What are Greenhouse Gases ?

The word greenhouse is associated to the property of the gas to absorb infrared radiation.

As per the basic law of thermodynamics the wavelength of radiation emitted by the body depends upon the temp of the body and hence most of the INSOLATION ( incoming solar radiation) from the sun passes through the earth’s atmosphere and most of this radiation received from the sun is in visible spectrum (Ozone absorbs most of the radiation in the UV spectrum). As the energy is received from the sun the earth starts to heat up and other process driven by the energy of the sun happen on the earth . The earth in order to maintain its temperature also has to give out the excess energy ( otherwise the earth in its long and continuous exposure to the sun would simply melt away!!!!!)

The earth being at much lower temperature from the sun emits this radiation mainly in the infrared spectrum.

And it this IR radiation which some gases absorb in the atmosphere and result in the so called greenhouse effect. Hence these gases are called greenhouse gasses.

Each gas's effect on climate change depends on three main factors:

How much of these gases are in the atmosphere?

Concentration, or abundance, is the amount of a particular gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion. One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid (roughly the fuel tank of a compact car).

How long do they stay in the atmosphere?

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 that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.

How strongly do they impact global temperatures?

Some gases are more effective than others at making the planet warmer and "thickening the Earth's blanket."

For each greenhouse gases, a Global Warming Potential (GWP) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs

energy. 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 (CO 2) : Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or "sequestered") when it is absorbed by plants as part of the biological carbon cycle.

Properties of Carbon Dioxide

Chemical Formula CO2

Lifetime in Atmosphere

50-200 years

Global Warming Potential (100-year)

1

Carbon dioxide (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 (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). Human activities are altering the carbon cycle--both by adding more CO2 to the atmosphere and by influencing the ability of natural sinks, like forests, to remove CO2 from the atmosphere. While CO2 emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution. 

Methane (CH 4)   : Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

Properties of Methane

Chemical Formula CH4

Lifetime in Atmosphere

12 years

Global Warming Potential (100-year)

21

Methane is more abundant in Earth’s atmosphere now than at any time in at least the past 650,000 years. [2] Due to human activities, CH4concentrations increased sharply during most of the 20th century and are now more than two-and-a-half times pre-industrial levels. In recent decades, the rate of increase has slowed considerably. [

Nitrous oxide (N 2O)   : Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.

Properties of Nitrous Oxide

Chemical Formula N2O

Lifetime in Atmosphere

120 years

Global Warming Potential (100-year)

310

Concentrations of N2O have risen approximately 18% since the start of the Industrial Revolution, with a relatively rapid increase towards the end of the 20th century. 

Fluorinated gases   : Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases ("High GWP gases").

Properties of F-gases

Chemical Formula

HFCs, PFCs, SF6

Lifetime in Atmosphere

HFCs: 1-270 yearsPFCs: 800-50,000 yearsSF6: 3,200 years

Global Warming Potential (100-year)

HFCs: 140-11,700PFCs: 6,500-9,200SF6: 23,900

Unlike many other greenhouse gases, fluorinated gases have no natural sources and only come from human-related activities. Like other long-lived greenhouse gases, fluorinated

gases are well-mixed in the atmosphere, spreading around the world after they're emitted. Fluorinated gases are removed from the atmosphere only when they are destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by human activities.

According to the Second IMO GHG ( Green house Gas )Study 2009, which is the most comprehensive and authoritative assessment of the level of GHG emitted by ships, international shipping was estimated to have emitted 870 million tonnes, or about 2.7% of the global man-made emissions of CO2 in 2007. Exhaust gases are the primary source of GHG emissions from ships and carbon dioxide is the most important GHG, both in terms of quantity and of global warming potential.

The Study identifies a significant potential for reduction of GHG emissions through technical and operational measures. The Study estimates that, if implemented, these measures could increase efficiency and reduce the emissions rate by 25% to 75% below the current level. IMO’s Marine Environment Protection Committee (MEPC) has given extensive consideration to control of GHG emissions from ships and finalized in July 2009 a package of specific technical and operational reduction measures.  In March 2010 MEPC started the consideration of making the technical and operational measures mandatory for all ships irrespective of flag and ownership.  This work was completed in July 2011 with the breakthrough adoption of technical measures for new ships and operational reduction measures for all ships, which are, consequently, the first ever mandatory global GHG reduction regime for an entire industry sector.  The adopted measures add to MARPOL Annex VI a newChapter 4 entitled “Regulations on energy efficiency for ships”, making mandatory the Energy Efficiency Design Index (EEDI) for new ships and the Ship Energy Efficiency Plan (SEEMP) for all ships.  The regulations apply to all ships over 400 gross tonnage and above and are expected to enter into force through the tacit acceptance procedure on 1 January 2013.  

