What is Global Warming Potential?

What is Global Warming Potential?

Global warming potential (GWP) is a metric that compares the warming effect of a given mass of greenhouse gas to the same mass of carbon dioxide (CO₂) over a specified time period, typically 100 years (GWP-100). CO₂ serves as the reference gas with a GWP of 1. Methane (CH₄) has a GWP-100 of approximately 28–30, meaning one ton of methane traps 28–30 times more heat than one ton of CO₂ over a century. Nitrous oxide (N₂O) has a GWP-100 of roughly 265. GWP values enable conversion of all greenhouse gases into a common unit—CO₂ equivalents (CO₂e)—for reporting, regulation, and trading.

Why It Matters

GWP underpins virtually every greenhouse gas inventory, carbon footprint calculation, and emissions regulation worldwide. The Kyoto Protocol, the Paris Agreement, national emissions inventories, corporate GHG disclosures, and carbon market transactions all rely on GWP values to aggregate different gases into comparable CO₂e figures. When a company reports its Scope 1, 2, and 3 emissions, it uses GWP values from the IPCC Assessment Reports to convert methane, nitrous oxide, fluorinated gases, and other non-CO₂ emissions into CO₂ equivalents.

The choice of time horizon matters enormously and is increasingly contested. Methane's GWP-20 (20-year horizon) is approximately 80–84—nearly three times its GWP-100 of 28–30—because methane is a potent but short-lived gas that degrades in the atmosphere within about 12 years. The conventional use of GWP-100 therefore significantly understates methane's near-term warming impact. This has real policy implications: the Global Methane Pledge, signed by over 150 countries, targets a 30% methane reduction by 2030 precisely because cutting short-lived climate pollutants delivers rapid climate benefits that GWP-100 underrepresents.

For corporations, GWP selection directly affects reported emissions magnitude and strategic priorities. A dairy company's methane emissions look very different through a GWP-20 lens versus GWP-100. The oil and gas sector's fugitive methane emissions become far more material at GWP-20 values. Some reporting frameworks and investors now request GWP-20 supplementary reporting alongside the standard GWP-100, particularly for methane-intensive sectors.

Fluorinated gases illustrate extreme GWP scenarios. Sulfur hexafluoride (SF₆), used in electrical switchgear, has a GWP of 23,500—meaning one kilogram has the warming impact of 23.5 tons of CO₂. HFCs used in refrigeration and air conditioning have GWPs ranging from 12 to 14,800. The Kigali Amendment to the Montreal Protocol phases down HFC production specifically because of their extraordinary GWPs, driving the transition to lower-GWP alternatives.

How It Works / Key Components

GWP is calculated by integrating the radiative forcing (additional heat trapped per unit concentration) of a pulse emission of a gas over a specified time horizon, compared to the same calculation for CO₂. Three gas properties determine GWP: absorption efficiency (how strongly the gas absorbs infrared radiation per molecule), atmospheric lifetime (how long the gas persists before breaking down), and the spectral overlap with other gases (whether it absorbs at wavelengths already absorbed by more abundant gases).

The IPCC periodically updates GWP values as scientific understanding of atmospheric chemistry improves. The GHG Protocol requires companies to use IPCC Fifth Assessment Report (AR5) values, while national inventories under the UNFCCC currently use AR5 or are transitioning from AR4. AR6, published in 2021, slightly revised several GWP values—methane's GWP-100 increased from 28 (AR5) to 29.8 (AR6) due to updated understanding of methane's indirect effects on atmospheric chemistry.

CO₂ equivalent (CO₂e) is the practical output of GWP conversions. Multiplying the mass of each greenhouse gas by its GWP yields CO₂e, enabling apples-to-apples comparison. A facility emitting 100 tons of CO₂, 5 tons of CH₄, and 0.5 tons of N₂O has CO₂e emissions of approximately 100 + (5 × 28) + (0.5 × 265) = 372.5 tons CO₂e using AR5 GWP-100 values.

Alternative metrics exist. GWP* attempts to better represent the temperature impact of short-lived gases by distinguishing between changes in emission rates versus sustained emissions. GTP (Global Temperature Potential) measures the temperature change at a specific future point rather than cumulative forcing. These alternatives haven't displaced GWP in policy and reporting frameworks but inform scientific debate about optimal climate metrics.

Council Fire's Approach

Council Fire ensures clients apply correct and current GWP values in greenhouse gas inventories and understand how metric choices affect their emissions profile and strategic priorities. We help organizations navigate the transition between IPCC assessment report values, evaluate GWP-20 supplementary reporting for methane-intensive sectors, and translate GWP-based emissions data into actionable reduction strategies aligned with science-based targets.

Frequently Asked Questions

Which IPCC GWP values should my company use for reporting?

The GHG Protocol Corporate Standard specifies AR5 GWP-100 values as the current requirement. CDP and most voluntary frameworks follow GHG Protocol guidance. National regulatory programs may specify different assessment report values—check your jurisdiction. If you operate in methane-intensive sectors, consider supplementary GWP-20 reporting to demonstrate awareness of near-term warming impact, as investor and regulatory interest in methane-specific metrics is growing rapidly. Always document which GWP values and assessment report you're using for transparency and comparability.

Why is there controversy over GWP-100 versus GWP-20?

GWP-100 favors long-lived gases by spreading their cumulative impact over a century where they persist, while diluting the intense near-term impact of short-lived gases like methane. Critics argue this masks the urgency of methane reduction, which delivers the fastest available temperature response. Proponents of GWP-100 argue it captures the cumulative climate impact more comprehensively and that switching metrics mid-stream would disrupt established reporting, trading, and regulatory systems. The practical compromise emerging in policy is to report GWP-100 as the primary metric while providing GWP-20 supplementary data for short-lived pollutants.

How do GWP values affect carbon credit and offset markets?

GWP values directly determine the CO₂e credit volume generated by projects that reduce non-CO₂ gases. A project capturing methane from a landfill receives 28 CO₂e credits per ton of methane destroyed (at GWP-100). If markets shifted to GWP-20, the same project would generate 80+ credits per ton. This creates significant financial sensitivity to GWP methodology. Carbon market standards (Verra VCS, Gold Standard) specify which GWP values to use, and any updates to required values directly affect project economics and credit supply.