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- Life on Earth depends on the protective properties of the ozone
layer and the 'greenhouse' gases in the upper atmosphere (water vapour,
carbon dioxide, methane, and nitrous oxide). The ozone layer filters
harmful ultraviolet radiation while the greenhouse gases keep global
temperatures within a liveable range. Recently, ozone levels have
fallen while greenhouse gases have increased.
- Potential problems arising from ozone depletion include the increased
risk of impaired growth and reproduction in some plants, including
crop plants, and of eye and skin problems in some humans and other
animals as a result of more intense ultraviolet-B radiation.
- Scientists working with the Intergovernmental Panel on Climate Change
(IPCC) now believe that the release of greenhouse gases from human
activities is causing global temperatures to rise and weather patterns
to change. Potential problems arising from this are more frequent
floods and droughts, land encroachment and coastal erosion from rising
seas, more frequent invasions by tropical pests, weeds and infectious
diseases, and the disappearance of some types of ecosystems. In New
Zealand, patterns of agriculture may be changed and some fisheries
may be affected.
- Ozone concentrations in the upper atmosphere have been significantly
depleted over the past 20 years by manufactured gases that contain
chlorine (such as chlorofluorocarbons, known as CFCs). The total concentration
of chlorine in the atmosphere has grown by more than 600 percent from
its natural level of around 0.6 parts per billion to an unprecedented
4.0 parts per billion.
- At mid latitudes, total ozone has declined by an average 4-5 percent
over the past 20 years. Above the Antarctic, a 'hole' in the ozone
layer has occurred every spring since the 1980s. By 1995, it had expanded
to its maximum possible area but had not yet reached its lowest possible
ozone concentrations. The hole (which does not directly affect New
Zealand) is likely to keep reappearing until the middle of the next
century, until atmospheric chlorine levels have been brought back
down to about 2 parts per billion.
- Coinciding with the depletion of the ozone layer, the levels of
solar ultraviolet (UV) radiation in New Zealand have been increasing.
Monitoring is relatively recent, and only limited data are available,
but it is estimated that a 5-7 percent decrease in ozone since the
mid 1970s has been accompanied by a 6-9 percent increase in ultraviolet-B
- Greenhouse gases other than water vapour have increased worldwide
in the past several hundred years, as a result of increased industrial
and agricultural production, and motor vehicle use. Water vapour is
also expected to increase as global temperatures rise, causing more
- Carbon dioxide (CO2) concentrations have increased by
about 30 percent since pre-industrial times with Southern Hemisphere
concentrations lagging slightly behind the Northern Hemisphere.
- On a per capita basis, New Zealand emissions of human-induced carbon
dioxide are 25 percent lower than the OECD average, but about 50 percent
higher than the global average. At present, about half of these emissions
are absorbed by forest growth which acts as a 'carbon sink'. The area
of commercial pine forests is increasing at present, but in the long-term
the forests will not be able to maintain the 50 percent absorption
ratio unless reductions are made in actual carbon dioxide emissions.
- Globally, atmospheric methane (CH4) concentrations have
more than doubled in the past 400 years. Methane is produced by biological
processes (e.g. sheep and cattle digestion, rice growing, and the
breakdown of waste) and fossil fuel production and use. The global
rate of methane increase slowed during the 1980s and early 1990s,
but has been rising again since 1993.
- New Zealand's per capita emissions of methane are almost six times
the OECD average, and almost ten times the global average. Although
cattle and deer numbers are increasing, the recent fall in sheep numbers
caused a reduction in livestock methane emissions of 3.5 percent between
1990 and 1995.
- Nitrous oxide (N2O) concentrations are increasing globally
but the sources are dispersed and not well understood.
- The atmospheric changes of the past century have coincided with
small changes in average global temperature and sea level. Surface
temperatures have increased by between 0.3°C and 0.6°C since
1900, and by between 0.2°C and 0.3°C in the last 40 years.
Global sea level has risen by between 10 and 25 cm over the past 100
years, and much of that rise may be related to the increase in global
- Scientists increasingly suspect that the two trends are linked,
and have attempted to disentangle the climatic effects of human-induced
atmospheric change from those of natural factors (e.g. the short-term
effects of sunspot cycles and sulphate particles emitted by industry,
volcanoes and marine algae, and the long-term effects of fluctuations
in the Earth's axis and orbit).
- Although there are still scientific uncertainties, and although
recent global warming still falls within the range of natural variability,
the Intergovernmental Panel on Climate Change (IPCC) has concluded
that 'the balance of evidence suggests that there is a discernible
human influence on global climate'. The latest IPCC report predicts
global warming in the range of 1°C-3.5°C over the next century
and a sea level increase of about 50 centimetres.
- New Zealand's climate has warmed faster than the global average,
gaining 1. 1°C since 1860, compared to the world's 0.7°C.
Most of this warming has occurred in the last 50 years. Prior to 1940,
there was little discernible trend. Our sea level has risen by 15
centimetres in the past century.
- Scientists are uncertain about the potential interaction of climate
warming with the El Niño-Southern Oscillation (ENSO). This
recurrent climatic pattern periodically makes New Zealand cooler,
drier, and more prone to cyclones. It is triggered by changes in surface
air pressure over the Pacific Ocean and alters ocean currents, rainfall,
winds and temperatures around the world. Some scientists suspect that
ENSO events may increase in frequency or duration as the climate warms.
- New Zealand's general response to human-induced pressures on the
atmosphere has been to participate in international efforts to reduce
damaging emissions and to contribute to international research on
the problems (e.g. through regular monitoring of the atmosphere at
Baring Head in Wellington, Lauder in Central Otago, and Scott Basein
- In particular, New Zealand has responded to the ozone threat by
agreeing to the restrictions on ozone-depleting substances set down
in the international convention known as the Montreal Protocol, and
has set even more stringent domestic goals for phasing out the use
of chlorofluorocarbons (CFCs) and several other harmful substances.
- CFC use is declining, both here and overseas. New Zealand's use
per person in 1993 was half that of the OECD, but still twice the
global average. Our national use of CFCs had always been below the
internationally-agreed limits set by the Montreal Protocol, but in
accordance with the Protocol, consumption (imports) ceased on 1 January
- Ozone is a naturally occurring greenhouse gas and has always been
part of the natural greenhouse effect. What effect the restoration
of ozone to pre-CFC levels will have on global warming is unclear.
This is because of the uncertainties relating to future levels of
greenhouse gas emissions from human activities; the fact that although
the substances replacing CFCs are not ozone-depleters, many of them
are powerful greenhouse gases, and because of the overall complexities
of atmospheric physics.
- New Zealand has responded to the greenhouse threat by signing the
Framework Convention on Climate Change (FCCC) and setting the domestic
goals of reducing net carbon dioxide emissions to their 1990 levels
by the year 2000 and stabilising them from then on.
- Since 1990 our net carbon dioxide emissions have actually risen,
despite increases in forest planting. The main causes have been increasing
fossil fuel use associated with economic growth, and changing forest
growth rates associated with age structure. Current projections indicate
that, in the absence of further policy measures, our net CO2
emissions will be more than double 1990 levels by the year 2000.