Greenhouse gases are essential for life on Earth. But too much of them cause Earth to heat up too much too fast, leading to climate change.
The climate change we are experiencing today is driven by human activities that increase greenhouse gas concentrations in Earth’s atmosphere. Although we mainly hear about greenhouse gases in the context of their contribution to climate change, they are in fact essential for life on Earth. Consider for a moment carbon dioxide’s (CO2) critical role in photosynthesis, and water vapour’s role in the formation of rain. Both of these gases are greenhouses gases. Greenhouse gases earn their name because they function much like the glass covering a greenhouse; they allow sunlight to easily pass through the atmosphere but trap the reflected heat energy so that it stays close to Earth’s surface. This greenhouse effect allows all the organisms on Earth, even us humans, to flourish. Without greenhouse gases, temperatures would drop, and our planet would be too cold to sustain life. However, high concentrations of greenhouse gases can also be harmful. Think for a moment of greenhouse gases as “blankets” covering the Earth’s surface: more “blankets” will trap more heat, giving rise to higher temperatures. This is exactly what is happening today—human activities are currently increased greenhouse gas concentrations in the atmosphere so much, and at such a fast pace, that Earth is heating up too fast for biodiversity to adapt to the changes.
Africa’s biggest contribution to climate change comes from the destruction of complex ecosystems, which leads to the loss of important carbon sinks.
At present, the single biggest cause of increased greenhouse gas concentrations is the burning of fossil fuels. Since the Industrial Revolution about 200–250 years ago, humans have become heavily dependent on the energy captured in these fuels—coal, oil, and natural gas—for activities such as transportation, heating, manufacturing, and electricity generation. Fossil fuels contain a high percentage of carbon, so when it is burned, that carbon is released into the atmosphere, generally as CO2. Consequently, since human populations started exploding and have been using fossil fuels at increased rates, the greenhouse effect has been significantly amplified.
While fossil fuel burning is currently the biggest overall driver of climate change, the greatest contribution from Africa is the destruction of carbon sinks, such as tropical forests (Box 6.1) and peatlands. Destroying these ecosystems contributes to rising atmospheric CO2 concentrations directly through burning of vegetation that releases carbon, and indirectly through the loss of vegetation that would otherwise extract CO2 from the atmosphere if they were still alive. The contribution of ecosystem loss to climate change is substantial: 13% of today’s global carbon emissions can be accounted for by tropical deforestation (IPCC, 2014). This impact is much stronger in Africa where deforestation accounts for 35% of the region’s overall climate change impacts (WRI, 2019). In comparison, Africa’s energy and agricultural sectors contribute 30% and 24%, respectively.
Box 6.1 Does Oil Palm Agriculture Threaten Biological Diversity in Equatorial Africa?
Abraham J. Miller-Rushing
Acadia National Park, US National Park Service,
Bar Harbor, ME, USA.
Oil palm (Elaeis guineensis, LC) is among the fastest expanding crops in the world. Native to West Africa, this species produces more oil per hectare than any other cultivated crop in the world. It should thus come as no surprise that it has become world’s most popular source of vegetable oil. Tropical Africa is poised as a hotspot for new oil palm plantations (Linder, 2013; Vijay et al., 2016). Is this a good thing? Will the benefits from jobs and carbon sequestration outweigh the loss of native ecosystems?
To many people, oil palm cultivation presents a win-win situation. The industry provides jobs and economic stimulus (Figure 6.A) and claims that oil palms sequester carbon from the atmosphere (Burton et al., 2017). This could potentially help countries offset carbon emissions; they may even receive funding from carbon markets. Palm oil can also be used for cheap bioenergy production, and as an ingredient in food and household products (e.g. cooking oil, baked goods, salad dressings, shampoo, and soap). Consequently, demand is rapidly growing as sales of processed and packaged foods (today about 50% of packaged foods include palm oil as an ingredient) expand globally.
