20 years of trend maps reveal a surprising picture of climate change on Kilimanjaro

Mount Kilimanjaro is warming in some places and cooling in others, according to a new study by the University of Portsmouth, published in npj Climate and Atmospheric Science.  

Analysing temperature records collected over 20 years ranging from 900m to 5803m above sea-level, researchers found that daytime temperatures near the summit rose strongly, while the strongest cooling occurred on the middle slopes, between 3,000 and 3,500 metres above sea level.  

Long-term temperature records covering such a large elevation range are particularly rare in tropical mountains, where weather stations are often sparse, especially at high elevations. The researchers describe Kilimanjaro as the best-monitored tropical high-elevation mountain in Africa, with temperature sensors installed and maintained by the University of Portsmouth spanning around 5,000 metres of elevation.  

Kilimanjaro provides a unique open-air laboratory because it rises from the East African plains to almost 5,900 metres, creating a series of distinct environments as you move upslope, including cultivated land, tropical rainforest, heathland and alpine desert, before reaching its ice-covered summit. This range of habitats allows researchers to investigate how temperature trends vary with elevation and local environmental conditions.  

Professor Nick Pepin, from the Institute of the Earth and Environment at the University of Portsmouth, said: “Climate change does not affect every part of a mountain in the same way. Long-term observations across different elevations help us see these local differences and build a more accurate picture of how mountain environments are changing.”  

The researchers combined measurements from 22 temperature loggers operating across Kilimanjaro from 2004 to 2024 with satellite observations and other environmental data. This enabled them to estimate air temperatures across the whole mountain at a resolution of one kilometre, rather than relying only on readings from individual monitoring stations. The approach provides a detailed picture of how temperatures vary across the mountain and between daytime and nighttime.  

The combined data showed that daytime temperatures near the summit rose by between 0.05°C and 0.10°C per decade during the period analysed, while temperatures between 3,000 and 3,500 metres fell by approximately 0.13°C to 0.14°C per decade. At night, most elevations experienced slight warming, while summit temperatures remained broadly stable. 

University of Portsmouth PhD student Yaping Mo, the study’s lead author, explained: "The cooling on the middle slopes coincides with the upslope expansion of the heathland zone. This signals that changes in vegetation and land cover may be influencing local temperatures, although other factors are also likely to contribute.  

"Further down the mountain, the rainforest zone has showed relatively little daytime warming. This indicates that conservation and reforestation efforts may have helped limit local temperature increases, although this relationship requires further investigation."  

Vegetation affects how much sunlight reaches the ground and how heat moves between the land and the air. More healthy vegetation can divert the sun’s energy away from heating the air and keep conditions cool.  

The study also highlights a challenge in researching mountain climates using satellites. Satellite measurements record the temperature of the land surface, which can be very different from the air temperature. During the dry season, exposed ground can be 10–15°C hotter than the surrounding air. However, the researchers developed a model to be able to predict one from the other, thus enabling the full potential of the satellite data to be realised in mapping temperature changes across the whole mountain. 

Dr Harold Lovell, from the School of the Environment and Life Sciences at the University of Portsmouth said: “Our research shows that warming is not necessarily uniform across a mountain, even over relatively short distances. Combining long-term ground measurements with satellite data helps us identify these differences and could provide a way to study temperature changes in other mountainous regions where weather stations are limited.”  

Expansion of this approach to other regions could help scientists build a more detailed picture of how mountain climates are changing and improve understanding of how local landscapes influence temperature trends.