The world's poorest communities have begun to experience extreme weather outside the natural variability of African climate. Without a rapid reduction in emissions, the continent faces calamitous temperature rises within this century

We are right on the equator, and Speke, Moebius, Elena, Savoia and Moore, the five great glaciers of the the Rwenzori, the Mountains of the Moon, glint in the bright Ugandan sun. Usually lost in the mists that cloak these peaks up to 5,100 metres high, the glaciers are the only major ones left of the 43 that were mapped and named in 1906. Then, the ice covered 7.5 square kilometres, now it is thought to cover less than one.

Surveys suggest most of the glaciers shrank by nearly half between 1987 and 2003. They will be measured again in January, but air temperatures in all the high tropics have risen several degrees in a few generations and, says the British hydrologist Richard Taylor of University College London, it's likely that the equatorial ice known to the ancient Greeks will almost certainly have disappeared in 20-30 years.

The Rwenzori glaciers cannot be saved by the 194 countries meeting in the UN climate talks in Durban, South Africa, which will move up a gear this weekend as ministers and some heads of state arrive for the serious negotiations.

But if the rise in greenhouse gas emissions is not stopped and then rapidly reduced within a few years then Africa, the most vulnerable and poorest continent, will almost certainly experience 4-5C temperature rises within a century, according to the consensus of world climate scientists. Comparatively little research has been done into the possible impacts of climate change in Africa and there are deep uncertainties about timing and severity in individual countries, but the scientific consensus – from the Intergovernmental Panel on Climate Change – is that a rise in temperatures of just 2C would guarantee more intense droughts, heatwaves, floods, stronger storms, sea level rises, crop losses and unliveable cities, and a rise of 4-5C would be calamitous across much of the continent.

From Cairo to the Cape, the impact of man-made climate change is already being felt. Farmers, people in cities, local scientists and governments all tell a remarkably similar story – that there is evidence of more extreme and unseasonal weather taking place outside the natural variability and cycles of African climate, and that the poorest communities are the least able to adapt.

In Egypt's Nile delta, where 40% of the population lives, most of the land is liable to be inundated by a one-metre increase in sea levels, anticipated over the next century. Guy Jobbins, a Cairo-based British water scientist who heads Canada's International Development Research Centre climate change adaptation programme for Africa, says understanding of the issue has rocketed in the past few years.

"Go to any farm, talk to any fisherman, and climate change fits their experience. The last few years have seen temperature spikes to world-record highs. We don't absolutely know it's climate change but we do know that the summers are hotter now, and the impact of evaporation is greater in the south of Egypt. We see crops dying in the fields, temperatures of 63C [145F] have been recorded, and the winters are not cold enough to grow olives. There are some advantages, like the fact that vegetables grow earlier, but smallholders have no way of taking advantage.

"We know sea level rise is happening but it's slow and steady. But the effect is being aggravated by the increasing intensity of storms. Last year saw the worst [storms] in decades. The last few years have seen temperature spikes, with nights becoming unbearably hot and then switching to freezing cold. But the real issues are groundwater and soil salination. Coastal aquifers become depleted, which leads to groundwater becoming salinated. As sea levels rise the water becomes more stagnant and salty. It's affecting hundreds of square kilometres, up to 10km from the coast in places. … Climate change is a massive problem for developing countries because people are less resistant to shocks and cannot adapt."

A thousand miles south in Khartoum, Sumaya Zakieldeen, a researcher at Khartoum University's institute of environmental studies, says the harsh climate that Sudan already experiences will become more extreme. She and her team have compared historical data going back to 1940 and found drought and extreme flooding more frequent, temperatures rising in winter, extreme – good and bad – years now more common and rainfall patterns changing.

A major UN study from 2007 – From Conflict to Peacebuilding: The Role of Natural Resources and the Environment – says temperatures are set to rise by several degrees in the next 50 years, with rainfall declining 5%. Climate change, say the authors, presents a "new and harsh reality".

To the east of Sudan, the Horn of Africa is experiencing its worst drought in 60 years. Somalia, parts of Ethiopia and Kenya, and a great swath of Africa stretching to Chad, have always experienced severe droughts and scorching temperatures. But this is different, says Leina Mpoke, a vet in Moyale on the Kenya-Ethiopia border.

"In the past we used to have regular 10-year climatic cycles which were always followed by a major drought. In the 1970s we started having droughts every seven years; in the 1980s they came about every five years and in the 1990s we were getting droughts and dry spells almost every two or three years. Since 2000 we have had three major droughts and several dry spells. Now they are coming almost every year, right across the country."

He reels off the signs of climate change that he and others have observed, all of which are confirmed by the Kenyan meteorological office and local governments. "The frequency of heatwaves is increasing. Temperatures are generally more extreme, water is evaporating faster, and the wells are drying. Larger areas are being affected by droughts, and flooding is now more serious."

'It is no coincidence that the worst affected areas are those suffering from entrenched poverty. Severe drought has led to the huge scale of the disaster, [but] this crisis has been caused by people and policies, as much as by weather patterns. One thing is clear. If nothing is done, climate change will in future make a bad situation," says Tracy Carty, Oxfam policy adviser.

Further south, on the Tanzania border, the semi-nomadic Maasai, who never used to cultivate food, have been hit repeatedly by droughts, which have forced them to adapt by herding cattle less and growing beans, fruit and vegetables.

