As stated previously, the climate goes through different cycles of variable duration, alternating between cold and hot periods. Historical evidences of long-term changes in the climate of Nigeria are scanty. However, we can use proxy data from regional sources for Africa in general and the Lake Chad in particular to provide some evidence of long-term past changes in the climate of the country. It may be difficult for many to believe, but evidences point to the fact that Africa has gone through different climate periods in the past.
About 20,000 years ago, the continent was almost a desert, but a rainy period ensued between 7,000 and 14,000 years ago. It lead to the eradication of most arid areas and enabled the development of agriculture and cattle breeding in the present day Western Sahara. The existence of a gigantic Lake Chad, which covered over 340,000 km2 (the size of Côte d’Ivoire today) and with a maximum depth of 160m, about 6,000 years ago attests to these historical fluctuations. This implies that much of the current dry region of the northeastern part of Nigeria was very wet about 6000 years ago.
The climate in Africa today is almost the same as 2,000 years ago, with more arid or more humid phases. The era between the 10th and 15th centuries was a rainy period during which living conditions were far more favourable than they are today. However, since the early 19th century, the continent has been struck by an arid period that lasted a few decades, which continued till the 20th century. Today, most of the African continent is tropical, except for the Mediterranean region and South Africa.
The history of the Lake Chad variability can be used to provide useful information of past climate changes in Nigeria, at least for the northern part of the country. There are evidences to indicate that the Lake completely disappeared several times in the past. The Lake Chad actually dried out around year 1450, 1550, 1750, 1850 and 1900, all of which will indicate extremely dry conditions for the northern part of Nigeria in these periods. Hence, recent concerns about the Lake Chad Region must be put in its historical perspectives.
Concerning recent trends, instrumental records show evidences of marked variability in the recent mean temperature and rainfall conditions in Nigeria. Over the last six decades, there has been a general increase in temperature throughout the country, particularly since the 1980s. The warming revealed a change of 1.01°C in the mean conditions for the period 1951 to 2005. There has also been a steadily increasing trend in maximum temperature in the country with values ranging from 31 to 33OC, with marked regional variations between the north and the south. In the north, maximum temperature values lie between 32 to 35°C while in the south, values lie between 30 to 33OC. Minimum temperature has generally increased slightly faster than the maximum temperature resulting into smaller temperature range.
The mean annual variability and trend of rainfall over Nigeria in the last six decades depicts the existence of a number of inter-annual fluctuations that have been responsible for dry and wet years or extreme climate events such as droughts and floods in many parts of the country and at different times. The period 1970 to 1990 was dry except between 1978 to 1980 and coincided with the Sahelian droughts of early 1970s and 1980s. From 1990s to present, rainfall has been above normal. However, despite this general recovery in rainfall since 1993, the general trends show slight decrease in rainfall especially since 2001 and particularly in the extreme northern part, even though some locations have been experiencing some extreme rainfall events in the very recent years.
Using climate models, many researchers have simulated future climate projections for Nigeria. Their scenarios suggest that there will be an increase in temperature of approximately 0.02OC to 0.04OC per year from 2000 until 2100 over the entire country. Higher temperature increase is expected over the inland regions compared with the coastal regions, with the level of the change increasing with latitude. Heat waves (when the maximum temperature is greater than 35OC for three days or more consecutively) are projected to occur more frequently over the entire country in the future. The future projections predict a wetter climate in the south (at least 0.2 mm/day south of 8°N) and a drier climate in the north.
Based on the above analysis and projections, we can say that climate change will magnify natural disasters’ severity in terms of intensity and frequency in Nigeria, but the nature and severity of the changes must be properly diagnosed. Increasing frequency of extreme weather events evident in terms of floods and drought in Nigeria is attributed to observed changes in the climate of the country. Major floods (e.g. 2012), with return period of 100 years, now takes place every 10 or 20 years. As more intense rainstorms are projected to hit many parts of Nigeria because of climate change, there will simply be more water and catastrophic floods will become regular events. On the other hand, extreme droughts, linked to climate change, have become regular features in the northern part of the country. How vulnerable Nigeria is or will be to these changes will be highlighted in the next article.
(People who are interested in additional technical details can read (1) Abiodun, B. J., Salami, A. T. & Tadross, M. (2011). Developing Climate Change Scenarios: Biophysical Impacts and Adaptation Strategies in Nigeria. Ibadan, Nigeria: Nigerian Environmental Study/Action Team (NEST); (2) Afiesimama, E. A., O. F. Ati, J. O. Olokor, M. A. Ijioma, M. A. C. Chendo and A. Ayansina (2010): National Climate Change Scenarios Development. Draft Technical Report for Nigeria’s Second National Communication; (3) Cervigni, R., Riccardo, V., and Monia, S, eds. 2013. Toward Climate-Resilient Development in Nigeria. Directions in Development. Washington, DC: World Bank; (4) Karmalkar, A., McSweeney, C., New, M and Lizcano, G., 2010: The UNDP Climate Change Country Profiles: Nigeria. Available at http://country-profiles.geog.ox.ac.uk; and (5) OECD (2007): Atlas on Regional Integration in West Africa: Climate and Climate Change)
By Prof. Emmanuel Oladipo (Climate Change Specialist and Adjunct Professor, Department of Geography, University of Lagos, Nigeria. Email: firstname.lastname@example.org)