An Integrated Global Greenhouse Gas Information System (IG3IS)

Atmospheric composition measurements in the latter half of the twentieth century showed increasing global concentrations of greenhouse gases. These measurements were the initial cause of concern about global warming and climate change. Today, as nations make pledges to reduce their greenhouse gas (GHG) emissions, concentration measurements of carbon dioxide (CO2) and other GHGs will unequivocally determine whether the actions taken are having the desired effect.  Thus, WMO has initiated the development of an Integrated Global Greenhouse Gas Information System (IG3IS) to help guide valuable GHG emission-reduction actions in response to climate change. This new System will establish and build confidence in the role of atmospheric composition measurements as an essential part of climate change mitigation efforts. This article discusses the need for and development of atmospheric composition measurements and the role of IG3IS.

Climate change a global concern

In 1992, participants of the United Nations Conference on Environment and Development (the “Rio Earth Summit”) adopted the United Nations Framework Convention on Climate Change (UNFCCC), an international treaty aimed at combatting climate change. The ultimate objective of the Convention is to stabilize greenhouse gas (GHG) concentrations "at a level that would prevent dangerous anthropogenic (human-induced) interference with the climate system." It further states "such a level should be achieved within a time frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner." There are now 197 Parties to the Convention. But, what was the motivation and basis for this impressive global action?

The UNFCCC was established upon a bedrock of scientific evidence and understanding, consisting particularly of long-term observations of Earth’s atmospheric chemical composition and its change over time. Consistent and accurate measurements show rapidly rising concentrations of GHGs, such as carbon dioxide. These measurements also unambiguously attribute the rise to human activities, and link the increasing GHG concentrations to global warming and negative climate impacts.1

Since the eighteenth century Industrial (or energy) Revolution, human activities have caused a steady increase in concentrations of GHGs such as CO2, methane (CH4) and nitrous oxide (N2O), and mean global temperatures have been rising in response. Concentrations of CO2 have risen by more than 40% from pre-industrial levels and continue to rise at an increasing rate. They are now higher than they have been in at least about four million years, when global average temperatures were 2 to 3 °C hotter than in the nineteenth century and sea levels were 7 to 25 metres higher than today.2 Current levels of CH4 are 2 ½ times the pre-industrial value, and after a number of years of stability, CH4 concentrations are rising again. As a direct consequence of these changes to atmospheric composition, global average temperatures are rising rapidly. WMO recently announced that the global average temperature in 2016 was about 1.1 °C higher than the pre-industrial period. It was approximately 0.83 °C above the long term average (14 °C) of the WMO 1961-1990 reference period, and about 0.07 °C warmer than the previous record set in 2015.

Globally averaged surface mole fractions of carbon dioxide and methane and their growth rates calculated from in situ network of the GAW Programme.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) released its Fifth Assessment Report (AR5), the first volume of which reports on the physical science basis of climate change. The categorical conclusion is that climate change is real, human activities are the cause, and negative impacts on society, such as sea-level rise, are rapidly mounting. For the first time, IPCC was also able to estimate cumulative CO2 emissions since pre-industrial times and provide a CO2 budget for future emissions to limit warming to less than 2 °C.  About half of this budget was already emitted by 2011.

In December 2015, the UNFCCC adopted the Paris Agreement on climate change. Its goal is to keep global temperature rise by the end of the century well below 2 °C above pre-industrial levels, and to pursue efforts to limit the temperature increase even further to 1.5 °C. Global levels of CO2 had increased by 12% from 356 ppm in 1992 when the UNFCCC was adopted to 400 ppm in 2015. In the same period, CO2-eq (for any quantity and type of GHG, the amount of CO2 which would have the equivalent global warming impact) grew by 13% from 421 ppm to 485 ppm. Due to the cumulative effect of GHGs in the atmosphere, the window of opportunity to meet the Paris Agreement objectives is closing very fast.3

The Paris Agreement intends to achieve its goal via “nationally determined contributions” (NDCs) that vary by national capability and level of economic development. Several independent estimates suggest that the current sum total of all emission reduction pledges under current NDCs does not put the world on a pathway to achieve the goals of the Paris Agreement. The structure of the agreement takes this initial gap into account by incorporating a periodic “global stocktake” every five years beginning in 2018, with the intent of tracking global progress towards achieving the aforementioned goals. This will also be a time for nations to take stock of their individual progress and a chance to help close the gap by increasing their pledges. But, how will progress toward Paris Agreement goals be determined?

