There can be little doubt that carbon emissions need to be reduced. It is increasingly evident that the unabated burning of fossil fuels will result in economic, environmental and social upheaval and, over the long term, security of supply makes transitioning to renewables a win-win situation.

While there is widespread agreement for the need to cut emissions, there is much more debate on how to achieve it. The first major international effort was the Kyoto Protocol. Adopted in 1997 and entering into force in 2005, the landmark treaty committed industrialised nations to specific carbon reduction targets, while allowing increases in emissions for developing countries. Although the deal didn’t make the inroads on reducing carbon emissions many were hoping for, it did put climate change firmly on the global agenda.

With Kyoto and its extension period ending in 2020, the international community signed the momentous ‘Paris Agreement’ in late 2015. This is a step up in ambition, aiming to keep global temperature rise ‘well below’ 2 °C and ‘pursuing efforts’ to limit warming to 1.5 °C. It took the diplomatic approach of inviting countries to pledge their own targets and requires that billions in funding is made available to poorer countries to help with their transition to renewables.

Setting targets to cut carbon emissions globally can’t be based on science alone. It is a political and business game too, needing to be realistic while balancing ambition with compromise. There are few black and white questions. What if, for example, a country burns fossil fuels to manufacture products that will be used overseas? Is the producer or consumer responsible for the emissions?

It is these international scale complexities that makes the signing of the Paris Agreement such an achievement. While it is yet to be universally ratified, it succeeds where the Kyoto Protocol failed: in achieving mutual understanding for the need to reduce emissions between the developing East, dominated by India and China’, and the developed West.

However, enforcing these agreements is a significant challenge. The old adage ‘if you can’t measure it, you can’t manage it’ might be clichéd but it does ring true. Tangible progress needs an accurate system of carbon monitoring, where emitters can confidently track progress against internationally agreed targets.

The Paris Agreement states that all countries must disclose accurate data on their emissions, complete with independent reviews on their performance against nationally determined targets. Although meeting these targets isn’t legally binding, reporting on them is. All but the least economically developed countries and some island states have to provide the information at least every two years, and all countries need to review their ambition every five years.

Measuring carbon emissions: the current system

To report on their carbon emissions, each nation currently compiles data based mainly on energy-use. For example, a power station might determine its emissions by multiplying activity data (such as the amount of fuel consumed) with an ‘emissions factor’, a predetermined coefficient for how much carbon dioxide (CO2) a particular activity emits. When totalled together from different sectors, this ‘inventory’ approach provides a figure for national emissions. The problem is that so many variables can influence the result. For example, some power stations might burn fuel more efficiently than others, or have more effective methods of scrubbing the flue gases.

These variables and complexities, when scaled up to national level, can mean that the smallest uncertainty in input data can result in significant inaccuracies in reported emissions. For example, when converted to equivalent emissions, two official datasets for energy use in China – one at national level and one combining provincial data – differed by 1.4 gigatonnes of CO2 in 2010. This difference is equivalent to the entirety of Japan’s – the world’s fourth largest emitter – annual CO2 emissions.

Coupled with these uncertainties, reported emissions only provide annually averaged data on a national scale, making it impossible to track any regional differences or variations over different months and seasons.

It is not just the emissions that needs to be measured: a government might plant new forests to sequester the CO2 it emits, or another might chop down trees to build new power stations. The combination of emissions and land use results in the net emissions for a country. Therefore, as well as calculating direct emissions, the rates of deforestation and forestation must be taken into account, along with a calculation for how much carbon the biomass can sequester.

The simple question of ‘how much carbon dioxide does each country emit?’ therefore results in a very complicated answer. The resulting uncertainties aren’t for a lack of effort or shoddy science. The current system is based on tremendous scientific effort and is robust enough to facilitate the signing of international agreements and enable tangible progress in reducing emissions. Nevertheless, it is far from perfect, and in large parts it relies on a system of trust that lacks independent verification.

As a result, the world’s governments and international bodies are looking for a new approach. If they were to write a wish-list for a new way of monitoring carbon emissions globally, many would probably call for a consistent, independent method that avoids reporting errors, can provide repeatable data and is technologically achievable and costs competitive.

A new approach to an old problem

Satellites, with their global reach and consistent measurements, have for some time been demonstrating their potential to meet these requirements. The European Space Agency pioneered this approach with the launch of Envisat in 2002. Operational for 10 years, Envisat was one of the largest civilian Earth observation platforms ever put into orbit, weighing eight tonnes and carrying a suite of different instruments. One of those, called SCIAMACHY, was an imaging spectrometer designed to map the concentration of CO2 and methane (CH4) globally. While the spatial resolution was too coarse to accurately determine sources of emissions, it demonstrated the potential for using satellites to measure trace gases in the atmosphere.