"These days the water evaporates faster and the grass dries very quickly. Last March it rained, but very little. So now I try to cultivate. We have greatly changed our life but so far not much is going better," says Simatoi Tirike, one of a group of around 1,300 in the Maasailand division of Magadi.

Most of his community have only a few cows left. "It's definitely hotter now. We had many cows, but now we have few and they get sick more quickly. The rivers used to flow all the year but now not so much. The winds are stronger and we have new livestock diseases. I used to be able to work many hours in the fields, now just a few hours. Sometimes it rains for two or three weeks now but then it stops. Very long droughts now affect the cattle."

A spokesman for the Kenyan environment ministry says: "We are vastly endangered by climate change. The minimum temperature has risen generally 0.7-2C and the maximum 0.2-1.2C. There is generally less rain. More intense rainfall occurs, and more frequently. This means the frequent occurrence of severe floods.

"We have had the mass deaths of animals, famine, a great influx of refugees from Somalia and armed conflicts over water. It means we have to look for aid. Adaptation is now our priority. Climate change is now central to our planning."

The minister for environment and natural resources, John Michuki, says: "If the world does not implement measures that result in deep cuts in anthropogenic emissions, such impacts will only worsen in future."

Back on the equator, the coffee farmers of Rwenzori expect to grow only 5,000-6,000 tonnes of beans, compared with 15,000 tonnes 10 years ago. It's largely because temperatures have risen dramatically, and the arabica coffee that they have always grown needs quite specific temperatures.

Coffee growing is now far less profitable below 360 metres. "I can't produce anything like I used to. The temperature goes up all the time. I used to harvest nearly three times as much coffee. This year there's been lots of rain but that is unusual. Everyone is in the same situation. We have new diseases. It affects all crops," says Fidel Nzeomasi, a small farmer.

Changing rainfall in the Rwenzori hills has resulted in less water to power three hydroelectric plants. Nearly 75% of all Kenya's electricity is generated by water and whenever the rains fail there is a dramatic drop in water levels at many of the reservoirs. "The effect on Kenya's export industries is catastrophic as much of the country's exports are based on fresh produce, and a lack of reliable power creates havoc with irrigation and temperature controls in greenhouses," says Steve Mutiso, Oxfam's disaster risk reduction officer. "Any drought in Rwanda, Uganda, Kenya or Tanzania can knock off power."

One thousand miles further south in Zimbabwe, there is a large-scale community response to climate change in Gutu district, Masvingo province. Rain-fed farming has become nearly impossible because of constant droughts, and irrigation provides 25,000 households with some certainty.

"Our land was fertile and we used to get good harvests but then the weather changed, the rain is really erratic. You work and work but get nothing back if there's no water. We just dream of rainfall. The weather has changed, the climate has changed. There are no signs telling us whether rains will come or not. There are so many dry spells we cannot even grow enough to survive for the whole year. But with our irrigation scheme we can survive all the way through to next year now," says Ipaishe Masvingise, a 46-year-old widow.

South Africa's emissions of more than nine tonnes per person of carbon dioxide a year is more than four times that of any other African country and greater than that of France or Britain. But the vast majority of the power is used by the mining, power and aluminium industries, which mainly work for export. More than 2.5m homes have no electricity at all and 70% of rural households still rely on wood fuel.

But climate change and the need to mitigate emissions is helping to break the old monopoly of coal power. There are plans to rapidly expand wind power in the Western Cape near St Helena's Bay, where winds blow constantly off the Atlantic. Neil Townsend, director of Just Energy, a start-up company, hopes to build four small farms, which would have 40% community ownership.

"Investors are queueing up. This could be a model for community windfarms around the world. We reckon just 10 3MW turbines here can provide an income of around £20m over 20 years. If the four farms are given licences they could together provide education, job opportunities and business loans for nearly 20,000 of the poorest people in South Africa. Climate change is creating the opportunity for these projects," says Townsend.

One place that should benefit is the Laingville township near Saldanha Bay, where there is 90% unemployment. "This project would make a significant difference to the whole area," says Johan Akron, spokesman for a group of 200 relatively poor local people who bought the farm as part of a land redistribution project. "Fishing here has declined. There's nothing else."

Climate change could possibly benefit farming in southern Africa because extra carbon dioxide in the air from fossil fuel burning could promote plant growth, but mostly it threatens water supplies, farming, wildlife and health, say scientists and the government.

A new report by the South African government expects the geographic range of malaria to nearly double in the next 50 years, and rainfall to decrease by around 10%. It predicts that by mid-century, 50 million to 100 million extra people in southern Africa countries will experience water shortages. Weather patterns are changing and "hotspots" such as Botswana can expect temperature rises of 5C by the end of the century, which could make any life there nearly untenable.

But how far climate change is already affecting natural ecosystems is hard to tell, says Guy Midgley, head of the South African national biodiversity institute in Cape Town. "Climate change could mean unthinkable loss for South Africa. But there are large gaps in our knowledge and we need more research. What we do know is that millions of people's lives are at stake. The well-being and lives of vulnerable populations are on the frontline. A very significant change is happening very rapidly and it's outside our evolutionary history. This is an evolutionary sledgehammer."

• Travel and accommodation was supported by Oxfam, and the African Investigative Journalism Conference at Wits University. Neither organisation had any control over content of the article.