Cape Point, South Africa, GAW Station

Atmospheric measurements to manage emissions

The best indicator of the success and vitality of the Paris Agreement are the very measurements of atmospheric concentrations of CO2 and other GHGs that stimulated action on climate change. Continuous, consistent, and accurate GHG concentration measurements at local, national, and global scales have value beyond their original role as the harbinger calling attention to the climate change challenge. Measured GHG concentrations are the ultimate indicators of emission reduction policy successes. Regardless of the GHG emission reduction policies and measures applied, effective implementation, both in the short- and long-term, will require consistent, reliable and timely information on the magnitude of GHG concentrations, their sources and sinks, and their trends over time.  For the global stocktake to have its desired effect, a global goal for average GHG concentrations in the 2030-to-2050 timeframe must be established, translated into specific emission reduction efforts and updated periodically. GHG concentrations and their trends over time are the ultimate way for individual governments to clearly gauge whether their nationally-determined actions are adding up to the desired global outcomes.

The Global Atmosphere Watch (GAW) Programme of WMO was established in 1989 in recognition of the need for improved scientific understanding of the increasing influence of human activities on atmospheric composition and subsequent environmental impacts. GAW measurements of ozone-depleting gases have played and continue to play a critical role in the successful response of the Montreal Protocol to stratospheric ozone depletion and the increase of ultraviolet (UV) radiation. GHG measurements from GAW are recognized by the Global Climate Observing System as a key component of its implementation plan under the UNFCCC. Historically, GHG measurements have been made in remote locations that optimized the sampling frequency of global background concentrations. In 2016 GAW launched a new implementation plan built on the concept of “science for services” and bringing an increased user orientation to the programme.

UNFCCC has required that certain countries report their annual GHG inventories. These inventory reports have been produced according to the statistical methods outlined in the 2006 Guidelines of the IPCC Task Force on National Greenhouse Gas Inventories (IPCC TFI). In 2010 the atmospheric, carbon cycle and climate change science communities produced a number of studies on the potential for atmospheric GHG concentration measurements and model analyses to independently evaluate and improve the accuracy of GHG emission inventories. These studies concluded that a realization of this approach would require additional investment in research, increasing the density of well-calibrated atmospheric GHG measurements and improving atmospheric transport modelling and data assimilation capabilities.

GAW science for services: IG3IS

The Seventeenth World Meteorological Congress passed a resolution initiating the development of an Integrated Global Greenhouse Gas Information System (IG3IS), based on GAW successes and progress in atmospheric measurements and modeling since 2010. A planning team comprised of scientists and stakeholders from developed and developing countries in all six WMO regions was established to develop the IG3IS Concept Paper. IG3IS will work closely with the inventory builders and other stakeholders who need to track GHG emissions to develop methodologies for how atmospheric GHG concentration measurements (the top-down) can be combined with spatially and temporally explicit emission inventory data (the bottom-up) to better inform and manage emission reduction policies and measures. GAW GHG measurement network and standards will be essential for IG3IS success, but the focus, and location of measurement sites, must expand from remote locations to key GHG source regions where emission reduction is taking place or is needed.

IG3IS will focus on existing-use cases for which the scientific and technical skill is proven and on where IG3IS information can meet the expressed (or previously unrecognized) needs of decision-makers who will value the information. The ultimate success criteria are that the IG3IS information is “used” and guides valuable and additional emission reduction actions, building confidence in the role of atmospheric composition measurements as an essential part of the climate change mitigation tool kit.

