Greenhouse gases such as carbon dioxide, methane and nitrous oxide, absorb and emit radiant energy within the thermal infrared spectrum. By absorbing and re-emitting energy, these gases act like a blanket, insulating the Earth and slowing down the rate at which energy can escape into space. By trapping this energy in the Earth’s atmosphere, these gases cause what is known as the greenhouse effect or global warming. But major greenhouse gases have different ‘warming potentials’ of the Earth according to the ability of each greenhouse gas to absorb energy (its radiative efficiency) and how long the gas remains in the atmosphere.
The Global Warming Potential or GWP, is a common unit of measurement that allows scientists to compare the impact of different greenhouse gases. The Global Warming Potential system measures the amount of energy the emissions of 1 ton of a greenhouse gas will absorb over a period of time (usually 100 years), relative to the emissions of 1 ton of carbon dioxide. The higher the GWP, the more a gas warms the planet in comparison to carbon dioxide over that same period. The GWP system allows analysts to calculate emissions estimates of the different greenhouse gases in order to compile a greenhouse gas inventory. This data gives policymakers the information they need to compare emission reduction strategies across industries.
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Which Greenhouse Gas has the Most GWP
A variety of gases contribute to global warming with two key characteristics of atmospheric gases determining their ‘warming potential’ – the power of the greenhouse effect.
The first characteristic is the ability of the greenhouse gas to absorb energy – its radiative efficiency. The second is the atmospheric lifetime of the gas – the period the gas stays in the atmosphere before natural processes begin to remove it.
A measure of the radiative effect of each unit of gas by weight, over a specified period, expressed relative to the radiative effect of carbon dioxide are the characteristics used to measure the GWP. Based on this calculation, gases with a high GWP are gases that will warm the Earth greater than the equivalent amount of carbon dioxide over the same period. A gas with a long lifetime, but relatively low radiative efficiency, could end up exerting more warming influence than a greenhouse gas that leaves the atmosphere at a quicker rate over the same period of time – and is reflected in a higher GWP.
Although carbon dioxide has a comparatively low GWP, the large increase in CO2 concentrations in our atmosphere as a direct result of human activity, is the major contributor to global warming. The impact of methane on global warming is also becoming clearer. Whilst methane has a relatively low GWP compared to several other greenhouse gases, methane emissions are growing faster now than at any other time in history. Scientists report that current concentrations are now 260% of pre-industrial levels with human-caused methane emissions now responsible for nearly 45% of current net warming
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Global Warming Potentials: Major Greenhouse Gases
Carbon Dioxide
C02 has a GWP of 1. This number stays the same regardless of the time period analyzed. This number is consistent because it is the gas that is used as reference for the GWP [ref].
Methane
Methane or CH4, has been estimated to have a GWP of between 27 – 30 over a period of 100 years. Today, the CH4 emitted into the atmosphere can last a decade which is less time than C02.
However, CH4 absorbs more energy than that of CO2 and the effect of the shorter lifetime combined with the higher absorption of energy is shown in the GWP [ref].
Nitrogen Oxides (N0x)
Nitrous Oxide or N20, has a GWP over 273 times higher than that of CO2 for a 100 year time period [ref].
N20 stays in the atmosphere for an average of 114 years before being removed through chemical reactions or destroyed by a sink [ref].
Sulphur Oxides (SOx)
Sulfur Hexafluoride or SF6 is the greenhouse gas with the highest GWP while Chlorofluorocarbons (CFCs), Hydrofluorocarbons (HFCs), Hydrochlorofluorocarbons (HCFCs) and Perfluorocarbons (PFCs) are also known as high-GWP gases. This is because given the amount of mass these major greenhouse gases have, they trap substantially more heat than C02 and other greenhouse gases. These gases can be in the thousands or tens of thousands in the GWP calculation [ref].
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The Fluorinated gases have the highest GWP as they have the longest atmospheric lifetime, which means it will take many years to see a noticeable decline in the current concentrations we see today.
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Why do GWPs change over time?
There are a variety of factors that influence the change or revision of GWPs. This includes new estimates of the lifetime of each greenhouse gas, impulse response functions, radiative efficiency and amendments to the inclusion of indirect effects and strength have also contributed to the revision of GWPs over the years.
As carbon dioxide is the reference point for GWPs, it will always remain a 1 however, changes in the understanding of the global warming impacts of CO2 will result in changes to the GWP of all other greenhouse gases as well [ref].
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Is there another way to measure and compare greenhouse gases?
The United States mostly uses the 100 – year GWP as a measure of the impact of different greenhouse gases. But the scientific community has also developed a variety of metrics that could be utilized when comparing greenhouse gases and their impact.
These alternative metrics could differ based on the climate endpoint measured, method of calculation or the timeframe used in the measurement. In some instances, the 20 year GWP is used over the 100 year GWP. The 20 year GWP prioritizes gases that have a shorter lifetime as the calculation doesn’t take into consideration the impact that could occur more than 20 years after the emission.
Another metric that is used is the Global Temperature Potential or GTP. The GWP measures the heat absorbed over a period of time due to emissions of greenhouse gas while the GTP is a measure of the temperature change at the end of that period of time – also relative to carbon dioxide. In contrast to the GWP, the GTP is a more policy-relevant metric that quantifies the temperature impact of a pulse of gas relative to the temperature impact of a pulse of carbon dioxide with equal mass, both evaluated at an endpoint time horizon [ref].
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Global Emissions Monitoring Solutions
We are able to accurately measure the Global Warming Potential of greenhouse gases but it is equally important to monitor greenhouse gas emissions as close to real time as possible. The sustained, routine global monitoring of greenhouse gas concentrations and fluxes is imperative to help us understand global warming and climate change and to provide the evidence base to support emissions mitigation policies and strategies..
GHGSat provides accurate, reliable and cost-effective monitoring of global greenhouse gas emissions. Our cutting-edge technology uses high-resolution satellites that can pin-point methane emissions down to individual facilities. GHGSat combines our industry-leading satellite data with measurements from aerial surveys and recognised third-party datasets, to create customized, actionable emissions intelligence.
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Technology in the fight against climate change
Emissions intelligence empowers carbon intensive industries and governments to achieve their emission reduction goals. GHGSat launched a free version of its emissions intelligence platform, SPECTRA. This service includes an upgraded version of GHGSat’s methane map, as well as access to a gallery of samples of methane measurements from GHGSat and other satellites.
