Global Warming Potential (GWP)

What is Global Warming Potential?

Global Warming Potential (GWP) is a relative measure of how much heat a greenhouse gas traps in the atmosphere compared to CO₂ over a specified time period (usually 100 years, GWP100). CO₂ has a GWP of 1 by definition, and all other gases are measured relative to it.

GWP depends on the gas's radiative efficiency (how much heat it absorbs per molecule) and atmospheric lifetime (how long it persists). Methane (CH₄) has a high radiative efficiency but short lifetime (~12 years), giving it a GWP100 of 28. Some fluorinated gases persist for thousands of years with GWPs exceeding 20,000.

GWP values are published by the IPCC and updated in each Assessment Report. The AR6 (2021) values are used in current reporting frameworks. GWP allows comparison of different gases on a common CO₂-equivalent basis, essential for regulatory compliance and emissions trading.

Formula: CO₂e (kg) = Gas Quantity (kg) × GWP Factor Key GWP100 values (AR6): CO₂ = 1, CH₄ = 27.9, N₂O = 273, HFC-134a = 1,530, SF₆ = 25,200

Example Calculation

A facility emits 100 tonnes CO₂, 2 tonnes CH₄, and 0.5 tonnes N₂O annually. CO₂e = 100×1 + 2×27.9 + 0.5×273 = 100 + 55.8 + 136.5 = 292.3 tonnes CO₂e. Despite being the smallest by mass, N₂O contributes the most warming impact.

When to Use This Calculator

• Converting non-CO₂ greenhouse gas emissions (methane, nitrous oxide, fluorinated gases) to CO₂-equivalent for aggregated reporting
• Assessing the relative warming impact of different emission sources — a small mass of high-GWP gas may contribute more warming than a large mass of CO₂
• Evaluating refrigerant transition options by comparing the GWP of current refrigerants (R-410A, R-404A) against low-GWP alternatives (R-32, R-1234yf)
• Preparing GHG inventories that require all gases to be reported on a common CO₂e basis for regulatory or voluntary disclosure

Common Mistakes to Avoid

• Using GWP20 values when the reporting framework requires GWP100 — this would overstate methane's impact by 3× and create non-comparable results
• Applying GWP to CO₂ biogenic emissions without disclosure — biogenic CO₂ (from biomass combustion) is reported separately under the GHG Protocol and should not simply be multiplied by GWP = 1 and added to fossil CO₂
• Forgetting that GWP values differ between IPCC Assessment Reports — using AR4 values (CH₄ = 25) instead of AR6 (CH₄ = 27.9) understates methane's impact by 10%
• Neglecting to specify the time horizon — GWP100 and GWP20 give very different results for short-lived gases; always state which time horizon was used

How to Interpret Results

• If a small mass of fluorinated gas produces a large CO₂e value, this reflects the gas's extreme radiative efficiency — replacing it with a low-GWP alternative can yield outsized emission reductions
• When methane dominates your CO₂e total despite being a small fraction by mass, prioritize leak detection and repair programs — methane reductions have an amplified impact due to the GWP multiplier
• Compare the CO₂e contributions of different gases to identify which gas type offers the greatest reduction opportunity relative to abatement cost

Frequently Asked Questions

Why use GWP100 instead of GWP20?

GWP100 is the standard for regulatory compliance and most reporting frameworks (GHG Protocol, UNFCCC). GWP20 gives more weight to short-lived gases like methane (GWP20 = 81.2 vs GWP100 = 27.9). Some researchers advocate for GWP20 to emphasize near-term warming impacts, particularly for methane reduction policies.

What is GWP* and how is it different?

GWP* is an alternative metric that better represents the warming impact of short-lived climate pollutants like methane. While GWP treats a pulse emission as equivalent regardless of whether it is new or sustained, GWP* accounts for the change in emission rate. This is an emerging metric not yet widely adopted in regulations.

Which IPCC Assessment Report GWP values should I use?

Use the values required by your reporting framework. Most current frameworks (CDP, SBTi) accept or require IPCC AR5 or AR6 values. The UNFCCC still uses AR4 values for national inventories under the Kyoto Protocol. AR6 (2021) values are the most up-to-date: CH₄ = 27.9 (fossil) or 27.2 (biogenic), N₂O = 273. Always state which AR values you used for transparency.