Area of rice harvested in Africa. The top panel shows growth in rice area for 2000-2018. The black dotted line designates 2008, the year the first phase of the CARD program began. Growth rates of rice area in SSA are shown, including the 23 CARD member countries as shaded on the inset map. The bottom panel shows the growth in rice area between 2008 and 2018 for each of the 23 CARD countries and for the rest of Africa (others). FAOSTAT data32. Credit: Climate change (2024). DOI: 10.1038/s41558-023-01907-x
A team of engineers and atmospheric scientists from Harvard University, working with a colleague from the Jet Propulsion Laboratory at the California Institute of Technology, calculated the increased amount of methane expelled into the atmosphere due to the increase in rice cultivation in certain regions of Africa.
In their article published in the journal Natural climate change, The group describes how they recalculated methane emissions from recent increases in rice production in sub-Saharan Africa, and what they discovered in doing so.
Previous research has shown that methane is the second most important greenhouse gas (behind carbon dioxide): it has more radiative properties (it retains heat better) than CO.2which means that even if it is released into the atmosphere in much smaller quantities, it still plays a major role in global warming.
Previous research has shown that agricultural activities (crops and livestock combined) account for about 25% of all human-caused methane emissions into the atmosphere. Waste disposal and fossil fuel production account for most of the rest.
Previous research has also shown that rice production in sub-Saharan Africa doubled between 2008 and 2018 – a good trend for feeding people (it currently accounts for around 9% of the continent’s calorie intake) but not so good for environment. Rice cultivation releases very large amounts of methane into the atmosphere.
In this new effort, the researchers started with figures representing Africa’s total greenhouse gas emissions before 2008, then added the amount emitted due to factors involved in growing rice, such as irrigation, flooding of cakes, burning of fields and harvest.
As part of this effort, they assessed the extent of rice cultivation, including more precisely delineating rice-growing land and the number of days that rice fields in Africa emit methane. They then used what they learned to calculate new estimates of atmospheric methane emissions for all of Africa.
The research team found that increased rice production in Africa accounted for about 31% of the increase in methane emissions for Africa as a whole between 2006 and 2017, and 7% of the increase global methane emissions for the same period.
More information:
Zichong Chen et al, Rice cultivation in Africa linked to the increase in methane, Climate change (2024). DOI: 10.1038/s41558-023-01907-x
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