The measurement of atmospheric carbon dioxide (CO₂) reaches a milestone this week. NIWA's globally significant Baring Head Clean Air Observation Programme is celebrating 40 years of continuous monitoring.

This now iconic CO₂ time series was started in order to investigate the influence of human CO₂ emissions on climate. The first measurements were made on 14 December 1972.

Baring Head has the second longest continuous measurement record in the world. It is the longest in the Southern Hemisphere.

Sitting at the top of a cliff near the southern tip of Wellington Harbour, the site is exposed to strong southerly winds, bringing clean air that has not been in contact with land for at least five days.

There are few stations in the Southern Hemisphere. Baring Head is a clean air background site that contributes an important part of the global picture because it is presentative of large areas of the mid-latitude Southern Hemisphere.

NIWA programme leader Dr Mike Harvey says, "We want to know how the concentration of CO₂ in the atmosphere changes over time, in relation to what we are emitting into the atmosphere. A proportion of what we emit stays in the atmosphere and by measuring that precisely we have a better understanding of how much energy is trapped in the atmosphere as a result of these greenhouse gases, and hence the expected rate of global warming."

The long term trend from Baring Head of atmospheric CO₂ indicates that the amount of CO₂ in the atmosphere is continuing to increase each year, with growth rates currently of around 2 ppm (parts per million), or 0.5%, every year. There is 20% greater CO₂ content in the atmosphere now (390 ppm) than when the measurement series started (325 ppm).

The first continuous atmospheric CO₂ measurement station was established in the late 1950s by Dr Charles Keeling of Scripps Institution of Oceanography in California. It began a series of continuous atmospheric CO₂ measurements at a mountain top site at Mauna Loa in Hawaii.

Keeling was behind the initiatives that got New Zealand's CO₂ programme underway. In 1969, Charles Keeling and colleagues worked with the DSIR in Lower Hutt and initiated a joint project which saw Dr Dave Lowe and colleagues make continuous atmospheric CO₂ measurements. To keep this research going for 40 years has required an evolving and dedicated team, now led by NIWA's Gordon Brailsford.

These early measurements showed a pronounced seasonal cycle caused by uptake and release of CO₂ by the biosphere, but they also conveyed a compelling message of the rapidly increasing burden of CO₂ in the atmosphere.

Since the establishment of Baring Head, DSIR and NIWA expanded research into the measurements of the major greenhouse and other trace gases. NIWA makes significant measurements at its Lauder site in Central Otago, Rainbow Mountain near Rotorua and Arrival Heights in Antarctica.

NIWA is a significant contributor to an international network of stations called the Global Atmosphere Watch (GAW) Network. Baring Head contributes to the GAW programme which is coordinated by the World Meteorological Organisation.

At Baring Head, the scientists sample gases using a number of cutting-edge techniques.

"In New Zealand, we are at the forefront of the use and understanding of new technologies. We use laser technology to make the raw measurements of CO₂ and methane once every few seconds. Currently, our research is combining measurements at Baring Head and other sites in the region within a meteorological modelling framework to estimate the regional distribution of sources and sinks of CO₂," says Dr Harvey.

The effect of global action on mitigation of CO₂ emissions will become apparent in the record in the coming decades.

Dr Harvey says, "As the century progresses we could move to quite a different climate to what we have today. If emissions of CO₂ continue unabated then later in the century major global economic impacts are expected from changing rainfall patterns from the changing severity of climate change extremes."

For the latest data from Baring Head see 

https://www.niwa.co.nz/atmosphere/our-data/trace-gas-plots