More recently, the Japanese launched a still-operational satellite called the Greenhouse Gases Observing Satellite (GOSAT) in 2009. As the name suggests, it is specifically designed to measure CO2 and CH4 and offers more accurate and improved resolution when compared to SCIAMACHY. Yet it is not sensitive enough to detect individual ‘point sources’ of emissions – like those from cities or even high-emitting power stations – and is instead intended to improve measurements of the global distribution of CO2 and CH4.

However, the ability for satellites to detect human-induced emissions is beginning to be demonstrated. NASA successfully launched the Orbiting Carbon Observatory-2 (OCO-2) in 2014 after the first version was lost in a failed launch five years earlier. Again, its primary objective is to quantify large scale natural fluxes of CO2, but initial results have detected local point sources of CO2 caused by human activity.

With the technology improving and the need for more accurate monitoring of carbon emissions firmly on the international agenda, there is a raft of new satellites and sensors planned for launch over the next ten to fifteen years. At least four more missions dedicated to monitoring CO2 are planned for launch by 2020, each one offering a range of mission objectives in terms of spatial resolution and precision.

This includes OCO-3, based on the spare parts of OCO-2 and planned to go onto the International Space Station in 2018. A new agile pointing mechanism is being added to the sensor, allowing it to go into a snapshot mode that can be used to focus on measuring emissions from cities and power stations, adding to the capabilities of OCO-2 for detecting regional sources of emissions and demonstrating the potential further.

Challenges ahead

As the amount of data and the accuracy of measurements improves, attention is turning towards how to bring it all together and improve the current system for reporting carbon emissions.

The European Commission has clearly defined its intentions, publishing a detailed roadmap in 2015 setting out its aim to build a full observing system by the 2030s. It envisages a constellation of satellites, alongside improved modelling capabilities and existing data, to provide a comprehensive system that will support the reporting of CO2 emissions for international climate commitments. The roadmap is ambitious and seeing it through will likely cost billions of euros, but it demonstrates the direction of travel international bodies are heading in when it comes to future aspirations.

Even with satellites already demonstrating the technology, there is still a long way to go. Passive spectrometers work by detecting the unique spectral fingerprint of greenhouse gases as sunlight travels through the atmosphere between the Earth’s surface and the satellite’s sensor. Therefore, measurements can only be acquired in daylight and through clear skies, a problem highlighted by the fact that only around 10% of OCO-2’s measurements are sufficiently cloud free to be useable.

Mission proposals have been tabled, such as NASA’s ASCENDS mission, that will use active LIDAR systems to operate day or night, but these are unlikely to be operational much before the mid-2020s. The problem is mitigated somewhat by simply increasing the number of satellites and in doing so increasing the chances of more cloud-free observations, but this in itself adds a new challenge. Any given satellite is likely to provide hundreds of terabytes of data each year; retrieving, storing, assimilating and interpreting data on that scale, from multiple satellites at the accuracy required, becomes a significant challenge.

Furthermore, the atmosphere is dynamic and satellites can only measure the concentration of CO2 in any given column of air. This isn’t enough information to tell you exactly where the emissions came from, or how much was the result of human processes compared to natural variability. A system generating real-time emissions data for any particular region therefore requires accurate atmospheric models, built from a network of in-situ monitoring stations, combined with land use data, existing inventories, and satellite data. Building such a system is part of the European Commission’s ambition, but it will no doubt take years to develop and refine, and won’t be cheap.

It’s still early days

If things are beginning to sound pessimistic, remember that only in recent years have satellites been planned and launched that demonstrate the potential for a space based carbon monitoring system. We have to learn to walk before we can run, and there is significant demand to develop the technology, infrastructure and ultimately an operational system.

The signing of the Paris Agreement has already catalysed increased action on the issue. Another international agreement, this one called the ‘New Delhi Declaration’, was signed by more than 60 of the world’s space agencies in May 2016. It acknowledges the need to evolve space-based tools, increase computing resources and develop new technologies and models to tackle the barriers and establish an international, independent system for estimating and curbing emissions based on accepted data.

There is, then, a combination of political will and scientific consensus to improve the way in which nations monitor their carbon emissions. The stakes are high, with the Paris Agreement calling for ‘a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century’. To put it simply, it aims for a world of net zero emissions in only a few decades, necessitating a rapid decrease in emissions.

The move to a more holistic system – where self-reported inventories are combined with increasingly accurate satellite observations and models – is an essential enabler for this ambition. Without it, the integrity of climate change targets could be drawn into question, undermining the hard-earned progress we’ve already seen.

Published: 06th Sep 2016 in AWE International