Global warming potential
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Global Warming Potential: Analyzing Metrics and Alternatives
Introduction to Global Warming Potential (GWP)
Global Warming Potential (GWP) is a metric used to compare the climatic impact of different greenhouse gases relative to carbon dioxide (CO2). It is widely used under the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC) due to its simplicity and transparency1. However, GWP has faced significant criticism for its formulation and the assumptions it makes about emissions and their impacts4 6.
Criticisms and Limitations of GWP
Mathematical and Conceptual Flaws
The GWP metric has been criticized for its mathematical structure, which can lead to errors when comparing emissions of different greenhouse gases. The unit impulse response functions used in GWP calculations do not fully represent the relationship between emissions and radiative forcing, leading to inaccuracies4. Additionally, the assumption that greenhouse gas emissions occur as a single pulse is rarely justified in ecosystem studies, making GWP less applicable in these contexts3.
Sensitivity to Uncertainties
GWP calculations are sensitive to various uncertainties, including the atmospheric lifespans of gases and the radiative efficiencies of marginal changes in CO2, CH4, and N2O. These uncertainties can significantly affect GWP values, leading to variations in the metric's accuracy5. For instance, the GWP of methane (CH4) and nitrous oxide (N2O) can vary by up to 20-30% depending on the representative concentration pathways (RCPs) and time horizons considered2.
Proposed Alternatives to GWP
Global Temperature Change Potential (GTP)
Two new metrics, the Global Temperature Change Potential for pulse emissions (GTPP) and sustained emissions (GTPS), have been proposed as alternatives to GWP. GTPP represents the temperature change at a given time due to a pulse emission of a gas, while GTPS represents the effect of a sustained emission change. GTPS has shown to perform well for gases with various lifetimes and offers a more transparent and relevant measure compared to GWP1.
Sustained-Flux Global Warming Potential (SGWP) and Global Cooling Potential (SGCP)
For ecosystem studies, the Sustained-Flux Global Warming Potential (SGWP) and Global Cooling Potential (SGCP) have been introduced. These metrics account for persistent gas fluxes over time, providing a more realistic measure of an ecosystem's climatic role. SGWP is generally larger than GWP for methane and nitrous oxide emissions, highlighting the need for more dynamic and flexible modeling approaches3.
Temperature Proxy Index (TEMP)
The Temperature Proxy Index (TEMP) is another proposed metric that aims to provide a better fit to historical temperature data. TEMP calculations suggest that indices need to be updated progressively with new measurements and advancements in understanding Earth system processes. This metric addresses some of the limitations of GWP by considering the dynamic nature of the climate system8.
Future Changes and Implications
Impact of Future Greenhouse Gas Concentrations
Future changes in greenhouse gas concentrations will alter GWPs due to climate-carbon cycle feedbacks and changes in atmospheric residence times. For example, the 100-year GWP of methane could increase by up to 20% under the lowest RCP by 2100, while the GWP of nitrous oxide could increase by more than 30% under the highest RCP2. These changes highlight the need for continuous evaluation and potential revision of GWP values.
Policy and Climate Goals
The choice of metric can significantly impact climate policy and the emphasis placed on reducing different types of greenhouse gases. The widely used 100-year GWP may overstate the importance of short-lived climate pollutants (SLCPs) unless immediate and stringent reductions are made. This underscores the importance of selecting appropriate metrics that align with specific climate goals, such as limiting peak warming9.
Conclusion
While GWP remains a widely used metric for comparing the climatic impacts of greenhouse gases, it has several limitations and is sensitive to various uncertainties. Alternative metrics like GTP, SGWP, SGCP, and TEMP offer more nuanced and potentially more accurate measures of greenhouse gas impacts. Continuous evaluation and adaptation of these metrics are crucial for effective climate policy and achieving long-term climate goals.
Sources and full results
Most relevant research papers on this topic
Alternatives to the Global Warming Potential for Comparing Climate Impacts of Emissions of Greenhouse Gases
The Global Temperature Change Potential (GTPS) is a more robust and transparent alternative to the Global Warming Potential (GWP) for comparing climate impacts of greenhouse gas emissions, with potential for use in the Kyoto Protocol.
Highly CitedFuture changes in global warming potentials under representative concentration pathways
The absolute global warming potential of CO2 decreases under all representative concentration pathways, with smaller decreases for longer time horizons due to increased climate-carbon cycle feedbacks.
Highly CitedMoving Beyond Global Warming Potentials to Quantify the Climatic Role of Ecosystems
Ecosystems' climatic role can be better understood using dynamic modeling approaches that account for temporally variable greenhouse gas exchange.
Highly CitedGlobal Warming Potentials: 2. Accuracy
The Global Warming Potential concept has flaws in its mathematical structure, leading to errors in comparing greenhouse gas emissions changes and highlighting the need for improved methods for assessing climate change impacts.
Highly CitedSensitivity of direct global warming potentials to key uncertainties
The study reveals that uncertainties in global warming potentials (GWPs) can significantly alter the assessment of greenhouse gas effects, with a balanced carbon cycle model, fertilization feedback parameter, and atmospheric lifetime uncertainties contributing to varying GWP values.
A guide to global warming potentials (GWPs)
The proposed alternative GWP index, which considers capital investment duration, shifts focus from short-lived gases like methane to CO2 and reduces uncertainties in atmospheric lifespans and radiative heating effects.
Highly CitedGlobal Warming Potentials: 1. Climatic Implications of Emissions Reductions
GWPs are accurate for short time horizons, but over long time horizons lead to tradeoffs between near-term and long-term climate change effects.
Highly CitedEvaluating Global Warming Potentials with historical temperature
The TEMperature Proxy index (TEMP) better reproduces historical temperature for CH4 than the Kyoto GWPs, but the N2O GWP does not, due to simplifying assumptions and uncertain parameter estimations in the IPCC calculation methodology.
Highly CitedNew use of global warming potentials to compare cumulative and short-lived climate pollutants
The 100-year global warming potential (GWP100) effectively measures the relative impact of both cumulative and short-lived climate pollutants on realized warming 20-40 years after emission, but overstates the importance of current SLCP emissions unless stringent reductions result in temperatures nearing their peak soon after mid-century.
Highly CitedInsensitivity of global warming potentials to carbon dioxide emission scenarios
The global warming potential of carbon dioxide relative to other radiatively active trace gases is nearly independent of the CO2emission scenario, making the concept of the global warming potential useful despite climate system nonlinearities and uncertainties.
Highly Cited