Global warming potential (GWP) and how it's calculated

GWP is a fundamental component of carbon accounting, providing the necessary methodology for quantifying and comparing greenhouse gas emissions . GWP is used to aggregate emissions into a single metric (CO2e or carbon dioxide equivalents), which simplifies reporting and helps in setting and achieving reduction targets. But how are they calculated, and which gases have GWP values?

What is global warming potential?

Global Warming Potential - also known as GWP - is a measure used to compare the ability of different greenhouse gases to trap heat in the atmosphere, contributing to global warming. It's a way of quantifying the impact of different gases relative to carbon dioxide (CO₂), which is the most common greenhouse gas. 

GWP is crucial in climate policy and environmental science, as it helps policymakers and scientists compare and prioritize efforts to reduce emissions of various gases.

How is GWP calculated?

The calculation of Global Warming Potential (GWP) involves a few key steps and considerations. GWP is a measure used to compare the impact of different greenhouse gases on global warming, by quantifying their ability to trap heat in the atmosphere relative to carbon dioxide (CO2). Here's an overview of the process:

Time horizon

GWP is calculated over a specific time period, commonly 20, 100, or 500 years. This is because different gases remain in the atmosphere for different lengths of time and have varying degrees of impact over those periods.

Radiative efficiency

The calculation begins with assessing the radiative efficiency of a greenhouse gas. This involves determining how effectively a gas absorbs energy (heat) and then re-emits it back toward the Earth. The more efficient a gas is at trapping heat, the higher its radiative efficiency.

Atmospheric lifetime

The next step is to consider the atmospheric lifetime of the gas, which is the average time a molecule of the gas will stay in the atmosphere before being removed by chemical reactions or other processes. A longer lifetime means the gas can exert its warming effect for a more extended period.

The radiative efficiency and the atmospheric lifetime are integrated over the chosen time horizon. This essentially means calculating the total energy absorbed by a certain amount of the gas over the specified period.

Comparison to CO2

The final step is to compare this integrated impact to that of CO2, which is the reference gas with a GWP defined as 1. The GWP of the greenhouse gas in question is the ratio of the total heat trapped by a certain mass of the gas to the total heat trapped by the same mass of CO2 over the same period.

Sometimes, indirect effects like the gas’s impact on ozone or cloud formation are also considered, but this is more complex and not always included in standard GWP calculations.

It's important to note that GWP values are approximations and are periodically updated as scientific understanding evolves. They are critical tools in climate policy for comparing and prioritizing the reduction of emissions from various greenhouse gases.

Understanding greenhouse gases

Understanding greenhouse gases is pivotal to addressing the challenges of global warming. Greenhouse gases (GHGs) are the primary drivers of climate change, each contributing uniquely to the Earth's warming - here are some examples of those gases: 

To effectively manage and reduce these emissions, frameworks like the Greenhouse Gas Protocol (GHG Protocol) have been established. The GHG Protocol, developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD), provides standardized measurement and management strategies for GHG emissions. 

This protocol, along with efforts from other international bodies such as the Intergovernmental Panel on Climate Change (IPCC) and the United Nations Framework Convention on Climate Change (UNFCCC), underpins the global response to climate change. These organizations play a crucial role in guiding policies, reporting standards, and mitigation strategies, shaping our collective understanding of greenhouse gases and their impact on global warming.

For a more comprehensive list of all gases considered with GWP, see the Greenhouse Gas Protocol’s list of Global Warming Potential values.

Limitations of GWP

Despite its widespread use, Global Warming Potential (GWP) has several limitations that are important to consider. Firstly, GWP simplifies the complex interactions of various gases in the atmosphere by converting their impacts into a single metric relative to CO2. This can sometimes overlook the nuances of how different gases behave over time, particularly since GWP values are calculated for specific time horizons (like 20, 100, or 500 years), which may not fully capture the long-term or short-term effects of these gases. 

Moreover, GWP does not account for indirect effects of greenhouse gases, such as their influence on cloud formation or the albedo effect (reflection of solar radiation). GWP calculations often have a degree of uncertainty due to variations in atmospheric models and assumptions used in their computation. This can lead to debates over the most accurate GWP values for certain gases, potentially impacting climate policy and emission reduction strategies. 

It’s also worth noting that focusing solely on GWP might oversimplify climate mitigation efforts, as it doesn't encompass other crucial factors such as the rate of emission, geographic source, or the socio-economic impacts of reducing certain emissions. While GWP is a useful tool for comparing the relative climate impacts of different gases, it should be used in conjunction with other considerations in comprehensive climate science and policy analysis.

While GWP may have its limitations, it’s still a great indicator of the most potent gases that are contributing to global warming - and therefore are a good direction for organizations to prioirtize their operational changes to reduce their emissions.

How Minimum can help

Minimum can help organizations to understand their existing carbon output, and create plans to mitigate climate related risks in the future.  Our Emissions Data Platform seamlessly collects and processes emissions data from every corner of your organization and supply chain - no matter the format. Making it the ideal platform for emissions audits and all-round business intelligence. 

Learn more about how Minimum's Emission Data Platform can help to power you all the way to Net Zero today.