CLIMATE CHANGE 

1. Global Warming

Earth has warmed at an unprecedented rate over the last hundred years & particularly over the last two decades. Since 1992, each year has been one of the warmest years on record.

2016 was the hottest year on record, worldwide. An upsurge in the number of extreme weather events, like wildfires, heat waves and strong tropical storms is also attributed.

Global warming is an average increase in the temperature of the atmosphere near the earth’s surface & in the troposphere, which can contribute to changes in global climate patterns.

Global warming can occur from a variety of causes, both natural & human-induced. In common usage, ‘global warming’ often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities.

Global warming Impacts:

• Changes in rainfall patterns
• Rise in sea level
• Melting of the icecaps
• Increased likelihood of extreme events like heat waves, flooding, hurricanes etc.
• Melting of glaciers
• Widespread vanishing of animal populations due to habitat loss
• Spread of disease
• Bleaching of coral reefs
• Loss of plankton due to warming of seas.

Greenhouse effect:

• The greenhouse effect is a naturally occurring phenomenon that blankets the earth's lower atmosphere & warms it, maintaining the temperature suitable for living organisms to survive.
•  Just as greenhouse gases, keep the air warm inside its chamber, water vapour & greenhouse gases warm the earth.
• Greenhouse gases play an important role in the balance of the earth’s cooling & warming.
• According to one estimate, in the absence of a naturally occurring greenhouse effect, the average temperature of the earth's surface would be -19⁰C instead of the present value of 15⁰C & the earth would be a frozen lifeless planet.
• A greenhouse/glasshouse is a building made of glass chambers in which plants are grown in cold countries or cold climate areas. There is a continued increase in temperature in green house even when the outside temperature remains low. It protects plants from frost.
• The greenhouse is a process caused by greenhouse gases, which occur naturally in the atmosphere. This process plays a crucial role in warming the earth’s surface, making it habitable.
• Human-generated greenhouse gas emissions upset the natural balance & lead to increased warmth.

Incoming Energy: The Sun emits energy which transmits to Earth. Because the sun is very hot, the energy is emitted in high-energy short wavelengths that penetrate the earth’s atmosphere.

Absorption: About 30% of the energy from the sun is reflected directly into space by the atmosphere, clouds, and surface of the earth. The rest of the sun’s energy is absorbed into the earth’s atmosphere.

Emission: The earth emits energy back into the atmosphere because the earth is cooler than the sun and the energy is emitted in the form of infrared radiation, at wavelengths longer than the incoming solar energy.

Role of Greenhouse gases:

Greenhouse gases in the atmosphere absorb much of the long-wave energy emitted from the earth’s surface, preventing it from escaping from the earth’s surface. The greenhouse gases then re-emit this energy in all directions, warming the earth’s surface & lower atmosphere.

Human role:

• The atmospheric concentration of greenhouse gases has increased significantly over the past two centuries, largely due to the human-generated carbon dioxide emissions from burning fossil fuels, and deforestation.
• This increase has amplified the natural greenhouse effect by trapping more of the energy emitted by the earth. This change causes the earth’s surface temperature to increase.

Greenhouse gases: Greenhouse gases are the gaseous constituents of the atmosphere, both natural & anthropogenic that absorb & re-emit infrared radiation.

Water Vapor

• Water vapour is the biggest overall contributor to the greenhouse effect & humans are not directly responsible for emitting this gas in quantities sufficient to change its concentration in the atmosphere.
• CO₂ & other gases are increasing the amount of water vapour in the air by boosting the rate of evaporation.
• Unlike CO₂, which can persist in the air for centuries, water vapour cycles through the atmosphere quickly, evaporating from the oceans and other sources before coming back, down as rain or snow.
• Since the rate of evaporation rises with temperature, the amount of water vapour in the air at any time is strongly related to the number of other greenhouse gases in the air.

Carbon dioxide(CO₂)

• CO₂ is the primary greenhouse gas emitted through human activities. Carbon dioxide is naturally present in the atmosphere as part of the earth’s carbon cycle.
• Human activities are altering the carbon cycle both by adding more CO₂ to the atmosphere & by reducing the natural sinks, like deforestation, to remove CO₂ from the atmosphere.
• While CO₂ emissions come from a variety of natural resources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the Industrial Revolution.

Sources

• The combustion of fossil fuels like gasoline & diesel used for transportation.
• The combustion of fossil fuels to generate electricity.
• Many industrial processes emit CO₂ through fossil fuel combustion.
• Several processes also produce CO₂ emissions through chemical reactions that do not involve combustion, for instance, the production & consumption of mineral products like cement, the production of metals like iron & steel, the production of chemicals etc.

 Trends & Emissions

• During 1990-2010, the increase in CO₂ emissions corresponded with increased energy use by an expanding economy & population.
• Changes in CO₂ emissions from fossil fuel combustion are influenced by many factors, including population growth, economic growth, changing energy prices, new technologies, changing behaviour, and seasonal temperatures.
• At present, the USA is the second largest greenhouse gas emitter.