Energy Efficiency Design Index

The EEDI for new ships is the most important technical measure and it aims at promoting the use of more energy efficient (less polluting) equipment and engines.  The EEDI requires a minimum energy efficiency level per capacity mile (e.g. tonne mile) for different ship type and size segments.  From 1 January 2013, following an initial two year phase zero when new ship design will need to meet the reference level for their ship type, the level is to be tightened incrementally every five years, and so the EEDI is expected to stimulate continued innovation and technical development of all the components influencing the fuel efficiency of a ship from its design phase.  The EEDI is a non-prescriptive, performance-based mechanism that leaves the choice of technologies to use in a specific ship design to the industry.  As long as the required energy efficiency level is attained, ship designers and builders are free to use the most cost-efficient solutions for the ship to comply with the regulations.  The EEDI provides a specific figure for an

individual ship design, expressed in grams of carbon dioxide (CO2) per ship’s capacity-mile (the smaller the EEDI the more energy efficient ship design) and is calculated by a formula based on the technical design parameters for a given ship. The CO2 reduction level (grams of CO2 per tonne mile) for the first phase is set to 10% and will be tightened every five years to keep pace with technological developments of new efficiency and reduction measures.  Reduction rates have been established until the period 2025 to 2030 when a 30% reduction is mandated for applicable ship types calculated from a reference line representing the average efficiency for ships built between 2000 and 2010.  The EEDI is developed for the largest and most energy intensive segments of the world merchant fleet and will embrace 72% of emissions from new ships covering the following ship types: oil tankers, bulk carriers, gas carriers, general cargo, container ships, refrigerated cargo and combination carriers.  For ship types not covered by the current formula, suitable formulas are expected to be developed in the future addressing the largest emitters first. 

Ship Energy Efficiency Management Plan and Energy Efficiency Operational Indicator

The Ship Energy Efficiency Management Plan (SEEMP) is an operational measure that establishes a mechanism to improve the energy efficiency of a ship in a cost-effective manner.  The SEEMP also provides an approach for shipping companies to manage ship and fleet efficiency performance over time using, for example, the Energy Efficiency Operational Indicator (EEOI) as a monitoring tool.  The guidance on the development of the SEEMP for new and existing ships incorporates best practices for fuel efficient ship operation, as well as guidelines for voluntary use of the EEOI for new and existing ships (MEPC.1/Circ.684).  The EEOI enables operators to measure the fuel efficiency of a ship in operation and to gauge the effect of any changes in operation, e.g. improved voyage planning or more frequent propeller cleaning, or introduction of technical measures such as waste heat recovery systems or a new propeller.  The SEEMP urges the ship owner and operator at each stage of the plan to consider new technologies and practices when seeking to optimise the performance of a ship.

 

2012 Guidelines on Technical and Operational Measures

Further to the adoption of a global energy standard at MEPC 62 (July 2011), MEPC 63 (March 2012) adopted four sets of important guidelines to assist in the implementation of the mandatory regulations on Energy Efficiency for Ships in MARPOL Annex VI:

1. 2012 Guidelines on the method of calculation of the attained Energy Efficiency Design Index (EEDI) for new ships, resolution MEPC.212(63);

2. 2012 Guidelines for the development of a Ship Energy Efficiency Management Plan (SEEMP), resolution MEPC.213(63);

3. 2012 Guidelines on survey and certification of the Energy Efficiency Design Index (EEDI), resolution MEPC.214(63); and

4. Guidelines for calculation of reference lines for use with the Energy Efficiency Design Index (EEDI), resolution MEPC.215(63).

Finalization and adoption of the supporting guidelines was a significant achievement which provides sufficient lead time for Administrations and industry to prepare.  The guidelines will support Member States in their uniform implementation of the new chapter 4 of MARPOL Annex VI Regulations for the prevention of air pollution from ships.