Long-term studies show carbon dioxide1 levels in the atmosphere2 are rising. Radiocarbon carbon3 dioxide peaked in the 1960s but has since decreased. Much has been taken up by the ocean. Dr Kim Currie of NIWA is one of the scientists measuring this.
Radiocarbon in the atmosphere
In 1954, Athol Rafter and Gordon Fergusson started measuring radiocarbon carbon dioxide (14CO2) in the air at Makara, near Wellington. Sampling has since moved a few kilometres to Baring Head and different scientists are involved, but data4 is still collected every month. This makes it the longest continuous record of its kind in the world. Since 1970, ‘normal’ carbon dioxide has also been measured – the longest running record in the southern hemisphere. The only atmospheric carbon dioxide recording that has been going on for longer is at Mauna Loa, Hawaii, which started in 1958.
Kim Currie of NIWA, based in Dunedin, is one of the scientists involved in carrying on the measurement of atmospheric 14CO2. This ties in with her other research on CO2 in the ocean around New Zealand. It is difficult to study one without the other, as carbon dioxide is constantly being exchanged between the ocean and the atmosphere as part of the natural carbon cycle
The data collected by Kim and her team is added to models that try to explain changes observed over the last 60 years. These models, built up from data from all round the world, are also used to try and predict future changes in the atmosphere and ocean.
Bomb radiocarbon
Atoms of the element5 carbon come in several forms, called isotopes6. Most carbon has a nucleus7 with 6 neutrons and 6 protons, written 12C. Some carbon atoms have 8 neutrons and 6 protons, written 14C. This isotope8 is radioactive9 and is often called radiocarbon. The radioactivity10 of 14C means that it can be detected amongst all the non-radioactive 12C.
Most carbon dioxide in the atmosphere is made from 12C, but small amounts of 14C carbon dioxide (14CO2) also occur naturally. In the late 1950s and early 1960s, humans added a lot more radioactive 14C to the atmosphere through the testing of nuclear weapons. This is often called ‘bomb radiocarbon’. There was a Test Ban Treaty in 1963, but France carried on testing until 1968 and China until 1980. One good thing came of all this – scientists have been able to study the carbon cycle11 by following what happens to the extra 14C.
14CO2 in the carbon cycle
12CO2 in the atmosphere has risen steadily since the 1950s, as shown by data from Baring Head and other places around the world. On the other hand, 14CO2 has been decreasing since testing of nuclear weapons stopped.
So where is all the 14CO2 going? It will take thousands of years for it all to be lost through radioactive decay12, so there must be other reasons for the decrease. Research shows that most of the bomb radiocarbon has been taken up by the ocean and most of the rest by plants and soil on land. Early models suggested that the ocean would take up so much 14CO2 that it would start giving it back to the atmosphere. This proved to be true – by the early 2000s, the level of 14CO2 in the atmosphere levelled out, suggesting that the amounts of 14CO2 moving from ocean to atmosphere and from atmosphere to ocean were balanced.
Another clue to what has made the 14CO2 in the atmosphere go down is that the 12CO2 has gone up. The addition of lots of 12CO2 to the atmosphere, mainly from the burning of fossil fuels13 by humans, has diluted the 14CO2. Fossil14 fuels do not contain 14C because it all decayed away long ago.
Nature of science
Not all progress in science is made by sudden ‘discoveries’. It is only because of long-term collection of data at places such as Baring Head, Wellington, that scientists have been able to observe important patterns. With the current interest in global warming, the graph of atmospheric carbon dioxide increase at Manua Loa has become famous. It is called the Keeling curve, named after the person who started the project.
Related content
The ocean, CO₂ and climate change covers some important historical dates in the history of ocean studies, including the interaction of the ocean with climate and atmospheric carbon dioxide.
In the Connected article Trees, seas and soil discover what a carbon sink15 is and why they are so important.
Activity idea
In Using radiocarbon carbon dioxide data students interpret graphs showing carbon dioxide in the atmosphere of New Zealand and explore how sampling intervals affect the conclusions we are able to make.
Useful link
Read and listen to this Radio NZ article and podcast about Carbon Watch NZ – a collaborative project to measure New Zealand's greenhouse gases16 and a fascinating history of 50 years of CO2 measurements.
NASA's Eyes on the Earth site shows the positions of their Earth observation satellites. Use the tabs at the bottom of the page to filter for greenhouse gases17 and other measurements.
- carbon dioxide: CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.
- atmosphere: 1. The layer of gas around the Earth. 2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.
- carbon: A non-metal element (C). It is a key component of living things.
- data: The unprocessed information we analyse to gain knowledge.
- element: A substance made of atoms that all have the same atomic number. Elements cannot be split into simpler substances using normal chemical methods.
- isotope: Different forms of atoms of the same element. Within the nucleus, there is the same number of protons but a different number of neutrons, giving each isotope a different atomic mass.
- nucleus: 1. The very small, very dense, positively charged centre of an atom containing protons and neutrons. 2. Part of the cell that contains the cell’s hereditary information (DNA) and controls the cell’s processes.
- isotope: Different forms of atoms of the same element. Within the nucleus, there is the same number of protons but a different number of neutrons, giving each isotope a different atomic mass.
- radioactive: Giving off energy as a result of the breaking up of nuclei of atoms. Something undergoing radioactive decay, the process by which an unstable atom emits radiation.
- radioactivity: The spontaneous emission of radiation from an atom’s nucleus.
- carbon cycle: The process by which carbon passes through the natural world.
- radioactive decay: The process in which an unstable atomic nucleus loses energy by emitting radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide, transforming to an atom of a different type, called the daughter nuclide. The average time interval required for one-half of any quantity of identical radioactive atoms to undergo radioactive decay is called half life.
- fossil fuel: Materials such as coal, oil and natural gas formed from the fossilised remains of plants that lived many millions of years ago. Often burned as fuel – although this releases large amounts of CO2, which contributes to global warming. Fossil fuels are also not renewable – there is a limited amount.
- fossil: The remains or imprint of an organism preserved in some manner. Typically fossils are found in sedimentary rock as a result of mineral replacement or imprinting in once soft silt or sand layers. Normally, rock fossils only include the hard parts of an organism such as the skeleton or shell. Fossils can also include the original remains (including soft tissue) preserved in amber, pitch or ice, or preserved in ‘fossil layers’ in special sheltered cave environments.
- carbon sinks: Natural storage sites for carbon that has been removed from the atmosphere, e.g. oceans absorb carbon dioxide from the air so are therefore called carbon sinks; trees and plant material temporarily store carbon dioxide.
- greenhouse gases: A natural or manmade gas that traps heat in the Earth's atmosphere and contributes to the greenhouse effect. The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone and industrial gases such as chlorofluorocarbons (CFCs). These gases in the Earth's atmosphere trap warmth from the Sun and make life possible. An overabundance of greenhouse gases leads to a rise in global temperatures – known as the greenhouse effect.
- gases: The state of matter distinguished from the solid and liquid states. Gases have the ability to diffuse readily and to become distributed uniformly throughout any container.