In recent decades, global attention has focused on two environmental issues in relation to the atmosphere: climate change and depletion of atmospheric ozone. In response, the international community has acted to quantify and reduce emissions of greenhouse gases and ozone-depleting substances.
Atmospheric concentrations of carbon dioxide over New Zealand increased from 324 parts per million (ppm) in 1970 to 379 ppm in 2006. Atmospheric nitrous oxide concentrations showed an average increase of 0.9 parts per billion (ppb) each year over the last decade. Methane concentrations have shown a small reduction in recent years. These trends are in line with international trends.
In 2005, total emissions of greenhouse gases in New Zealand were 77.2 million tonnes of carbon dioxide equivalents. Between 1990 and 2005, total greenhouse gas emissions increased by 25 per cent, reflecting our growing population and economy. While New Zealand’s greenhouse gas emissions represent much less than 1 per cent of global emissions, we rank 12th per head of population.
New Zealand has an unusual profile of greenhouse gas emissions for a developed nation. Methane and nitrous oxide from the agricultural sector contribute nearly 50 per cent of our total emissions. Carbon dioxide emissions, largely from energy generation and transport, contribute most of the other 50 per cent. Many other developed nations have comparatively lower agricultural emissions, and higher emissions from energy generation.
Between 1990 and 2005, carbon dioxide removed from the atmosphere by forest growth (termed forest sinks) increased by 29 per cent, largely because of increases in plantation forestry in the mid-1990s.
In line with international trends, average New Zealand temperatures rose by 0.9°C between 1920 and 2006. This change means we can no longer take historical climate patterns as an accurate guide to the climate we will experience in the future.
As an island country reliant on primary production and tourism for its economic wealth, New Zealand will be particularly affected by climate change. Climate change is likely to bring about rising sea levels, an increase in floods and droughts, change wind and rainfall patterns, increase temperatures, reduce frosts, put pressure on our ecosystems, and increase the threat of pest species becoming established here.
Like many other developed countries, New Zealand is prioritising the development of a range of policies and initiatives to respond to climate change. In the future, the challenge will continue to be to reduce emissions from energy, transport, and the agricultural sector, and to increase afforestation. The need to adapt to both the positive and negative aspects of a changing climate is a challenge for all sectors.
In the 1980s, identification of the ozone hole over Antarctica led to international agreements to control the use of ozone-depleting substances. As a result, atmospheric ozone levels over Antarctica are now reducing more slowly than they were during the 1980s and 1990s, and ozone measured over Central Ōtago has stabilised since the late 1990s. The monitored summertime levels of ultraviolet radiation in New Zealand have tracked changes in ozone in recent years.
Ozone levels are expected to continue to improve as refrigerants and other chemicals that deplete the ozone layer are phased out in line with international protocols.