Working backward, a way to find out where the carbon came from

Based on carbon dioxide concentrations at a location and wind speed, scientists trace particles back to their sources to identify whether the country is an emitter or a carbon sink, say Eurasian region is a net carbon sink.

Written by N K Indira , P S Swathi | Csir Fourth Paradigm Institute Bengaluru | Published:July 24, 2017 5:51 am
climate change, carbon footprint, co2, carbon origins, atmosphere, paris agreement, indian express Based on carbon dioxide concentrations at a location and wind speed, scientists trace particles back to their sources to identify whether the country is an emitter or a carbon sink, say Eurasian region is a net carbon sink

As part of the global fight against climate change, all countries are making efforts to reduce emissions of greenhouse gases like carbon dioxide. There are two ways of bringing down the levels of net emissions. One way is to reduce the actual emissions. The other way is to increase tree and forest cover that absorbs carbon dioxide thereby taking it out of the atmosphere. Trees and forest cover, therefore, act like a carbon sink. In addition, oceanic ecosystems also fix atmospheric carbon.

As part of the 2015 Paris Agreement in climate change, every country, including India, has submitted what is known as nationally determined contributions (NDC). These are a set of actions that countries have promised to take as their contribution to the fight against climate change. Countries have to report to the international community from time to time to show progress on their promises.

In its NDC, apart from some other things, India has promised to create an additional carbon sink that will absorb between 2.5 to 3 billion tonnes of carbon dioxide every year. Creating new forests and improving the quality of existing forests in order to create that large a carbon sink is a herculean task.

Key to the fulfilment of these promises by India is its ability to measure its emissions and absorptions of carbon dioxide with a great amount of accuracy and through internationally standardised procedures. The problem is that once carbon dioxide is emitted into the atmosphere, it does not remain within the confines of national boundaries. It spreads quickly and within a year mixes up uniformly in the atmosphere over the entire earth. It is not possible to identify the source of the increase in carbon dioxide by simple procedures.

Measurements, therefore, are a complicated exercise. WMO (World Meteorological Organisation) demands an absolute accuracy of 0.1 parts per million of carbon dioxide and 1 part per billion of methane in order to discriminate between minute signals in the secular increase of these species. This level of accuracy is achievable only by careful calibration traceable to primary standards. Attempts to make these measurements in India are fairly recent. We now have four stations from which we take continuous measurements. The first one was set up in Hanle, in Ladakh, in 2005 and subsequently such stations also came up in Puducherry, Port Blair, and Hoskote near Bengaluru.

There are different ways to assess whether a country is a net emitter of carbon dioxide or a net sink. To assess the size of the carbon sink, for example, one can carefully monitor the year-by-year increase in forest and vegetation cover through satellite imagery and other methods. By knowing the absorptive capacities of different kinds of vegetation and their annual variations, one can calculate the increase or decrease in the size of the carbon sink. Another way is to measure biospheric carbon fluxes representative of typical vegetation with flux towers and scale them up to country aggregates. However, heterogeneity of vegetation and their spatial extent make this a difficult exercise. Oceanic fluxes are a problem due to accessibility and lack of data.

So what we do is a bit of backward analysis. We measure the concentrations of carbon dioxide at a particular location and then trace the particles back to their sources, using information like wind speed and direction, to assess whether the source was located within the country or was outside. There are fairly robust and statistically sound methods for doing this.

Though we need many more stations across the country — we do not have a single continuous monitoring station in western India — to improve the accuracy of our estimates of sources and sinks, we have been carrying out continuous measurements at the four locations and studying the data that is being generated. Using the data from Hanle, and those generated in other countries from similar stations, we have recently been able to show that the temperate Eurasian region, which includes India, was actually a net carbon sink. It means that more carbon dioxide was being absorbed by the forest cover in this region than was being released into the atmosphere through the emissions. The net sink was worth about 5.5 billion tonnes of carbon dioxide every year (equivalent to 1.5 billion tonnes of carbon).

More monitoring stations would help us to make similar assessments about India as well. It is only through these kind of precise measurements that India can claim to have delivered on its promises. Besides, this will also allow us to monitor the compliance of other countries in fulfilling their NDCs.

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