Maarg Manthan · Topic 15.10

Global Warming Potential (GWP)

Environment & Ecology › Climate Change Basics and Causes · Topic 15.10

Global Warming Potential (GWP) is an index that compares how much heat a given mass of a greenhouse gas traps over a chosen period, usually 100 years, relative to the same mass of carbon dioxide, which is defined as 1. It allows emissions of different gases to be added as carbon dioxide equivalent (CO2e), the common unit in inventories and climate treaties. GWP depends on how strongly a gas absorbs infrared radiation and how long it stays in the atmosphere. Using IPCC Sixth Assessment Report values for 100 years, methane has a GWP of about 27 to 30, nitrous oxide about 273, HFC-134a about 1,500, sulphur hexafluoride about 25,000 and nitrogen trifluoride about 17,000 to 18,000, while CFC-11 and CFC-12 are in the thousands; over 20 years methane is more than 80. Earlier reports used lower values, and the Kyoto Protocol uses values from the IPCC Second Assessment Report (methane 21, nitrous oxide 310). Related metrics include Global Temperature change Potential and the carbon dioxide equivalent of emissions over a time horizon. Lifetimes range from about 12 years for methane to over a thousand years for some fluorinated gases.

5 min read · UPSC Prelims · Environment & Ecology · Climate Change Basics and Causes

At a Glance

CO2 value 1
Methane About 27 to 30
Nitrous oxide About 273
SF6 About 25,000
Common horizon 100 years
Exam link UPSC Prelims, Environment & Ecology: Climate Change Basics and Causes

Where Does It Fit?

This is the last topic of the macro on climate change basics and causes. GWP turns the many gases discussed earlier into a single measure, and it leads into the next macro on climate impacts and mitigation. Previous topic: Ecological Footprint and Carbon Footprint. Next topic: Impacts of Climate Change: Acid Rain, El Niño, La Niña, Ozone Depletion, Ocean Acidification.

What Are the GWP Values of Key Gases?

Gas	100-year GWP (IPCC AR6, approximate) and lifetime
Carbon dioxide	1 by definition; persists for centuries to millennia
Methane	About 27 to 30; lifetime about 12 years; over 80 for a 20-year horizon
Nitrous oxide	About 273; lifetime about 109 years
HFC-134a	About 1,500; lifetime about 14 years
CFC-11 and CFC-12	Several thousand to over 10,000; long-lived
Sulphur hexafluoride	About 25,000; lifetime about 3,200 years
Nitrogen trifluoride	About 17,000 to 18,000; lifetime about 500 years

How Is GWP Used and What Are Its Limits?

CO2 equivalent: emission of a gas times its GWP gives CO2e
Inventories: national greenhouse gas reports use CO2e
Kyoto Protocol: uses GWPs from the IPCC Second Assessment Report: methane 21 and nitrous oxide 310
Time horizon: 20-year values emphasise short-lived gases, 100-year values are the standard
Limits: does not show timing or temperature; a gas with a short life looks smaller in a 100-year metric
Other metrics: Global Temperature change Potential and CO2-warming equivalents
Policy: HFC phase-down under the Kigali Amendment is based on GWP
Updates: values change with each IPCC report

What Else Should You Remember?

Definition: GWP is the integrated radiative forcing over a time horizon from a pulse emission of 1 kg of a gas, divided by that for 1 kg of CO2
CO2e: carbon dioxide equivalent, the standard unit in climate reports
Gigatonne: one billion tonnes
Factors: radiative efficiency, atmospheric lifetime and the time horizon
Methane in 20 years: over 80 times CO2 because of strong absorption and short life
Fossil methane: AR6 gives a slightly higher value for fossil methane than for biogenic methane
AR4 values: methane 25 and nitrous oxide 298
AR5 values: methane 28 and nitrous oxide 265
SAR values: methane 21 and nitrous oxide 310, used for Kyoto accounting
HFC-23: GWP of about 12,000 to 14,800, produced as a by-product of HCFC-22
CDM and HFC-23: early carbon credits were issued for destroying HFC-23
PFCs: perfluorocarbons such as CF4 have lifetimes of thousands of years
Water vapour: has no GWP because its amount is controlled by temperature
Ozone: short-lived, not assigned a normal GWP
Aerosols: have negative forcing, not covered in GWP
GTP: Global Temperature change Potential looks at temperature at a chosen year
GWP*: a newer metric to treat short-lived gases like methane better
India’s inventory: India’s Biennial Update Reports use GWP values from the IPCC reports
UNFCCC reporting: parties must use AR5 values for reporting under the Paris rules
Gas basket: Kyoto basket gases are all converted to CO2e
Link to previous: see Ecological Footprint and Carbon Footprint
Link to next: see Impacts of Climate Change: Acid Rain, El Nino, La Nina, Ozone Depletion, Ocean Acidification
Link to methane: see Methane Emission from Agricultural Practices
Caution: GWP numbers vary by IPCC report and gas, so always say which report and horizon
Exam hint: remember CO2 is 1, methane is about 25 to 30, N2O about 265 to 300, and SF6 is the highest
Hydrofluorocarbons: HFCs replaced CFCs in cooling but have GWPs in the hundreds to thousands, so the Kigali Amendment phases them down
Using GWP in practice: a tonne of methane counts as about 28 tonnes of CO2e, so cutting a small tonnage of methane gives large CO2e savings
Perfluorocarbons and aluminium: PFCs are released during aluminium smelting and chip manufacture
Why long-lived gases matter: gases that last thousands of years accumulate, so even small emissions add to future warming

