2 is released by the respiration of organisms and decomposition of organic material and is take it up by plants in photosynthesis.
CO2 is removed from the cycle into long-term storage in all of Earth's major systems: The atmosphere, hydrosphere, lithosphere and biosphere
The ocean is a major carbon sink
Up to 40% of the Earth's carbon emissions are absorbed and stored in the oceans because carbon dioxide dissolves in sea water to form carbonic acid.
Call Ocean Waters are more effective at sinks and warm Waters
Plants and animals store carbon
Phytoplankton is the basis of the marine food chain; these tiny plants take up CO2 which become Incorporated into the biomass of the oceans. CO2 is also incorporated into the shelves of many aquatic organisms as calcium carbonate. as these organisms dial therefore to the ocean floor and over a long period they are contacted into limestone to the carbon is locked up for thousands of years or water may dissolve the limestone and so make the carbon available again.
the increasing concentration of carbonic acid is making the oceans more acidic.
It is a threat for many marine organisms that have calcium carbonate shells all skeletons including Corals mussels and some plankton.
Forests are the most widely cited carbon sinks.
tropical and old growth forests have the highest carbon storage potential. install Forest carbon maybe store four centuries while another Forest carbon is released because of the fire or deforestation or simply because the trees are not as long lived
NOTE: not all of the stored CO2 is released when a forest is destroyed. The carbon that remains as plant tissue is consumed by animals or added to the soil as litter when plants decompose.
The primary way that carbon is stored in the soil is as soil organic matter. Carbon can remain stored in soils for millennia, or it can be quickly released back into the atmosphere.
About 30% of a tree’s biomass is in its roots, and this figure is likely to be higher for trees growing on less fertile soils where they need more extensive root systems. After forest clearing, the rate of release of carbon dioxide from the soil depends on how rapidly the soil microflora decompose the roots.
The rate of carbon release from the soil is high if the land is cleared for grazing, while on improved pastured (where crops are sown), the carbon levels do not drop much.
Climactic conditions, natural vegetation, soil texture and drainage all affect the amount and length of time carbon is stored.
Carbon dioxide measured in parts per million(ppm) by volume is the major contributor to the enhanced greenhouse effect. the concentration of CO2 in the atmosphere has increased from 280 ppm before the Industrial Revolution 400 ppm in 2014, the highest recorded in history
This represents an increase of about 43%, and levels have been predicted to increase further over the next 50 years. the current CO2 increase is about 0.5% per year.
most of This is increase is the result of burning fossil fuels, clearing and burning forests.
The yearly output of CO2 is estimated at over 19000 million tonnes. about half of this is taken up by the atmosphere and the rest is absorbed by vegetation all dissolved in the oceans
The third most prevalent greenhouse gas in the Earth’s atmosphere.
Produced naturally by the breakdown of organic material in environments, where the supply of oxygen is limited and CO2 cannot form.
Human activities, including extracting fossil fuels, leaving vegetation to rot in rice paddies, burning biomass, disposing of garbage in landfills, treating sewage and farming ruminant animals (such as cows) - account for some 60% of atmospheric methane emissions.
Natural processes, including the release of methane from wetlands (produced by decaying peat in bogs and tundra) and termite activity - account for the remaining 40%.
It is in a relatively low concentration in the atmosphere but has a global warming potential 21 times that of CO2 due to its molecular spectral characteristics. I.e 1 molecule of methane has 21 times the ability of 1 molecule of CO2 to absorb reradiated heat.
Concentrations of methane have remained relatively stable over the past few years, although current levels are about 154% higher than the pre-industrial concentration of 700 ppb.
Occurs naturally in the atmosphere at very low concentrations
Conc increase due to: chemical manufacture, fertiliser use, soil cultivation, catalytic converters in cars and growing leguminous crops.
Human activity accounts for 40% of all N2O emissions.
It has a significant contribution to the greenhouse gas effect because it has 310 times the capacity of CO2 to absorb heat.
Chlorofluorocarbons & Halons
Do not occur naturally in the atmosphere.