The success of IG3IS will depend on international coordination of WMO Members and collaborations with a number of WMO partners such as the United Nations Environment Programme, the International Bureau of Weights and Measures, the Group on Earth Observations, the IPCC and many others. IG3IS will establish and propagate standards and guidelines for methods that produce consistent and intercomparable information, such as those GAW already produces, for concentration measurement standards. Over time, the IG3IS framework must be capable of promoting and accepting advancing technical capabilities (for example, new satellite observations and sensors), continually improving the reach and quality of the information and increasing user confidence.

IG3IS implementation is now underway following the endorsement of the Concept Paper by the WMO Executive Council in June 2016. The IG3IS team defined four implementation objectives, the first three being: 1) reduce uncertainty of national emission inventory reporting to UNFCCC; 2) locate and quantify previously unknown emission reduction opportunities such as fugitive methane emissions from industrial sources; and 3) provide subnational entities such as large urban source regions (megacities) with timely and quantified information on the amounts, trends and attribution by sector of their GHG emissions to evaluate and guide progress towards emission reduction goals.

The fourth IG3IS objective is similar in nature and scope to objective 3), but is focused on support for the Paris Agreement’s global stocktake. It will by necessity be implemented at national and global scales, but it is less mature than the other three objectives at this time. One reason is that although IG3IS has a vision for how to support stocktaking, the Paris Agreement does not specify how the global stocktake will be conducted. Another reason is that accounting for fossil fuel CO2 via top-down methods lack the maturity to match the accuracy of IPCC TFI Tier 3 protocols for estimating fossil fuel CO2 emission inventories at the national scale. This is because atmospheric measurements of CO2 contain a significant biospheric signal and are therefore necessary, but not sufficient, to infer fossil fuel CO2 emissions.4 However, it has been demonstrated that fossil fuel CO2 emissions can be inferred by inverse model analyses of a combination of atmospheric CO2, radiocarbon (14CO2) measurements, together with measurements of other co-varying atmospheric species.5

IG3IS implementation is proceeding along two lines of activity:

  • The preparation of methodological guidelines that describe “good practice” use of atmospheric measurements for implementation under each objective area and
  • The initiation of new projects and demonstrations that propagate and advance these good practice capabilities and build confidence in the value of IG3IS information with stakeholders.

Objective 1 – support of national GHG emission inventories

Prior to the Paris Agreement, the UNFCCC required the Annex 1 (developed) Parties submit annual country reports containing their national emission inventories, but Non Annex 1 (developing) Parties did not have this requirement. Now, Article 13 paragraph 7 of the Paris Agreement states:

Each Party shall regularly provide the following information: (a) A national inventory report of anthropogenic emissions by sources and removals by sinks of greenhouse gases, prepared using good practice methodologies accepted by the Intergovernmental Panel on Climate Change and agreed upon by the Conference of the Parties serving as the meeting of the Parties to this Agreement.

The “good practice methodologies” referred to in the Paris Agreement are the protocols developed by the IPCC TFI. These combine source-specific emission factors with statistical activity data, for example, the number and type of coal burning plants or cars on the road – bottom-up methods. Emissions of carbon dioxide from the use of homogenous fossil fuels and predictable processes can be estimated accurately where well-developed statistical systems are present, but other more heterogeneous and dispersed sources such as methane from waste management and natural gas production and pipeline transmission are more difficult.

Atmospheric measurements and model analyses can support the process by providing the useful additional constraint of top-down quantification (where the fluxes are estimated through inverse modelling of observed concentrations). Switzerland and the United Kingdom, and to a lesser extent Australia, already make use of top-down analyses to guide improvements to their bottom-up emission inventory reporting. An IG3IS near-term objective is to propagate these good practices and establish quality metrics for these top-down methods, how they can be compared to GHG inventories developed from bottom-up methodologies, and how the results can be used to target improvements in bottom-up inventory data inputs. Progress on this objective is evident in the approved outline for the “2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.” It will update and elaborate the IPCC TFI Guidelines to include the use of atmospheric measurements and model analyses based on the abundant new scientific and empirical knowledge published since 2006.

Objective 2 - Detection and quantification of fugitive methane emissions

Global atmospheric concentrations of methane continue to increase, but the global growth rate’s variability and attribution to both natural and anthropogenic sources are not well understood. Natural gas, composed mostly of methane, has the potential to be a far more climate-friendly energy source than coal or oil. But the problem with methane is that if it gets into the atmosphere without being burned it becomes a very potent GHG — much more potent, molecule-to-molecule, than carbon dioxide.

