A landmark new study has found that, in the last decade, the African continent has started emitting more carbon than it stores. When the total amount of carbon that is sequestered by natural ecosystems (such as the soil and plants in grasslands, savannas and forests) exceeds the amount of total carbon emissions within a system, it’s referred to as a net sink of carbon. But, the study found, as natural ecosystems are converted for agricultural purposes, the carbon storage capacity is decreasing – while the rate of emissions is increasing.
Yolandi Ernst of the University of the Witwatersrand (Wits) in South Africa led the international research team that calculated the flows of carbon dioxide, methane and nitrous oxide through Africa’s terrestrial and aquatic ecosystems. She and one of the study co-authors, Sally Archibald – also from Wits and the lead of the Future Ecosystems for Africa Programme – unpacked their findings for The Conversation Africa.
What did you set out to calculate, how did you do it, and why?
We wanted to know both the amount of greenhouse gases being produced by the African continent and the amount being taken up. This helped us to develop a greenhouse gas budget, quantifying the net amount of outgoing and incoming greenhouse gases. In this way we’re better able to understand how the continent is contributing to global climate change (by releasing greenhouse gases) and how, through taking up greenhouse gases, it’s helping to mitigate global climate change.
This study formed part of a global effort by the Regional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project. It aims to establish improved greenhouse gas budgets for large regions covering the entire globe at the scale of continents (or large countries) and large ocean basins.
We collated data from a variety of sources and created models to calculate the amount of carbon dioxide, methane and nitrous oxide (collectively called greenhouse gases) being released into the atmosphere from several different sources. Some are human sources, like agriculture and fossil fuel emissions. Other sources, like wildfires and termites, are natural.
Then we calculated the amount of carbon that’s drawn down from the atmosphere and stored in what are called carbon sinks: the soils and plants in grassland, savanna and forest ecosystems.
The net budget estimate was the result of adding all the sources and sinks, just like balancing a household budget, where you don’t want to be spending more than you are earning.
This information is crucial for policy making. If scientists, land managers and NGOs know which activities produce the most greenhouse gases they can work with governments and policymakers to minimise this. And knowing which parts of Africa best help to store carbon means funding and policy efforts can be directed to protecting and increasing this carbon “land sink”.
What are the biggest sources of carbon emissions on the African continent?
It’s important to distinguish between anthropogenic and natural emissions here. Fossil fuel burning and agriculture are the biggest sources of carbon emissions; both are anthropogenic (caused by humans). Other emissions are part of the ecosystem functioning but they can also be affected by human activities. Examples include fire, methane emissions from herbivores, and inland and coastal water bodies. These all represent quite large emissions, but they’re only somewhat affected by human activities.
In Africa’s case, our budget shows that when people transform natural landscapes for agricultural and other purposes, the emissions from fire decrease, but emissions from herbivores increase.
There are also some important natural processes that draw carbon and greenhouse gases back into the land surface. These include the growth of vegetation and soil carbon storage, as well as weathering of rocks (which turns atmospheric CO₂ into carbonate minerals), and burial of carbon in the ocean.
The previous African carbon budget (1985-2009) showed the processes drawing carbon into Africa were higher than the natural emissions and the anthropogenic emissions. The continent was a carbon sink even though it emitted some anthropogenic greenhouse gases: Africa was providing a climate service to the globe.
Globally the anthropogenic emissions of CO₂ are 11.21 gigatons of carbon per year (GtC/yr), but the land takes up about 3.5 GtC/year, so it is helping to slow the growth rate. The African land sink is about 0.8 GtC, representing about 20% of the world’s total land sink.
Now, although the sink capacity hasn’t decreased – Africa is still taking up just as many greenhouse gases as it did in the past – the amount of anthropogenic sources has increased so much that the net effect is to be releasing greenhouse gases. In short, the continent has become as much of a carbon source as it is a carbon sink over the study period (2010-2019).
What can be done to reverse the trend you’ve identified?
Finding ways for Africa to develop in a way that is carbon neutral is a big challenge. Investment in carbon-neutral energy sources and reducing reliance on fossil fuels would be a start.
But this has never been done – all developed countries have grown their economies on the back of massive fossil fuel use. If African countries are to become carbon-neutral and also grow their economies, global support and funding will be required.
However, fossil fuels are only part of the problem in Africa as less than half the continent’s greenhouse gases currently come from fossil fuels; land use change and agricultural expansion are the leading cause of its emissions. There are many innovative approaches to producing food in ways that emit fewer greenhouse gases – again, the challenge is to find ways to roll these out at scale
Protecting, managing and restoring the landscapes that are helping to take up the excess carbon dioxide can also help a lot. But there are challenges here, too. Making carbon storage the main goal of conservation can conflict with biodiversity and water provision.
Mixed cattle-wildlife systems and novel livestock management methods show promise for reducing climate impacts and improving landscape functioning.