Reducing CO₂ emissions: The most effective way to reduce carbon dioxide emissions is to reduce fossil fuel consumption. Other strategies include Energy Efficiency, energy conservation, Carbon Capture & sequestration.

Methane(CH₄): Methane is emitted by natural resources like wetlands, as well as human activities like leakage from natural gas systems & the raising of livestock. Natural processes in soil & chemical reactions in the atmosphere help remove methane from the atmosphere.

Sources: The wetlands are the largest natural sources, emitting methane from bacteria that decompose organic materials in the absence of oxygen. Smaller volcanoes include termites, oceans, sediments, volcanoes and wildfires. Anthropogenic sources include agriculture, industries, domestic & business wastes.

Nitrous oxide: Nitrous oxide(N₂O) is naturally present in the atmosphere as part of the earth’s nitrogen cycle and has a variety of natural sources. Human activities like agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of nitrous oxide in the atmosphere.

Sources:

• Natural emissions of N₂O are mainly from bacteria breaking down nitrogen in solids & oceans.
• Nitrous oxide is emitted when people add nitrogen to the soil through the use of synthetic fertilizers.
• Transportation- nitrous oxide is emitted when transportation fuels are burnt.
• Nitrous oxide is generated as a byproduct during the production of nitric acid, which is used to make synthetic commercial fertilizer and in the production of adipic acid, which is used to make fibres, like nylon and other synthetic products.
• Nitrous oxide is removed from the atmosphere when it is absorbed by certain types of bacteria/ destroyed by ultraviolet radiation or chemical reactions.

Fluorinated gases:

• Fluorinated gases are eliminated through a variety of industrial processes like aluminium, semiconductor manufacturing & substitution for ozone-depleting substances.
• Many fluorinated gases have very high global warming potentials(GWPs) relative to other greenhouse gases.
• Fluorinated gases are well-mixed in the atmosphere, spreading around the world after they are united.
• They are removed from the atmosphere only when they are destroyed by sunlight in the far atmosphere.
• In general, fluorinated gases are the most potent & longest lasting type of greenhouse gas emitted by human activities.
• There are three main categories of fluorinated gases:

1. Sulfur hexafluoride(SF₆)
2. Hydrofluorocarbons(HFCs)
3. Perfluorocarbons(PFCs)

Substitution for ozone-depleting substances: HFCs are used in refrigerators, aerosol propellants, solvents and fire retardants. These chemicals were developed as a replacement for chlorofluorocarbons(CFCs) and HFCs because they do not deplete the stratospheric ozone layer. HFCs are potent greenhouse gases with long atmospheric lifetimes and they are released into the atmosphere through leaks, servicing & disposal of equipment in which they are used.

Industry:

• PFCs are compounds produced as a byproduct of various industrial processes associated with aluminium production & the manufacturing of semiconductors.
• Like HFCs, PFCs generally have long atmospheric lifetimes.
• SF₆ is used in magnesium processing & semiconductor manufacturing, as well as tracer gas for leak detection.
• HFC-23 is produced as a by-product of HFC-22 production.

Transmission & distribution of electricity: Sulfur hexafluoride is used in electrical transmission equipment, including circuit breakers.

Black carbon: Black carbon(BC) is a solid particle or aerosol, contributing to the warming of the atmosphere. Black carbon, commonly known as soot is a form of particulate air pollutant, produced from incomplete combustion. It consists of pure carbon in several linked forms.

Sources: Biomass burning, Diesel exhaust and Cooking with solid fuels etc.

Effects: Black carbon is the strongest absorber of sunlight & heats the air directly. In addition, it darkens snow packs & high glaciers through deposition & leads to the melting of ice and snow. BC warms the earth by absorbing heat in the atmosphere & by reducing albedo when deposited on snow & ice. Regionally, BC disrupts cloudiness & monsoon rainfall & accelerates the melting of mountain glaciers like the Hindu Kush-Himalayan glaciers.

Lifetime: BC stays in the atmosphere for only several days to weeks. Thus the effects of BC on atmospheric warming & glacier retreat disappear within months of reducing emissions.

India’s contribution: According to estimates, between 25 & 35% of BC in the global atmosphere comes from China, and India emitted from the burning of wood & cow dung in household cooking & through the use of coal to heat homes.

Project Surya has been launched to reduce black carbon in the atmosphere by introducing efficient stove technologies, solar cookers, solar lamps and biogas plants.

Brown carbon:

• Brown carbon is a ubiquitous & unidentified component of organic aerosol which has recently come to the forefront of atmospheric research.
• Light absorbing organic matter in atmospheric aerosols of various origins like soil humus, humus-like substances, tarry materials from combustion, bioaerosols etc.
• Biomass burning is shown to be a major source of brown carbon.
• Smoke from agricultural fires may be an additional source.
• Brown carbon is generally referred to as greenhouse gases and black carbon for particles resulting from impure combustion like soot & dust.

