Title of paper

1. Introduction to climate change¹

According to the United Nations Framework Convention on Climate Change (UNFCCC) - "climate change" means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.
In order to better understand climate change, it is necessary to start off with the definition of some of the basic terminologies that relate to climate change and that are sometimes misinterpreted in climate change discussions.

2. Common terminologies

2.1 Weather and climate change

Weather is the state of the atmosphere at a given time and place with respect to temperature, cloudiness, rainfall, wind, and other meteorological conditions.
Climate refers to the pattern of variation of the weather parameters over a time period. An accurate understanding of climate as well as the interaction between climate, the natural environment as well as socio-economic determinants is at the heart of addressing climate change.


Weather refers to conditions now; climate refers to conditions over a time period.
Meteorologists often point out that "climate is what you expect and weather is what you get".

2.2 Climate variability and climate change

Climate variability defines the way climate fluctuates above or below a long-term average value. A climatological normal period usually refers to 30-year average of a weather variable (e.g. temperature, precipitation).
Climate change refers to changes in the statistical distribution of weather patterns over time periods ranging from decades to millions of years. Climate change may be due to natural internal processes or external factors, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.
The ongoing climate change debate is mainly on the causes of climate change, rather than on the question of whether climate change is taking place or not. In its definition, the United Nations Framework Convention on Climate Change attributes climate change to direct or indirect human activities that alter the composition of the global atmosphere over time, in addition to natural internal processes. The proponents attribute the changes to the natural processes, and not necessarily to human induced factors.
Another common debate in Namibia is on the distinction between climate change and climate variability, and whether experienced climatic occurances (e.g. floods and droughts) are attributed to climate change or natural climate variability. The debate goes further into a discussion on the definitions of climatic conditions, e.g. drought, differentiating between scientific definition and political or socio-economic definitions.

Climate change is slow and gradual, is attributed to both natural processes and human induced factors. Climate variability is observed over a shorter time period and typically refers to natural changes in climate.

3. Detecting climate change

Climatologists look at long-term continuous changes (trends) in climatological averages and normals and the variety around these averages to detect changes in climate. In addition, they use modelling to predict future changes to climate.
General Circulation Models (GCM) are the fundamental tools used for assessing the past change and projecting change in the future. They are complex computer models, which represent interactions between the different components of the climate system such as the land surface, the atmosphere and the oceans. The models lead to a suite of possible futures, each of which is a valid representation of what the future climate may be. The key most important parameters studied in Namibia are changes in surface temperatures as well as rainfall. While predicting changes in temperature is easier, rainfall projections are much more difficult.
GCMs can usefully project into the future at a spatial scale of 200-300km (DRFN, 2008). This limits the application of GCM projections for assessments of change at the local scale (DRFN, 2008). To address the challenge, a technique of ‘downscaling’ is typically used to produce projections at a finer spatial scale. Downscaling relies on statistical relationships between the General Circulation Model large-scale circulation and historical data to project future changes from multiple GCMs.
According to the United Nations Framework Convention on Climate Change, it is widely recognized that there has been a detectable rise in global temperature (refer to figure 1), and especially during the last 40 years (DRFN, 2008). Importantly, this increase in the rate of change is expected to continue, potentially resulting in more rapid changes of climate in the future. The Intergovernmental Panel on Climate Change (IPCC) of the United Nations Framework Convention on Climate Change relates this global temperature change to human activities.



Figure 1: Changes in global temperatures. Source: DRFN, 2008.

As can be observed from figure 1 above, the regional distribution of temperature increases is not uniform and some regions have experienced greater change than others, especially the interior of continental regions such as southern Africa (DRFN, 2008). This is consistent with other studies done in southern Africa, e.g. detected increases in annual temperatures found over southern Africa since 1900 by Hulme et al. in 2001 (reported in DRFN, 2008). Additionally these changes in temperature are associated with decreases in cold extremes with increases in hot extremes.

To predict future climatic conditions, climatologists rely on historical trends as well as projections into the future.

Studies on historical trends and future predictions of climate change are limited. In 2008, the Desert Research Foundation of Namibia (DRFN) undertook a so-called Vulnerablity and Adaptation Assessment (V&A) on behalf of the Ministry of Environment and Tourism (MET) as part of the Second National Communication to the UNFCCC. The V&A assessment made predictions on how the climate of Namibia is expected to change in the future in terms of temperature and rainfall. The study relied on both historic climate data to understand past trends and to predict future changes. Most importantly, the study followed the UNFCCC definition of climate change and as such included potential human factors in the predictions. Given this consideration the following models were undertaken in addition to the climate modelling:

• 
  Crop modelling for specific regions (undertaken in collaboration with the Department of Agriculture)
  
• 
  Rainfall-runoff modelling for the Fish River basin (undertaken with the Department of Water Affairs and Forestry)
  

A summary of the results of this study is presented in section 3.2.