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The state of the data

The atmosphere is a shared resource and some of our information on it comes from international sources, such as NASA's Total Ozone Mapping Spectrometer (TOMS) and other satellite monitoring programmes operated by many countries, especially the European Community, the USA, and Japan. However, much of our data are also homegrown.

Records of temperature, rainfall, air pressure, and wind speeds have been kept at some sites in New Zealand for around 150 years. However, the technology for the routine measuring of trace gases has been developed only in the past few decades, spurred on by the increasing recognition of the need for such data. The early work was produced largely through the foresight and persistence of atmospheric scientists such as Edith Farkas, who meticulously monitored ozone from the 1950s until her retirement in 1986.

Further back than 150 years, New Zealand is fortunate in having considerable geological evidence of past atmospheric conditions and climate. These include sediment layers, fossilised pollen showing past vegetation patterns, geological evidence of glacier movements, tree rings, and bubbles trapped in ice. These have enabled scientists to reconstruct the Ice Age climate with a high degree of confidence.

Data on atmospheric gas levels

Today, trace gases in the atmosphere can be detected with a range of instruments so sophisticated that they make measurements in terms of parts per billion (ppb). Precise information on the concentrations of each gas can be gathered almost instantly. The National Institute of Water and Atmospheric Research (NIWA) does most of the measuring work on the stratospheric trace gases above New Zealand.

The carbon dioxide record established by Martin Manning and Peter Pohl began only in 1970, first at Makara near Wellington, then at the superior site at Baring Head, also near Wellington, in 1973. These data are representative of atmospheric carbon dioxide concentrations over a wide region of the ocean to the south of New Zealand. (See Figure 5.2).

Other tropospheric trace gases, such as methane, are also measured at the Baring Head Clean Air Sampling Station.

Total ozone is the amount of ozone contained in a vertical column of atmosphere up to 50 or 60 kilometres above a defined part of the Earth. It is most frequently measured in milli-atmosphere centimetres, or Dobson Units (DU). These take their name from the Oxford scientist G.M.B. Dobson, who, in 1920, also invented the instrument routinely used for today's ground-based monitoring of total ozone, the Dobson Ozone Spectrophotometer. New Zealand's ozone levels are monitored daily with one of these from the NIWA research station at Lauder, in Central Otago. A similar instrument at Scott Base measures ozone over Antarctica and plays an important role in the detection of the 'ozone hole' each spring. Since 1979, these ground-based measurements have been complemented by the satellite-borne Total Ozone Mapping Spectrometer (TOMS). Data from this, and other satellite instruments, are made available to scientists around the world.

CFCs, halons and other ozone-depleting chemicals in the atmosphere are not monitored in New Zealand. However, data on these chemicals are regularly obtained from overseas sources.

Figure 5.2: Typical southerly air flow to the Baring Head Clean Air Sampling Station, Wellington

Airflow to the Baring Head Clean Air Sampling Station which is located near Wellington is typically southerly.

Data on weather and climate patterns

Weather statistics are collected and maintained by both NIWA and MetService (the national meteorological organisation) from a network of monitoring stations around the country. They include data on rainfall, temperatures and sunshine hours. Prior to the 1980s, no data on ultraviolet (UV) radiation levels were available in New Zealand. In addition to the Robertson- Berger (R-B meter) which has been operating at Invercargill since the early 1980s, NIWA now operates three new-generation broadband filter R-B meters - two at Lauder, in central Otago, and one at Leigh, in Northland - as well as two spectroradiometers at Lauder.

To provide data on daily ultraviolet levels and make forecasts for public health purposes, Industrial Research Limited (IRL) has established a network of portable meters in main population centres.

Data on gas and particle emissions

Unfortunately, data on the quantity of emissions that we put into the atmosphere are not gathered as quickly or easily as data on atmospheric gas levels. Because there are many different sources of carbon dioxide, methane, CFCs, and other atmospheric contaminants, it is not possible to monitor them all. Instead total emissions must be estimated from other data on such things as the amount of fossil fuel produced or purchased (and presumably burnt, thereby emitting carbon dioxide), the amount of CFCs imported (and presumably used, thereby leading to emissions), and the number of ruminant animals (i.e. cattle, sheep, goats, deer) that are presumably burping methane into the atmosphere. Key emitters are usually sampled to assess the relationship between, for example, fuel use and the amount of pollution generated. Without this, accurate estimates could not be made, and even with this sampling the estimates still have a large degree of uncertainty. For carbon dioxide emissions from energy sources and industrial processes, however, emissions can be predicted to within about 6 percent.

Following this procedure, the Ministry of Agriculture provides annual calculations of methane and nitrous oxide emissions from agricultural sources. The Ministry of Commerce uses fossil fuel data to calculate greenhouse gas emissions from the energy sector (which includes electricity generation and transport, and CO2 from industrial processes).

Using forest planting data from the Ministry of Forestry, the New Zealand Forest Research Institute calculates the amount of atmospheric carbon which is absorbed by planted commercial forests. Each year, these calculations are combined by the Ministry for the Environment to reach an annual estimate of greenhouse gas emissions, including 'net' carbon dioxide emissions (that is, actual emissions minus the amount absorbed by forests).