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Summary and implications

Increasing concentrations of atmospheric carbon dioxide and other greenhouse gases are a serious threat to New Zealand’s marine ecosystems, and the benefits we receive from the marine environment. New Zealand’s subantarctic waters have become increasingly acidic since measurements were first taken in 1998, and long-term data show sea-surface temperatures in New Zealand’s waters have been increasing over the last century. Sea levels around New Zealand’s coastline have risen since reliable measurements began in 1900, at a rate consistent with sea-level rise worldwide.

Ocean acidification and ocean warming have the potential to cause widespread changes to ecosystems and biophysical processes – often through complex interactions with other environmental stressors and climate change impacts. Increased storminess and changes in ocean currents – and other pressures – such as sedimentation, algal blooms, and marine pests – may have compounding effects. These changes will bring challenges and opportunities to industries such as aquaculture and fisheries, and changes to recreational fishing and Māori harvesting of mahinga kai (traditional food). Sea-level rise is already affecting our coastline and will continue to do so.

These changes to our marine environment are evidence of human beings’ profound impact on Earth’s natural systems. Ocean acidification will continue for generations if substantial carbon dioxide emissions from human activities continue. Ocean warming and sea-level rise are set to continue for centuries to millennia even if global greenhouse gas concentrations are stabilised. While these future changes to the state of our marine environment are largely inevitable, the rate, and extent of change, will depend on whether, and how fast, human societies reduce greenhouse gas emissions on a global scale.

Extracting fossil fuels and other resources from under the sea has a localised impact

The burning of fossil fuels is a major cause of anthropogenic (human-induced) global warming and ocean acidification. On a local scale, the extraction of fossil fuels such as oil and gas from ocean-based wells can have environmental impacts.

In 2012, about 197 offshore oil and gas wells were drilled in New Zealand waters, 176 of which are in the Taranaki region (Petroleum Exploration and Production Association New Zealand, 2015).

Oil and gas extraction can adversely affect the marine environment, although the effects are localised. Offshore and deep-sea oil and gas extraction and transport always carry the risk (however small) of a major oil spill, which, based on overseas events, can cause devastating and widespread harm to the marine environment.

Potential sites for mineral extraction are being surveyed and explored. Sediment plumes produced by the extraction process can affect an extensive area, as the suspended sediment spreads. The plumes reduce food availability for some species, smother seabed species such as corals, and reduce light availability for photosynthesis. Discharge of tailings (residues from extraction) and effluent can harm plankton and fish species (Chung et al, 2002; MacDiarmid et al, 2012b).

For international comparability of the marine economy, ‘offshore minerals’ includes oil, gas and minerals, but in practice this grouping is primarily oil and gas. In 2013, offshore minerals contributed $1.95 billion to New Zealand’s gross domestic product; it made up 48 percent of the marine economy and 0.9 percent of the national economy (Statistics NZ, 2016a). Most of the oil and gas used by New Zealanders is imported from overseas.

For more detail see Environmental indicators Te taiao AotearoaOccurrence of oil and gas and minerals extraction.