New but not normal
The year is 1822, and 54-year-old Joseph Fourier heads the French Academy of Sciences. Fourier had lived through the French Revolution and later served as scientific adviser to Napoleon Bonaparte. He was a brilliant mathematician and physicist whose work is still influential today.
Fourier was keenly interested in heat flow. He used the size of the Earth and its distance from the sun to calculate that our planet is far warmer than solar radiation alone should make it. Fourier speculated that atmospheric insulation could be the cause. This makes Fourier the first person to recognise what we now call the greenhouse effect.
The 1820s also saw the maturation of the First Industrial Revolution, which began around 1760. It was driven mainly by coal-fired steam power. The Second Industrial Revolution began around 1850 and included the growth of the petroleum and chemical industries and electrification.
The Irish-born John Tyndall confirmed the greenhouse effect experimentally in 1859. It was also the year that Svante Arrhenius — the first person to quantify the relationship between atmospheric carbon dioxide levels and global warming — was born. Arrhenius went on to become the first Swedish Nobel laureate.
Tyndall and Arrhenius studied the greenhouse effect because they were trying to understand past ice ages. By 1896, Arrhenius had concluded that carbon dioxide emissions from fossil-fuel burning would cause global warming. He thought this was good because it would prevent future ice ages.
Arrhenius’ optimism is understandable, considering that the world population was under 1.6 billion and atmospheric carbon dioxide levels had not yet risen much. But humanity was already heading for trouble.
Alarm bells start ringing
Even though scientists were warning of the risks of global warming by the late 1900s, it took until 1938 for data to show that land temperatures were rising. British engineer Guy Callendar demonstrated the increase and concluded that higher carbon dioxide levels were the cause.
Scientists argued about his results for another 20 years until atmospheric measurements began at Mauna Loa Observatory in Hawaii. It was initially directed by scientist Charles Keeling and has become the longest continuous carbon dioxide monitoring project. Keeling soon gathered data proving atmospheric carbon dioxide levels were rising.
Alarm bells started ringing as evidence of human-induced climate change mounted. A 1981 paper by climate scientists Tom Wigley and Phil Jones published in the prestigious journal Nature stated that the effects of carbon dioxide on climate may not be detectable until around the turn of the century. By then, atmospheric carbon dioxide levels would probably be so high that significant climate change would be unavoidable, so Wigley and Jones cautioned against waiting for unequivocal proof before taking actions such as reducing carbon dioxide emissions.
The first intergovernmental body reviewing greenhouse gases — the predecessor of the Intergovernmental Panel on Climate Change (IPCC) — was founded in 1986. The IPCC has published six reviews of climate science since 1990. The 2023 review synthesised more than 14 000 scientific papers into a nearly 4 000-page report.
The IPCC report confirms what Fourier and his successors suspected. The Earth’s atmosphere traps heat from the sun, just like a greenhouse. Gases such as carbon dioxide are called greenhouse gases because they increase this heat-trapping effect. Human activities have been emitting steadily more greenhouse gases since the Industrial Revolution, and we are now starting to suffer the consequences.
Average global temperatures have already risen 1.1 °C. Warming will probably exceed 1.5 °C this century, and keeping it below 2.0 °C will be challenging. But humanity has to rise to this challenge, or our planet may cease to be habitable — at least for our species.
The Western Cape perspective
The Western Cape Department of Agriculture recently commissioned a report on climate change trends and projections for the province. The study was led by climate scientist Dr Chris Jack of the Climate Systems Analysis Group at the University of Cape Town. It looked at the entire province, but only results for fruit-growing areas will be included below.
Trend analysis shows that temperatures have increased by about 0.1 °C per decade throughout the province. Daily maximum temperatures have increased slightly more in inland areas, and daily minimum temperatures have increased slightly more in coastal areas — see figure 1.
Higher temperatures have resulted in higher evaporation rates. These trends are strongest in the most southern and western areas. Increases in evaporation rates are also greater in spring and summer.
Rainfall trends are less clear. The strongest trends for rainfall reduction are for autumn, and interior regions such as the Bokkeveld are more affected. Strong drying in winter was only seen for the Bokkeveld.
Jack reported that temperatures are projected to increase across the Western Cape. Mean temperatures averaged for the province will probably increase by 1.0–1.8 °C by 2060 compared to 1981–2010. The number of days exceeding 30 °C will likewise increase.
Evapotranspiration rates are projected to increase across the province. Rainfall projections vary between models — some project minimal reductions, whereas others project up to 20% reduction in annual rainfall — and by region. Droughts are likely to become more frequent and severe.
A 2021 Hortgro-funded project assessed climate change impacts on pome- and stone-fruit production. It was led by Prof. Stephanie Midgley, Specialist Scientist for Climate Change at the Western Cape Department of Agriculture.
Midgley and her team developed a guide to climate change that includes maps of projected temperatures, evapotranspiration, and chill-unit accumulation. They also considered sunburn risk and red colour development. Their focus was the likely change by the 2030s and 2050s.
The main findings were that reduced winter chill makes pome-fruit production in the EGVV more challenging, while high-temperature risks would impact inland areas such as the Bokkeveld, Wolseley, and the Langkloof. All pome-fruit production areas would have fewer days conducive to red colour development.
Stone-fruit production would become more marginal in warmer areas such as parts of the Klein Karoo. Higher evapotranspiration rates will increase the irrigation demand in all fruit-production areas.
Adapt and thrive
The details might differ, but the headline conclusion is that pome- and stone-fruit growers must adapt to higher temperatures and greater water demands. Some growers will also have to cope with extreme weather events, including droughts or floods. But everyone will have to make changes regardless of the specifics of their site — the world demands it.
Under the global Paris Agreement, South Africa has committed to carbon neutrality by 2050. Although our emissions have plateaued since 2010, we still have a long way to go. Our new Climate Change Bill is a good start — it should be enacted within the next few months.
The Climate Change Bill aims to regulate climate change mitigation, manage climate change adaptation, and assign mandates to various government departments. It sets targets and measurement and reporting requirements for different sectors. The implications for agriculture will become clearer once the bill is enacted.
In some respects, South African growers are already primed for new legislation due to demands for sustainable production from our markets. And these are likely to increase under programmes such as the European Green Deal.
It may seem that our industry is drowning in regulatory and reporting requirements, from tracking carbon footprints to juggling chemical residues. Meanwhile, production costs continue rising and profits shrinking. What does this mean for the long-term survival of pome- and stone-fruit growers?
Adapting to a world of 8.1 billion people competing for limited water and energy is how our industry will thrive. The 2015–2018 drought taught us better water management, while the latest round of load-shedding pushes us to improve energy efficiency. Market pressures drive innovation in crop production and protection, ultimately translating into greater cost-effectiveness.
The rise of regenerative agriculture is an example of the co-benefits that come with climate-friendly practices. Building soil carbon keeps carbon out of the atmosphere while improving soil water-holding capacity. On top of that it promotes soil fertility and may reduce the need for fertilisers and spray applications.
Other countries are investigating innovations such as solar panels for shading orchards and powering electric orchard vehicles — these vehicles could even be autonomous.
The evidence for a warming world is unassailable. Even if emissions stopped today, we already have elevated atmospheric greenhouse gas levels that will continue to trap heat. Adaptation will mean recreating our civilisation — and South African pome- and stone-fruit production — in ways the pioneers of the First Industrial Revolution could never have imagined.