Why Does It Matter for the Exam?

CO2: 1
Methane: About 28
Highest: SF6, about 25,000
Current affairs link: HFC phase-down
Common errors: ignoring the time horizon

As an analytical point, GWP makes it possible to compare gases, but the choice of time horizon affects the ranking. Methane looks modest over 100 years but is a prime target for quick climate gains over 20 years.

Why Is This Topic Important?

Base CO2 = 1
Depends Absorption, life
Unit CO2e

What Came Next?

The next macro covers the impacts of climate change and mitigation, beginning with acid rain, El Nino, La Nina, ozone depletion and ocean acidification. Next topic: Impacts of Climate Change: Acid Rain, El Niño, La Niña, Ozone Depletion, Ocean Acidification.

Key People and Terms

GWP Global Warming Potential
CO2e CO2 equivalent
GTP Global Temperature change Potential
Lifetime Time in air
Radiative efficiency Heat absorption strength
Time horizon Period for comparison

Exam Corner

Points to Remember

CO2 GWP is 1.
Methane about 28.
N2O about 265 to 273.
SF6 about 25,000.
Standard horizon: 100 years.

Do Not Confuse With

GWP and radiative forcing Gas comparison versus energy change
GWP and GTP Cumulative heat versus temperature at a date
GWP 20 and GWP 100 Short versus long horizon

Memory Hook

One for CO2, twenty-eight for methane, three hundred for laughing gas, SF6 on top.

Mains Angle

Questions ask for values and meaning. These points help.

Concept Comparison
Values Gas list
Limits Horizon

A Question You May Face

An original practice question, not a past paper question.

“What is Global Warming Potential? Explain how it is used to compare greenhouse gases and its limitations.”

How to Answer

Define GWP.
Values Methane, N2O.
Use CO2e.
Limits Horizon.

GS Relevance

Prelims: GWP values, CO2e, time horizon. GS Paper 3: climate metrics.

Frequently Asked Questions

What is Global Warming Potential?

Global Warming Potential measures how much heat a greenhouse gas traps over a set period, usually 100 years, compared with the same mass of carbon dioxide, which is set at 1. It depends on how strongly the gas absorbs heat and how long it stays in the air, and is used to convert emissions to CO2 equivalent.

What is the GWP of methane?

Using the IPCC Sixth Assessment Report, methane has a 100-year GWP of about 27 to 30, depending on whether it comes from fossil or biological sources, meaning a tonne of methane warms the climate about 27 to 30 times as much as a tonne of CO2 over a century. Over 20 years its GWP is more than 80.

Which greenhouse gas has the highest GWP?

Among common gases, sulphur hexafluoride has one of the highest GWPs at about 25,000 over 100 years, and nitrogen trifluoride is around 17,000. Some perfluorocarbons and CFCs are also very high. These gases are emitted in small quantities, but they last a very long time and trap a lot of heat.

What is carbon dioxide equivalent?

Carbon dioxide equivalent, or CO2e, is the amount of CO2 that would cause the same warming as a given amount of another greenhouse gas over a chosen time horizon. It is calculated by multiplying the gas emissions by their GWP, and allows countries to report all gases together in one figure.

Why does the time horizon matter for GWP?

Gases last different lengths of time. Methane lasts about 12 years, so its GWP is over 80 over 20 years but only 27 to 30 over 100 years, while long-lived gases such as CO2 and SF6 matter more over longer periods. The choice of horizon therefore affects how much priority a gas gets in policy.

PYQ Practice — Statement Analysis

1 The GWP of carbon dioxide is taken as 1.

True

By definition.

2 Methane has a lower GWP than CO2 over 100 years.

False

It is about 28 times higher.

3 SF6 has one of the highest GWPs.