Africa’s Climate and How it Might Change
UNESCO, Nairobi, Kenya
Five key drivers of climatic conditions in Africa.
The science of climate change in Africa is too complex and fast-evolving to summarize in this guide. To effectively cover climate change, journalists should familiarise themselves with the regional drivers of climatic conditions and the ways that, within regions, topography, vegetation and the presence of large bodies of water can affect local weather.
North Atlantic Oscillation
• This term describes the annual variations of the westerly winds that cross the Atlantic Ocean from the Arctic. In years in which these winds are weaker, cold European winters can send fierce storms across the Mediterranean Sea, where they bring increased rainfall to North Africa.
Inter-Tropical Convergence Zone
• This is the equatorial zone where northeast and southeast winds close to the Earth’s surface merge, forming a band of clouds that give rise to tropical monsoons.
El Niño–Southern Oscillation
• For at least nine months roughly every five years, the Pacific Ocean experiences anomalously warm (El Niño) or cold (La Niña) temperatures. During La Niña, colder temperatures in the eastern Pacific cause low-lying winds to intensify, leading to wetter conditions over Southern Africa and drier conditions across equatorial East Africa from December to February.
• Every February, the storm system known as the West-African Monsoon migrates north from the equatorial Atlantic to the coast of Africa, making landfall along the western coast in June. Disrupting the normal dry, easterly winds of the Inter-Tropical Convergence Zone, the monsoon carries wet, southerly clouds across the Sahel during the summer, before moving south again in October.
Indian Ocean Dipole
• This describes the irregular warming and cooling of sea-surface temperatures of the western Indian Ocean. In its warmer phase, higher sea temperatures accelerate evaporation rates, and the resulting moist air carries increased rain to Mozambique and other parts of eastern and southern coastal Africa. Most of Africa experienced a temperature increase of roughly 0.7°C during the 20th century, and according to the World Meteorological Organization. The Intergovernmental Panel on Climate Change has said with “high confidence that it is virtually certain” that Africa will experience further warming across the majority of its major regions. To determine how climate change will manifest, scientists use mathematical models to make informed estimations. But with so many variables to consider, a lack of long-term data from much of Africa, and the obvious uncertainty of future human behaviour, much of what they know about the future of climate change is limited to generalisations. Generally speaking, though, two noticeable trends that have emerged in recent decades are projected to continue or even accelerate. First, the Sahel and southern Africa have become drier. Second, rainfall is projected to decline in the early phase of rainy seasons, but intensify in the latter portions. Indeed, since the 1970s, the North Atlantic has seen an increased intensity of its tropical cyclones, directly affecting the coastlines of North and West Africa.
Regional variations in climate
What follows is only an overview. For a more detailed information, journalists can consult the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.
• This region has arid and semi-arid climates, as well as tropical coastal areas. Already Africa’s warmest and driest region, it is only predicted to warm even further, a projection the IPCC calls very likely. With this increase in temperature will come a concurrent increase in the risk of heat stroke from May through October. When the North Atlantic Oscillation enters its weaker phase, storm activity across the region intensifies.
• The West-African monsoon system normally dominates the climate. Humid equatorial conditions give way to a rainy season from May through September. If climate change maintains its current pace throughout the next century, climate models predict wetter conditions in May (by up to 50 per cent in some areas) and late summer, either side of a mid-summer drought. These extremes could increase the likelihood of flooding. At the same time, experts expect the Sahel to see its hottest temperatures to date, with one model projecting a high risk of heat stroke for 160 days each year.
• Together, the migration of the Inter-Tropical Convergence Zone across the equator and the peaks and troughs of the El Niño–Southern Oscillation contribute to semi-annual rainfall cycle in Eastern Africa, marked by two periods of sustained rainfall: the ‘long rains’ from March through May, and the ‘short rains’ that peak between October and December, depending on the year. Climate variability is for the most part determined by Indian Ocean sea surface temperatures: in recent decades, a series of positive Indian Ocean Dipole phases have contributed to warmer ocean temperatures, which in turn have produced moist, easterly winds. As a result, there has been increased rainfall during the shorter rain season in the northern part of the region (the effect on the longer rain season remains unclear.) Farmers in East Africa, could reap the benefits of one of climate change’s silver linings in the years to come. This is because Indian Ocean temperatures are set to continue to rise. This could lengthen growing seasons in the highlands by increasing short season rainfall –anywhere between 8 and 22% across the region – and decreasing the severity of dry spells.
• Across Central Africa, climates range from tropical-dry to arid. Since the 1960s, the region warmed by 0.29°C per decade in tropical forests. Effects on precipitation vary within the region, with decreased rainfall in the Congo Basin, but a ten percent increase along Guinean coast. Scientists predict wetter June conditions particularly in the eastern part of the region, followed by severe drying in July and August.
Lake Chad: Where climate and mismanagement collide
Once 250,000 square kilometres in area, Lake Chad has shrunk to just one-tenth of its original volume, serving as one of the world’s most striking images of the physical consequences of climatic change. Experts blame much of the disappearance of the lake – upon which 30 million people in Niger, Chad, Cameroon, and Nigeria depend for their livelihoods – on both human actions such as inefficient damming and irrigation, and shifting climate patterns. But in 2007, UNEP and the Lake Chad Basin Commission concluded climate change is responsible for at least half of the shrinkage.
• With the exception of the extreme south-west of the region, which receives rainfall during the winter, southern Africa experiences a single, prolonged rainy season between the summer months of November and April. In the past 50 years, the total annual rainfall has not increased or decreased in a perceptible pattern, but the increasing variability of rainfall between years has put a stress on the region. Altered cyclone patterns in the southern Indian Ocean will carry more moisture to East Africa, and the majority of southern Africa (with localised exceptions throughout the region) is likely to become drier in the coming century, with rains decreasing by at roughly 10 per cent. In parts of Botswana and Namibia, average temperatures could rise by as much as 5°C.
Indonesian climate wields huge impact across the globe
4 April 2014