Sea surface temperature increases
To monitor fluctuations in sea surface temperature
Mean annual sea-surface temperature collected from Voluntary Observing Ships (VOS) between Struisbaai to Knysna up to 60 nautical miles offshore, 1903–2013
Source: Southern African Data Centre for Oceanography (SADCO).
Are we making progress?
Sea-surface temperatures of southern Africa appear to have increased by about 0.25°C per decade over the last four decades and analysis of data collated from Voluntary Observing Ships (VOS) from 1903 to 2013shown on the graph.
Changes in sea temperature can severely affect marine ecosystems and productivity. As sea-surface temperatures rise, marine species are expected to respond by shifting their distribution patterns, particularly those species that are most sensitive to temperature. Fish species from the east coast are expected to invade waters further south in greater numbers, while the distributional ranges of species in the cooler west coast waters may retreat to greater depths, or become restricted to the immediate vicinity of bodies of upwelled water (through a process whereby cold water is brought to the surface near the coast under the influence of longshore equatorward winds).
An increase in sea-surface temperature is also correlated with a rise in sea level, with increases of 10–15 mm having been measured over the last century. Tide gauge measurements from South Africa indicate that sea levels have risen by approximately 1.2 mm/annum over the last three decades and this trend is expected to accelerate in future, with recent estimates suggesting a 12.3-cm rise by 2020, a 24.5-cm rise by 2050, and a 40.7-cm rise by 2080.
The potential impacts on coastal environments include increased coastal erosion, inundation, increased salt water intrusion, raised groundwater tables, and increased vulnerability to extreme storm events.
The direct effects of rising sea levels on the ecological functioning of marine biota are less obvious and, while some regions might be directly harmed (for example, salt marshes), others are predicted to undergo shifts in distribution patterns and/or zones (for example, rocky shores) where such shifts are still possible.