Top issue – global greenhouse gas emissions are causing ocean acidification and ocean warming
Global greenhouse gas emissions have increased concentrations of greenhouse gases in the atmosphere to unprecedented levels in human history (IPCC, 2013), warming the planet, including the world’s oceans. The world’s oceans have become more acidic as they have absorbed additional carbon dioxide in the atmosphere from human activities. These changes are also occurring in New Zealand’s waters.
Based on global projections, ocean warming is set to continue for centuries to millennia, even if global greenhouse gas concentrations are stabilised (IPCC, 2013). Ocean acidification will continue for generations if substantial emissions from human activities continue (IPCC, 2013). The rate and extent of change to New Zealand’s oceans over centuries will depend on whether, and how fast, human societies reduce global greenhouse gas emissions.
Ocean acidification and warming may cause widespread harm to marine ecosystems, for example, by reducing the survival and growth rates of marine species, extending or reducing the range of species, and modifying habitats. These impacts could occur across New Zealand’s entire ocean area, with implications for biodiversity, Māori harvesting of mahinga kai (traditional food), and marine-based industries such as aquaculture and commercial fishing.
Ocean warming is a primary cause of rising sea-levels. Sea-level rise is a long-term threat that will increasingly affect coastal marine habitats. It has substantial implications for coastal housing and infrastructure.
Global greenhouse gas emissions, largely from burning fossil fuels, are changing our marine environment
- Global net greenhouse gas emissions rose 33 percent from 1990 to 2011. New Zealand’s overall contribution to global emissions is small; however, our emissions per person are among the highest in the world.
- New Zealand’s subantarctic waters have become more acidic since measurements were first made in 1998. This ocean acidification is consistent with changes measured elsewhere in the world.
- Sea-surface temperatures in New Zealand’s waters showed a statistically significant increase of about 0.71 degrees Celsius over the period 1909–2009. The increase is consistent with global average sea-surface-temperature increases. Annual average sea-surface temperatures around New Zealand measured by satellite over the past 20 years show no determinable trend. This is not surprising, as over short time scales natural variability can mask any long-term trends.
- Sea levels around New Zealand’s coastline have risen between 1.31 and 2.14 millimetres a year on average since reliable measurements began in 1900, at a rate consistent with sea-level rise worldwide.