2. Climate Forcings

• Climate forcings are factors in the climate system that either increase or decrease the effects on the climate system.
• Positive forcings like excess greenhouse gases warm the earth while negative forcings like the effects of most aerosols & volcanic eruptions cool the earth.
• Atmospheric aerosols include volcanic dust, soot from the combustion of fossil fuels, particles from burning forests & mineral dust.
• Dark carbon-rich particles like soot from diesel engines absorb sunlight & warm the atmosphere.
• Conversely, exhaust from high-sulfur coal or oil produces light aerosols that reflect sunlight to space, producing a cooling effect.
• Aerosols that form naturally during volcanic eruptions cool the atmosphere.
• Large volcanic eruptions can eject enough ash into the atmosphere to lower temperature for a year or more until the sulfate particles settle out of the atmosphere.

Altering the energy balance:

• The power of the process to alter the climate is estimated by its radioactive forcing, the change in the earth’s energy balance due to that process.
• Some climate forcings are positive, causing globally averaged warming and some are negative, causing cooling.
• Some, like an increased form of carbon dioxide concentration are well known; others such as from aerosols are more uncertain.

Natural forcings: Natural forcings include changes in the amount of energy emitted by the sun, very slow variations in the earth’s orbit and volcanic eruptions. Since the start of the Industrial Revolution, the only natural force with any long-term significance has been a small increase in solar energy reaching Earth.

Anthropogenic forcings:

• Climate forcings can also be caused by human activities. These activities include greenhouse gases & aerosol emissions from burning fossil fuels & modifications of the land surface like deforestation.
• Greenhouse gases are positive climate forcing. They have a warming effect.
• Carbon dioxide emitted from the burning of fossil fuel is presently the largest single climate-forcing agent, accounting for more than half of the total positive forcing since 1750.
• Burning fossil fuels adds aerosols to the atmosphere. Aerosols are tiny particles in the atmosphere composed of many particles like water, ice, ash, mineral dust, and acidic droplets.

Estimating the effect of gases:

Each gas’s effect on climate change depends on 3 main factors:

• Concentration or abundance, is the amount of a particular gas in the air. Greenhouse gas concentrations are measured in parts per million, parts per billion & even parts per trillion.
• One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid .
• Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years.
• All of these gases remain in the atmosphere long enough to become well mixed, meaning that the amount measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.
• Some gases are more effective than others at making the planet warmer & thickening the Earth’s blanket.
• For each greenhouse gas, a global warming Potential(GWP) has been calculated to reflect how long it remains in the atmosphere on average and show how strongly it absorbs energy.

Global warming Potential:

• Global warming potential describes the impact of each gas on global warming.
• The two most important features of a GHG in terms of climate impact are how well the gas absorbs energy and how long the gas stays in the atmosphere.
• GWP for a gas is a measure of the total energy that a gas absorbs over a particular period, compared to carbon dioxide.
• Gases with a higher GWP absorb more energy, per pound than gases with a lower GWP and thus contribute more to warming earth.

Carbon dioxide has a GWP of 1 & serves as a baseline for other GWP values.

• The larger the GWP, the more warming the gas causes. For instance, methane’s 100-year GWP is 21, which means that methane will cause 21 times as much warming as an equivalent mass of carbon dioxide over 100 years.
• Methane has a GWP more than 20 times higher than CO₂ for a 100-year time scale. Methane emitted today lasts for only 12 years in the atmosphere, on average. However, on a pound-for-pound basis, methane absorbs more energy than carbon dioxide, making its GWP higher.
• Nitrous oxide has a GWP 310 times that of CO₂ for a 100-year time scale. N₂O emitted today remains in the atmosphere for an average of 120 years.
• Chlorofluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, perfluorocarbons, and sulfur hexafluoride are called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO₂.

Receding Glaciers:

150 years ago there were 147 glaciers in Glacier National Park, but today only 37 glaciers remain and scientists predict that they are likely to melt by the year 2030. Similarly, glaciers all across the Himalayas & Alps are retreating & disappearing every year.

There are almost 160,000 glaciers found in Polar Regions & high mountain environments. Therefore, researchers are increasingly using satellite remote sensors to routinely survey our world’s glaciers in a fraction of the time.

Impact of Glacial Retreat:

• The retreat of glaciers in the Andes & the Himalayas will have a potential impact on water supplies.
• Climate change may cause variations in both temperature & snowfall, causing changes in the mass balance of a glacier.
• The Himalayas & other mountain chains of central Asia support large regions that are glaciated.
• These glaciers provide critical water supplies to dry countries like Mongolia, western China, Pakistan and Afghanistan.
• The loss of these glaciers would have a tremendous impact on the ecosystem of the region.
• World’s leading scientists predict that global warming may pose a serious threat to the national & global economy & the environment.
• The poor & low-lying countries will find it difficult to cope with the damages caused by changing climate & rise in sea level.

Chain of Events: Combustion of fossil fuels due to Human Activities-àincrease in greenhouse gases-àglobal warming-àclimate changes-àmelting of glaciers-àflooding/rise in sea level-àsubmergence of low-lying coastal lands-àlarge-scale destruction of ecosystems & extinction of species.