Sun is the source of all energy and all life on earth. Sun emits energy in the form of short wave radiations (high energy i.e shortwave)-
- A part of which is reflected back by clouds, aerosols, atmosphere
- A part passes through the atmosphere to reach the earth’s surface which emits it back in the form of longwave radiation – Infra red (low energy, long wave) which warms the atmosphere <atmosphere is warmed by Longwave radiation not shortwave, hence temperature decreases with elevation so called lapse rate> <How does temperature inversion happen then?> and thus there is no net addition to earth’s temperature <oversimplified model but for now it would do>
Note here that, at night when earth would be the net emitter, temperature would reach dangerously low levels. Then how is avg temperature of earth is maintained at levels conducive to life on earth?
Role of Green Houses Gases
- Such gases present in the atmosphere serve as a blanket which trap/absorb some of that Infrared radiation emitted by earth and send some of that back to earth <this effect is k/as Greenhouse effect, you would have observed this in car parked in Sun> and thus help maintain average temperature of earth to 14 <w/o such gases avg temperature would be -16 and life would be impossible on earth>
- But any increase in such gases would result in more heat trapping resulting in increase in the temperature of earth being reflected in Global warming <Why is Venus hotter than Mercury when Mercury is closest to the Sun>
Global warming changes the climate of earth hence Global Warming and climate change are often used anonymously.
Most abundant GHGs in earth’s atmosphere are–
Water Vapour> CO2> CH4> N2O> Tropospheric Ozone>CFCs <plz note that tropospheric ozone is both a GHG and a pollutant, also included under Air Quality Index. Which other gases are included in AQI?>
- Water vapour has the max overall effect on greenhouse effect but as water vapour is not directly increased or decreased by Human activities, we are not concerned about amount of water vapour in the atmosphere <we are concerned about anthropogenic i.e human induced global warming>
- But as atmosphere warms, there would be more water vapour <more water getting converted into vapour> which would trap even more heat, resulting in even warmer atmosphere <positive reinforcement, so called vicious cycle so common in climate systems>
Global warming Effect of a GHG and GLobal Warming Potential (GWP)
Each gas’ effect on climate change depends on three main factors:
- How Much <higher the concentration, higher the warming>
- How long <more the life span, greater the warming>
- How Powerful <efficiency of heat trapping>
Last 2 factors together determine global warming potential
GWP over 100 years time scale <reference GWP of co2 (lifetime 30-95 years) being taken as 1>
- CH4 -25 <lifetime is only 12 years>
- N2O- 300 <lifetime of >100 years>
- CFC, HFCs, NF3, SF6 etc have over 1000 times GWP than that of CO2 as their lifetime is much longer <not easily degraded> and efficiency of trapping heat much higher.
Let’s Now look at Global Emission by Economic Source
Electricity and Heat Production (25%)>Agriculture, Forestry and land use changes (contribution of agriculture alone is 14%)>Industry (21%)
Kyoto Protocol of UNFCCC initially vowed to reduce concentration of 6 major GHGs and in 2nd Commitment period another gas was added. Let’s look at those 7 in detail
- CO2 – Burning down of Fossil fuels, cutting down and burning of Trees
Concentration of CO2 has increased from 280 in 1750 (pre industrial revolution) to 400 in 2015 i.e increased by 40%
- CH4- Primary source is Agriculture and Animal Husbandry <cows and sheep produce methane when they digest food>, manure when it decays, released from wetlands <waterlogged areas>, leakages during natural gas extraction, transportation < Natural gas is nothing but methane>
- N20– Excess use of nitrogenous fertilizers and bacteria breaking down nitrogen <what is nitrogen fixation and bacteria which helps in that?>, Fossil fuel Burning, Industrial process (nitric acid, synthetic fibres) <what is laughing gas and tear gas?>
- Hydrofluorocarbons (HFC)– refrigerants, aerosol propellants, solvents, and fire retardants. They were used as replacement to CFC and HCFC which was phased out under Montreal Protocol (deplete ozone layer) but they are even more powerful GHG. Now USA is trying to include HFC in montreal protocol even though they do not deplete ozone <what would then be used in refrigeration?>
- Perfluorocarbons (PFC) – aluminum production and semiconductors
- Sulfur Hexafluoride (SF6) – magnesium processing and semiconductor manufacturing, tracer gas for leak detection, electrical transmission equipment, induding circuit breakers.
- Nitrogen Trifluoride (NF3) – latest addition, uses similar to PFCs in electronics industry, semiconductors
- Note 1 – CFCs and HCFCs which are potent GHGs are not included in Kyoto Protocol as they were already being phased out under Montreal Protocol
- Note 2 – Only molecule containing both Chlorine and Fluorine deplete ozone layer, Fluorinated compounds do not, so HFC, NF3, SF6, PFC etc do not deplete ozone layer
Short Lived and Long Lived Climate Forcers
- Factors external to the climate system which force or push the climate towards a new long-term state – either warmer or cooler depending on the cause of change.
- For instance, GHGs would be positive climate forcers (both natural and anthropogenic) as they push climate warming.
- Long-life gases such as CO2, N2O,Fluorinated compounds once emitted exert their effect for long and are k/as Long Lived climate forcers.
- On the other hand gases such as Methane, tropospheric ozone have a very short life and reducing their emission will quickly lead to reduction in their concentration. Black Carbon or soot is one such very short lived climate forcer.
Black carbon –component of fine particulate matter and is formed through the incomplete combustion of fossil fuels and biomass. It’s a positive climate forcing agent and warms the atmosphere by –
- Directly absorbing sunlight
- Reducing albedo when deposited on snow and ice <what is albedo?>
- Indirectly by effects on cloud formation
It has major adverse health effects also <you know about PM 2.5> and contains many carcinogens <cancer causing agent>
Note- BC is the most effective form of PM, by mass, at absorbing solar energy: per unit of mass in the atmosphere, BC can absorb a million times more energy than CO2
- Effect of clouds on global warming?
- What is brown carbon and blue carbon?
Some short lived climate Forcers have cooling effects. For instance – Sulfur aerosols . Fossil fuel combustion emits sulfur dioxide also which then combines with water vapour to form tiny droplets (aerosols) which reflect sunlight <but aerosol lasts 3 days, CO2 warms for 100 years>. But same Sulfur/sulfate is responsible for acid rain
These aerosols are responsible for cooling observed after volcanic eruption and are being investigated for geoengineering <what is geoengineering?>
Now a few charts you need to look at carefully as they would form the basis of climate negotiations we would discuss in the next article
1. Top 10 Absolute emitters of the world
China is the world’s largest emitter and emits about 1/4th of total world emission. India is at 4th spot.
2. Top 10 Absolute emitter in per capita terms
Note that the chart below describes emissions of top 10 absolute emitters only. Among all countries, Qatar top the list. See how low India’s per capita emissions are
3. Emission intensity
It matters as India has pledged to reduce its emission intensity <by how much? what did China promise?> even though our intensity is already at the level of EU. One of the reason of our low intensity is domination of services sector which is comparatively less energy and GHG intense but as India tries to push it’s manufacturing sector achieving the target of emission intensity might become a tall order
4. Cumulative GHG emission
They describe a country’s total historic emissions and thus historical responsibility. Just look at the share of US and EU. India’s is not even 5% with 17% of global population
In the next part we will discuss climate negotiations.