It is widely accepted that climate change is occurring, temperatures have risen 0.13°C per decade since 1956 (IPCC, 2007). But the cause of this rise has been under debate. A reason could because of natural climate variability. Global temperatures have varied throughout the earth’s history, for instance during the Pliocene temperatures were 2-3°C higher (Dowsett et al., 1994) and during the last glacial maximum temperatures were 4-7°C lower (Waelbroeck et al., 2002). It has been hypothesised that the effects of increased CO2 could be negligible compared to that of natural climate change (Hulme et al., 1999). However the most likely reason for recent climate change is the increase in the amount of CO2 and other greenhouse gases (GHG) being pumped into the atmosphere. GHG emissions have increased 70% since pre-industrial times (IPCC, 2007) and the concentrations of GHGs in the atmosphere are well outside their natural range (IPCC, 2007).
Climate change has several implications for the ocean, for instance more CO2 will be absorbed from the atmosphere creating a more acidic ocean, increased temperatures cause a reduction in land ice resulting in a larger volume of water entering the ocean, and increased water temperatures will cause thermal expansion of the water molecules hence sea level rise. This section discusses how these effects of climate change will affect coral reefs. The effects of ocean acidification, sea level rise, warmer seas and increased frequency of storms will all be described.