"The transition to a low carbon economy is unstoppable." That was just one of a myriad of commentators welcoming the agreement reached at COP21 by the world's governments. The rise in global temperature caused by greenhouse gases is to be kept "well below" 2 °C (with further “efforts” to limit it to 1.5 °C) and progress of the countries' Intended Nationally Determined Contributions (INDCs) are to be reviewed every five years. These INDCs are each country's emissions reduction pledge, achievable only through a concerted effort to measure and mitigate emissions by all who produce greenhouse gases. The agreement also sets out a “facilitative dialogue” in 2018 to take stock of the collective efforts of countries and to inform future commitments. Given the failure to come to agreements in Copenhagen in 2009, it is no surprise this agreement is being met with such positivity.

In order to ensure the successes of the conference continue, the next step must be to determine how exactly these emissions targets are to be measured. Numerous climate think tanks have been quick to point to data that implies even if the INDCs were met, warming would be halted at around 2.7 °C. There is no consensus on what the data forming the foundation of nearly 200 INDCs means, and because INDCs are the responsibility of the individual country, each will be collecting data in a different way.

Currently the agreement seeks to establish an “enhanced transparency framework” to keep track of progress but it also includes a “built-in flexibility” to try and cover the range of national capacities to implement this. Agreeing a global standardised system of measurement, reporting and verification is the only way to see the INDCs fulfilled, and understand their impact so that they can be reviewed properly. This issue was also highlighted during the negotiations, with Bill Clinton's former scientific adviser stating "if we don't have strong verification and monitoring, we don't have a strong agreement."
As well as agreeing a standardised system of emissions measurement, we also need to ensure that this system is robust, and that we can be sure that the INDCs pledged by each country are having the desired impact.

Standard models of emissions measurement currently use a bottom-up approach, which estimates emissions based on activity data (for example, electricity consumption in kWhs) multiplied by an "emission conversion factor" (for example, the amount of carbon dioxide attributed to the use of one kWh of electricity). In other words, it calculates the amount of greenhouse gas emitted based on activity performed. These factors are established using direct measurements, but some countries do not have the means to make these measurements and hence rely on unsuitable data from elsewhere. Emissions from some sectors, for example electricity, are very country specific due to the different energy mixes; in agriculture uncertainties in emissions from livestock or fertilizer use can be greater than 50%. We need to improve on this if we are to ensure the INDCs are met and we also need to provide support for developing countries to make their own measurements that are applicable to their particular circumstances.

There are various emissions measurement methods that all come with a range of sophistication, accuracy levels and costs.

A system on the more sophisticated end of the range is the Differential Absorption LIDAR (DIAL), a mobile facility able to monitor atmospheric pollutants remotely at ranges of up to 3km. Concentration and spatial distribution of atmospheric pollutants can be determined directly, producing 3D concentration profiles in real-time situations where emissions need to be pinpointed and quantified. It measures upwind and downwind to differentiate between emissions which could be blown onto the site from other sources and covers a wide range of gases and volatile organic compounds that cause anthropogenic climate change.

A less sophisticated, but lower cost, option is a portable remote infrared imaging system. These are popular for leak detection within the gas industry as they can be used systematically to check individual valves and other common sources. It cannot quantify the volume of the leak, but it can establish the source.

Other systems fill this gap by measuring the amount of emission present in the air, such as Cavity Ring-down Spectroscopy (CRDS) which measures continuous ambient emission concentrations with very high accuracy.

A mixture of such methods is the best way to ensure appropriate direct measurements are done. These can provide the required certainty levels when reporting on emissions, achieving accurate assessments and comparisons.

These ground-based methods can also be partnered by climate monitoring from satellites, giving an accurate, global view of greenhouse gas levels. For example, the US satellite OCO2 measures carbon dioxide from space, and European organisations have plans for a similar satellite called CarbonSat which would also measure methane emissions. The introduction of a system that can calibrate the data provided by these satellites to ensure trustworthy data is something the National Physical Laboratory is working on through the TRUTHS mission.

The technology is available to facilitate the clear and transparent monitoring of INDCs aimed at limiting our climate impact and now it seems the political will is too. What must follow is an agreed, unambiguous method for assessing greenhouse emissions within and across all countries. Without this there will always be room for disagreement and mis-reporting, something that our climate can ill afford.



Marieke Beckmann, Research Lead, National Physical Laboratory Centre for Carbon Measurement, United Kingdom.
The Centre for Carbon Measurement reduces uncertainties in climate data, provides the robust measurement that is required to account for, price and trade carbon emissions and helps develop and accelerate the take up of low carbon technologies.

Image: New York City's daily carbon dioxide emissions as one-tonne spheres. By
Carbon Visuals. CC-BY license.