The amount and location of “fugitive” methane emissions from industrial and agricultural sources are not well understood. This IG3IS objective intends to extend the significant successes of the Environmental Defense Fund and National Oceanic and Atmospheric Administration in detecting methane super-emitters in the North American oil and gas supply chain worldwide.6,7 Such information, if acted upon, could lead to significant methane emissions reductions. Exploring these solutions and applying them to new types of sites or emissions profiles – for example offshore platforms – can potentially provide further reductions. IG3IS also intends to extend these approaches to other methane-emitting sectors such as flooded lands, agriculture, landfills and wastewater, and develop sector-appropriate methodologies in the medium term. These sectors have close links with urban emissions as they are much more likely to be located in or closer to cities than oil and gas extraction sites.Research studies have shown that a 50/5 rule applies to natural gas leaks. That is, the largest 5% of leaks are typically responsible for more than 50% of the total volume of leakage. These "super-emitters" – large point sources thought to contribute disproportionately to anthropogenic methane emissions – are logical mitigation targets.

A tiered observing strategy, involving satellite, aircraft, and mobile and tall tower surface measurements, has proven to be effective in identifying these super-emitters and their contribution to regional methane emissions. This approach has been demonstrated with field studies of agricultural and oil and gas sources in California's San Joaquin Valley with the cooperation of a multi-stakeholder team.9

Dr. Gaby Petron with her mobile GHG measurement laboratory studying methane leakages. Fugitive super-emissions of methane can be tracked down with a tiered suite of observations made from satellites, aircraft and surface-based vehicles and tall-towers that can successively zoom-in from a regional-scale down to a leak’s location within a facility.

Objective 3 - Estimation and attribution of megacities emissions

The Lima–Paris Action Agenda of the Paris Agreement has formalized a role for sub-national entities such as cities (large urban source regions). Cities and their power plants are the largest sources of GHG emissions from human activity. In order to provide a diagnosis of urban emissions at scales relevant to urban decision-making and enable identification of low-carbon or carbon mitigation opportunities, cities need better information about their emitting landscape. Such information should not only reflect scientifically accurate methods, but place emissions at space and time scales relevant to urban decision-making and identify key functional characteristics (sector, sub-sector, fuel).

A number of research projects around the world, such as the Indianapolis INFLUX study and the Los Angeles/Paris Megacity Project, have developed and tested methods for estimation of GHG emissions. This work has established an urban GHG information system that combines atmospheric monitoring, data mining and model algorithms. IG3IS will redesign this information system to be deployable to different parts of the world, particularly in the low- and middle-income countries where GHG information needs are greatest and capacity is limited.

Several studies have shown the potential to better quantify the GHG emissions and trends of cities with atmospheric measurement networks and high-resolution inverse model analyses.10,11 The requirements for atmospheric inversion are more demanding in the case of fossil fuel CO2. However, there is evidence that by combining inverse model analysis of a sufficiently dense and well-distributed network of measurements with spatially explicit prior knowledge of sources, urban emissions of fossil fuel CO2 can be better quantified.12

While trends in total emissions of fossil fuel CO2 from cities are valuable, city planners and managers will need sector-specific information to guide them to emission reduction opportunities. In emerging economies that may have inadequate bottom-up statistical knowledge of emissions for their national area, large urban source regions and forested landscapes, the IG3IS top-down atmospheric measurement inversion approaches can prove to be especially valuable sources of baseline and trend information.