They have a greenhouse effect more than 5000 times that of CO2. Once produced they resist chemical breakdown in the atmosphere and may persist over 100 years.
Example: used in fridges and air conditioning, as propellants in aerosol spray cans, manufacture of foam products for packaging and insulation. Halons used in some fire extinguishers.
CFCs and Halons are being phased out in accordance with international treaties
Major contributors to the depletion of the ozone layer.
Replacements include hydrofluorocarbons (HFCs) - are less harmful to the ozone layer but are still powerful greenhouse gases.
It is a greenhouse gas in the troposphere. It is the major product of the action of ultraviolet radiation on atmospheric hydrocarbons and nitrogen oxides produced from car exhausts and coal-burning plants, resulting in photochemical smog...
As it is close to the ground, it irritates the respiratory systems of animals and damages trees.
The greenhouse contribution of troposphere ozone is very low (about 0.03ppm), however there have been increases in recent years in the northern hemisphere mainly.
Tropospheric ozone conc are increasing at an annual rate of 0.5% and there will be greater increase, reflecting the level of fossil fuel combustion.
Australia's Contribution to the Enhanced Greenhouse Effect
Australia accounts for only about 1.5% of global emissions. (but still the top 20 emitters in the world).
The pattern of greenhouse gas emissions in Australia since 1990 has been recorded in the National Greenhouse Gas Inventory.
The largest increase in greenhouse gas emissions from 1990 to 2015 (of about 42%) occurred in the stationary energy sector.
Driven by an increasing population, increasing household incomes and increasing resources exports. Transport is the next largest growth sector (increase of 30%) due to increases in the no. of vehicles per household.
Aus's high per capita emissions due to:
reliance on brown coal for electricity production
Emission-intensive extraction and processing of mining resources, which are largely destined for export
large-scale primary production - agriculture is emission-intensive and the products are consumed overseas.
High levels of vehicle use owing to our sparse population and poor public transport options outside major hubs.
Enhanced Greenhouse Effect :warning:
When a higher concentration of greenhouse gases leads to more heat energy being absorbed in the atmosphere and a gradual warming of the Earth's surface temperature.
Main reasons for increases:
The increased combustion of fossil fuels and associated release of greenhouse gases in response to the growth in energy demand in both developed and developing countries.
The loss of vegetation cover (and therefore of forests acting as carbon sinks) due to the expansion of agriculture activities resulting from population pressures.
The manufacture and use of artificial gases such as chlorofluorocarbons (CGCs) and Hydrochlorofluorocarbons (HCFCs)
Major factors that alter Earth’s atmosphere
• the structure of the atmosphere and the relative proportions of different gases, including greenhouse gases, that regulate the natural and enhanced greenhouse effects
• the lifespans of greenhouse gases and their ability to absorb infra-red radiation and hence their warming potentials????
• carbon sequestration in land, water and air that results in short-term (<100 years) and long-term (>1000 years)
• the altered proportions of different gases in the atmosphere over time resulting from human activities including use of fossil fuels.???
Water Vapour :warning:
A greenhouse gas - so it will contribute to global warming
Generally not considered in greenhouse gas inventories as there is little direct human contribution to the conc of this gas in the atmosphere.
However as the Earth's temp rises, the atmosphere will hold more water vapour - which may increase cloud cover and thus reduce surface temperatures as the clouds reflect more heat and light back into out space.
have a direct influence on the greenhouse effect by scattering and reflecting short-wave radiation. This reflection of incoming solar radiation can have a cooling effect.
Aerosols also affect the formation of clouds. The aerosol particles become the nuclei for the condensation of water droplets and the formation of clouds.
Clouds formed in polluted air are brighter due to the pollutants causing early nucleation of water vapour into water. THese clouds reflect more solar radiation, leading to further cooling of the Earth's surface.
A group of artificial gases that absorb infrared radiation.
The molecules of these gases are extremely stable and can persist in the atmosphere for thousands of years.
Largely produced during the electrolytic production of aluminium (also in electronics, fridges, medical and cosmetic purposes)
Emissions have decreased due to improved methods of aluminium processing.