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How does CO2 compare to other greenhouse gases in terms of global warming potential?
Executive Summary
Carbon dioxide (CO₂) is the baseline greenhouse gas and the dominant driver of long‑term climate change in absolute terms because it is by far the most abundant and long‑lived gas, but per kilogram it has a much lower warming potency than gases like methane, nitrous oxide, and many fluorinated gases; CO₂’s Global Warming Potential (GWP) is defined as 1 and other gases are expressed relative to it [1] [2] [3]. Policymaking and accounting use time horizons (commonly 20‑, 100‑, and 500‑year GWPs) that change comparative rankings: methane is dozens of times more potent than CO₂ over shorter horizons while fluorinated gases can be thousands to tens of thousands of times more potent, and CO₂’s long atmospheric lifetime means its cumulative emissions shape century‑scale warming even if its per‑unit GWP is low [4] [5] [6].
1. Why CO₂ is both the reference and the long‑game climate driver
CO₂ is assigned a GWP of 1 and thus serves as the yardstick against which all other greenhouse gases are compared; this convention appears across technical guidance and public summaries and underpins carbon‑equivalent accounting used by national inventories and policy frameworks [2] [1]. Because CO₂ accumulates in the atmosphere and remains for centuries, its cumulative emissions determine long‑term warming; multiple sources emphasize that while other gases can be more potent per unit, the sheer volume of CO₂ from fossil fuels, industry, and land‑use change makes it the largest contributor to observed warming trends and to increases in the atmospheric greenhouse effect since pre‑industrial times [7] [8]. This dual role—low per‑kilogram potency but large cumulative force—is why CO₂ reduction is central to long‑term climate stabilization strategies [7] [3].
2. Methane: a short‑term heavyweight that shifts with the clock
Methane (CH₄) is substantially more potent than CO₂ on a per‑mass basis, with GWP values that vary by time horizon—roughly ~80–84× over 20 years and ~27–30× over 100 years in contemporary assessments—meaning methane cuts deliver relatively rapid near‑term cooling benefits compared to CO₂ cuts [4] [9]. Sources stress that methane’s atmospheric lifetime is much shorter than CO₂’s, so its climate forcing declines faster after emissions stop; this dynamic makes methane a key target for near‑term temperature management even though it does not replace the need for deep CO₂ reductions to avoid long‑term warming [9] [4]. Accounting choices—whether to use a 20‑year or 100‑year GWP—affect policy priorities and reported CO₂‑equivalent emissions, so the selected time horizon shapes whether methane appears proportionally larger or smaller [9] [4].
3. Nitrous oxide and fluorinated gases: small volumes, outsized potency
Nitrous oxide (N₂O) is roughly ~270–300 times more potent than CO₂ over common GWP horizons, and synthetic fluorinated gases (HFCs, PFCs, SF₆) can have GWPs in the hundreds to tens of thousands range, meaning a kilogram of these gases traps far more heat than a kilogram of CO₂ [4] [5]. Although these gases occur in much smaller global quantities than CO₂, their high per‑unit potency and, in some cases, long atmospheric lifetimes make them critical in targeted mitigation—especially because some fluorinated gases are used in industrial applications where leaks can be prevented and substitutes exist [5] [6]. Policymakers therefore balance reducing CO₂ at scale with regulatory controls on high‑GWP gases to capture “low‑hanging fruit” for rapid emissions reductions [2] [6].
4. Different metrics, different stories: GWP choice matters
The commonly used GWP100 (100‑year horizon) is a political and technical compromise; switching to GWP20 amplifies short‑lived climate forcers like methane, while longer horizons emphasize long‑lived gases like CO₂. Sources document significant variation in reported GWPs across institutions and updates—methane’s 100‑year GWP is reported around 27–30 in recent guidance, whereas earlier figures and alternate accounting conventions produce different numbers and adjust for methane’s oxidation to CO₂ [9] [4]. These methodological choices influence national inventories, corporate carbon‑accounting, and policy narratives: advocates of rapid near‑term temperature limits favor shorter horizons to prioritize methane cuts, while long‑term stabilization frameworks emphasize CO₂ reductions under longer horizons [9] [7].
5. Putting potency and prevalence together: what drives policy priorities
CO₂ is both the largest share of human‑caused emissions and the primary driver of long‑term temperature rise—multiple assessments report CO₂ contributes the majority of the net anthropogenic warming and most of the increase in the greenhouse effect since 1990—so scaling down CO₂ emissions is indispensable for meeting long‑term climate goals [8] [7]. Simultaneously, methane, N₂O, and fluorinated gases offer high‑impact, targeted mitigation opportunities because their per‑unit GWP is much higher and, in some cases, easier to abate quickly through leak controls, regulation, and substitutes [4] [5]. Effective climate strategy therefore combines deep, sustained CO₂ reductions for long‑term stabilization with accelerated cuts to high‑GWP and short‑lived gases to limit near‑term warming and buy time for structural decarbonization [3] [2].