Total flux estimates over a 30-day period, for four 6-hour periods, for anthropogenic emissions (red), biogenic fluxes (green) and the total (blue). The prior estimates are shown as open rectangles, while the posterior is shown as filled rectangles. Uncertainty reduction is evident for the morning and afternoon time periods.13

IG3IS - Providing carbon situational awareness

Earth’s carbon-climate system is undergoing profound and unprecedented change. This change is driven by fossil fuel and land-use change emissions that increase atmospheric concentrations of CO2 and other GHGs. During the last decades, the effect of emissions on the increase of atmospheric CO2 has been strongly attenuated by the response of the natural carbon cycle, with ocean and land carbon sinks absorbing on average approximately half of the emissions. Future climate change is projected to weaken the capacity of natural sinks, that is diminish their capacity to absorb CO2. This combination of complexity across many space-time scales and controlling processes has some parallels with well-established weather and other environmental extremes. However, unlike weather and extreme events, society currently has limited "situational awareness" of the coupled human-natural carbon system.

While IG3IS has near-term objectives and deliverables that will guide improved knowledge on emissions and potentially inform new emission reduction opportunities, the long-term payoff is to enable the provision of decision-relevant carbon situational awareness through comprehensive, reliable, sustained, frequent assessments of greenhouse gas fluxes.

The long-term vision for IG3IS capabilities is similar in some respects to aspects of modern weather services – primarily the rapid delivery of current and recent carbon fluxes and controlling activity (on timescales of weeks rather than years). As with modern weather services, the transition between research-driven and operational GHG observing and information systems presents a number of challenges and will be decades in the making.

A study sponsored by the European Commission examined the requirements for an operational observing system able to monitor fossil fuel CO2 emissions.  This was primarily focused within the European domain and built upon the investments already made in the Copernicus programme. The report’s conclusions are relevant to the gap-filling investments that are necessary for the IG3IS approach to provide additional valuable constraints on fossil fuel CO2 emission inventories, and on the long-term IG3IS goal of a more systematic operational approach. IG3IS will build upon, integrate and improve existing and planned surface-based measurement networks, airborne and satellite observations, modelling frameworks and data assimilation systems and where necessary, fill key gaps in those systems. 

As the providers of the modern weather services, WMO, its Members and partners have the experience and technical knowledge essential for building the IG3IS and sustaining it in its future construction, deployment and operational phases. By leveraging existing skills from weather services and ongoing atmospheric and carbon cycle research, WMO can provide the leadership and structure needed to support the building of an IG3IS capable of delivering decision-relevant situational awareness for society, as it attempts to manage the unavoidable – and avoid the unmanageable – impacts of climate change.


The Swiss Top-Down Analyses

The spatial distribution of the prior emission inventory for Switzerland is shown in (a), posterior emissions are shown in (b), and absolute and relative difference (posterior minus the prior) are shown in (c) and (d), respectively. An irregular inversion grid was used that exhibits high spatial resolution close to the observation sites (marked by X) and becomes coarser with distance from these sites.8

Continuous methane measurements from four sites on the Swiss Plateau and two additional sites were combined with atmospheric transport simulations and an inverse modeling framework to deduce the spatial distribution of CH4 emissions in Switzerland and adjacent countries. The best inverse estimate (a posteriori) of total Swiss CH4 emissions for the observation period March 2013 to February 2014 is 196±18 Gg yr–1.

This value is in close agreement with the bottom-up (a priori) national emission inventory total of 206±33 Gg yr–1 reported by Switzerland to UNFCCC in 2015 for the years 2012 and 2013.

The top-down approach largely confirms the bottom-up estimate of emission totals, but the inclusion of atmospheric measurements reduces the uncertainty on the reported value from 16% to 9%. The measurement and inversion system was set up to estimate the spatial distribution of total emissions and not to attribute emissions to specific and separate source sectors.

A robust spatial pattern can be seen in the plots of the absolute and relative difference of the a posteriori minus a priori emissions and suggests increased methane emissions for northeastern Switzerland. A possible cause for these differences is farming practices between this area and the rest of the country, resulting in different per-head emissions from livestock.

Other potential anthropogenic and natural sources may contribute to the unexpectedly high emissions from this area. Further observations are needed to verify and better characterize this source, but the result already demonstrates added value.


Phil DeCola, Sigma Space Corporation and Department of Atmospheric and Oceanic Sciences, University of Maryland

Oksana Tarasova, Chief, Atmospheric Environment Research Division


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13 Ciais et al., 2015: Towards a European Operational Observing System To Monitor Fossil CO2 Emissions (

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