Climate variability and climate change – what is the difference?
The terms “climate variability” and “climate change” both refer to climate trends and patterns at a given period or simple space over time. Climate variability and climate change both affect agricultural productivity but their effects differ across crop types/cultivars and animal breeds and their adaptation.
Atmosphere is the layer of air surrounding the Earth, moving horizontally and vertically and thus causing variabilities in weather and climate. The most critical role played by the atmosphere on agricultural productivity is to protect the planet from high-energy radiation from the sun by trapping radiation to heat the earth and for photosynthetic processes in plants. Two key words for describing atmospheric conditions are “weather” and “climate”:
- Weather refers to the day-to-day state of atmospheric conditions in a short-term period from a few hours to about two weeks. It is the variation of climatological parameters such as rainfall, humidity, cloud and wind conditions.
- Climate refers to statistical information based on weather for a specific locality averaged over at least 30 years. It is a quantification of weather deviation focusing on a specified area for an identified interval. For example, Figure 1 gives an indication of how the atmospheric condition determines the soil water content and its impact on agricultural productivity.
Figure 1: Example of a maize field severely affected by prolonged dry spells.
Climate variability refers to the climatic parameter of a region varying from its long-term mean. The variations in the mean and standard deviation of the occurrence of extremes of climate on spatial and temporal scales are beyond that of individual weather events. The probable major driver of inter-annual climate variability and the equatorial Indian Ocean fluctuations in sea surface temperatures (SST) is known as the El Niño-Southern Oscillation (ENSO). The Oceanic Niño Index (ONI) is the primary indicator for monitoring El Niño and La Niña, which are opposite phases of the ENSO climate pattern. Moreover, the mode of variability that affects the western and eastern parts of the ocean is known as the Indian Ocean Dipole (IOD) index, which is the difference between SST anomalies in two regions of the tropical Indian Ocean. Figure 2 shows a negative ONI for 2020 representing cold period and negative IOD as occurred in 2019, thus indicating the fluctuations in warm and cold periods for different time series. The IOD has led to the worst droughts and bushfires; the negative phase is critical for bringing drought-breaking rain but the positive phase has more extreme climate impacts. The subtropical IOD events are large-scale SST anomalies that have a strong influence on South African rainfall. Warm SST in the west and cool SST in the east are related to low-level moisture advection over southern Africa and increased rainfall during the austral summer.
Figure 2: Oceanic Niño Index (ONI) and Indian Ocean Dipole (IOD) index prepared by the World Meteorological Organization (WMO).
Climate change points to the long-term fluctuations in rainfall, temperature, wind and all other climatological parameters. It refers to any change in climate over time, whether due to natural variability or anthropogenic forces and increasing greenhouse gas emissions. Therefore, it can be described as a change in climate, attributed directly or indirectly to human activity, which modifies the composition of the global atmosphere and, in addition to natural climate variability observed over comparable time periods, an observed change in average weather conditions. Climate change vulnerability refers to the degree to which a system is unable to cope with the adverse effects of climate change, including climate variability and weather extreme events. It is for such weather and climate challenges that the Agricultural Research Council Soil, Climate and Water (ARC-SCW) unit pursues its mandate to provide services such as climate data, early warning for climate disasters, adaptive technologies, crop suitability and soil/plant/water analyses.
Dr Gugulethu Zuma-Netshiukhwi
ARC-Soil, Climate and Water
E-mail: ZumaNetshiukhwiG@arc.agric.za