Oil palm plantations, however, are rarely developed in environmentally friendly ways that allow them to realise their potential value. Rather, it generally comes at a great ecological cost. For example, to ensure net positive carbon sequestration, oil palm plantations must be developed on degraded landscapes, rather than displacing intact ecosystems that are already very effective at sequestering carbon (Burton et al., 2017). In practice however, intact forests are more often logged to make space (and additional revenue) for oil palm plantations (Ordway et al., 2019), resulting in habitat loss and net positive carbon emissions. Oil palm plantations are also often associated with great societal costs, like land grabbing, exploitation of local people, and displacement of traditional activities (Linder and Palkovitz, 2016). The influx of migrant plantation workers puts further strain on the environment through unsustainable hunting of bushmeat. One study found that primate population sizes declined by 25–100% after palm plantation development in Côte d’Ivoire (Gonedelé et al., 2012).
Recently, Herakles Farms/SG Sustainable Oils, an American agribusiness company, attempted to develop a 730 km2 oil palm plantation in Cameroon. This land grab would have been one of the largest palm oil projects in Africa, nestled deep within Cameroon’s lowland tropical forests, one of the continent’s most biologically diverse and threatened ecosystems. The forests threatened by this development is situated adjacent to four protected areas that include two national parks (Linder and Palkovitz, 2016), and host 14 species of threatened primates, including the Nigeria-Cameroon chimpanzee (Pan troglodytes ellioti, EN) (Linder, 2013). Residents and environmental groups opposed the plantation because of possibly illegal activities by the company, the ecological consequences of the project, and because the local people would have received little, if any, benefit from the project. After protracted debate and struggle, including intimidation and the arrest of local social and environmental activists, the company withdrew its Cameroonian plans in 2013.
It seems that there is potential for oil palm plantations to be good for economic development, job creation, and conservation. But in practice, companies establishing these plantations frequently exploit local people and degrade local ecosystems. They sometimes even do this under the auspices of sustainability, arguing that low-impact activities by traditional peoples indicate that the area is already degraded and thus suitable for development. Hopefully, one day we can live in a world where palm oil companies and robust legal systems truly consider the protection of biodiversity and the rights of local people in those operations.
The link between human-induced climate change and atmospheric CO2 concentrations was first highlighted in the late 19th century (Arrhenius, 1896). However, it was not until the mid-1950s (e.g. Kaempffert, 1956) that scientists started to raise concerns about increasing CO2 concentrations in the atmosphere. By the 1980s, as global annual mean temperatures started to rise, consensus about climate change linked to CO2 began to spread among the broader public. Yet concrete steps to curb CO2 emissions would only be initiated decades later (Section 12.2.1). In the meantime, CO2 emissions continue to accelerate (Figure 6.1): more than 37 billion tonnes of carbon, a new record, were released into the atmosphere in 2018 (Jackson et al., 2018; Le Quéré et al., 2018). To put it in another way, during 2018, humans released on average over 100 million tonnes of CO2 into the atmosphere every day.
The second-most important greenhouse gas that drives climate change is methane (CH4). Methane is a natural by-product emitted from decaying organic matter, most notably from wetlands that inhibit the speed of decomposition. These important ecosystem processes release methane into the atmosphere, albeit in relatively low concentrations. However, human activities have boosted methane emissions significantly over the past few centuries, through wasted food decaying at landfills, leaks from natural gas wells, an increase of industrial-scale cattle and dairy farms, and large-scale destruction of swamps and peatlands. Warmer temperatures also result in the drying of wetlands and peatlands; this drying speed up decomposition of organic material, which increases the rate of methane release. Methane currently constitutes 16% of all global greenhouse gas emissions released by humans (IPCC, 2014). This may not seem to be a major contribution; however, methane is 72 times more effective than CO2 in trapping radiation over a 20-year period (Forster et al., 2007), so even small increases in atmospheric methane can have dramatic effects.
The third important greenhouse gas that drives climate change is nitrous oxide (N2O), also known as laughing gas. Nitrous oxide is a by-product of synthetic fertilisers used in agriculture, burning of fossil fuels, and several industrial processes, and accounts for 6% of all human-caused greenhouse emissions (IPCC, 2014). However, it is even more potent than methane, and stays in the atmosphere for about 114 years, so the impact of one tonne of N2O is equivalent to 310 tonnes of CO2 over 100 years (Forster et al., 2007).