Is carbon-14 still increasing in the atmosphere?

Question

One argument used to support the idea that the age of the earth is on the order of 10,000 years old (the 'young earth hypothesis') is that radiocarbon dating is confounded by the fact that the levels are not stable, and that the concentration of carbon-14 in the atmosphere is still increasing in our current atmosphere.

This argument is presented by Dr. Kent Hovind and his ministry of Christian Science Evangelism in two writings posted at his website, (www.drdino.com):

1. Wrong assumptions in C-14 dating methods.
2. Does carbon dating prove the earth is millions of years old?

In [2], Dr. Hovind states:

Present testing shows the amount of C-14 in the atmosphere has been increasing since it was first measured in the 1950s.

No sources were provided of course, thus I'm interested in knowing: Are the current levels of carbon-14 on the rise? and how can one test for this?

Answer 1

Background

There are two major sources of 14C in the atmosphere:

1. solar radiation
   • affected by sun spots (small magnitude, decadal time scales)
   • earth's magnetic field can deflect solar radiation (effect has a larger magnitude and occurs on millennial time scale)
2. nuclear weapons tests (large magnitude effect, can change quickly, affected by technology and politics)

There are also sources of CO2 that is depleted in 14C relative to the atmosphere. Atmospheric 14C can be reduced by the release of low 14C carbon, because this input dilutes the atmospheric signature. Because 14C has a half life of 5000 years, only 0.5^(age_x/5000) times the initial 14C will remain at age_x.

CO2 that is depleted in 14C comes from:

1. The burning of fossil fuels is the most important source of 14C depleted CO2
2. Historically, increased soil temperatures and reduced glacial coverage have released depleted CO2 from soils
3. The circulation of the ocean brings 'old' CO2 from the deep ocean to the surface, where it exchanges with 'new' CO2 in the atmosphere.

There are two major sinks of CO2 from the atmosphere, these sinks remove 14C CO2 in proportion to its atmospheric concentration:

1. photosynthesis (plant and algae), some of which is buried or sink in the ocean
2. being dissolved in the ocean

Finally, the average time that a molecule of CO2 remains in the atmosphere is between 5 and 200 years (IPCC 2007 table 2.14), so after an anomalous change, the concentration of 14C in the atmosphere will return to equilibrium with sources and sinks over time. This can be seen in first figure below.

In the figures below, the y axis is Δ14C. Δ14C is the per-mil (parts per thousand) deviation in the 14C content of CO2 relative to the pre-weapons testing atmosphere (c. 1950).

Further introduction and technical references can be found at Dr. Fiona Petchy's website, references with a global change emphasis can be found at the Radiocarbon in Earth System Science Short Course website.

Answer

[14C_atm] has been declining since the bomb spike

14C increased sharply (first figure) from the 1940s through the early 1960's due to the peak in nuclear tests. Since the atomic weapons ban treaty, atmospheric 14C levels have been steadily declining, but the rate of this decline has been slowing as atmospheric 14C reaches equilibrium with other sources and sinks. This is primarily the result of:

1. the uptake of CO2 by the biosphere (plants, plankton)
2. exchange with older CO2 in the ocean and
3. the release of CO2 from fossil fuels into the atmosphere (radiocarbon depleted in fossil fuels).

A classic paper on this is Nydal and Lövseth (1983), who report records of 14C in the atmosphere - observed at a range of sites from 78N to 21S between 1960 to 1981. They demonstrate that the shape of the 14C 'bomb spike' is consistent across latitudes as well as the expected effects of atmospheric mixing between hemispheres and between the free atmosphere and the ocean surface.

Measurements at the ocean surface are relatively lower because this is where CO2 from the atmosphere is being exchanged with CO2 from the ocean, which much older and more depleted on average.

[14C_atm] continues to decline

Plenty of recent studies demonstrate that the decline continues to present. For example, Levin and Kromer (2004) provide a more recent analysis demonstrating that this trend continued into the 2000s:

The looooong (50ky) view

14C has been declining over longer time scales as well, as explained by Hughen et al 2004, resulting from a combination of changes in the earth's magnetic field, the release of 14C depleted CO2 from the deep ocean, and the coupling of atmospheric 14C-CO2 uptake by plants and old C release from soils that occurred during glacial retreat from 12ky ago to present.

For consistency with the above figures (keeping time from left to right), the direction of the x-axis in the figure below (years before present) is reversed. Original data available from NOAA. You can see the decline in 14C_atm that has accompanied the melting of the ice sheets (the last glacial maximum occurred approximately 20-25kya).

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Hughen, K.; Lehman, S.J.; Southon, J.R.; Overpeck, J.T.; Marchal, O.; Herring, C.; Turnbull, J. 2004. 14C Activity and Global Carbon Cycle Changes over the Past 50,000 Years. Science 303(5655)

Nydal, R., and K. Lövseth (1983), Tracing Bomb 14C in the Atmosphere 1962–1980, J. Geophys. Res., 88(C6), 3621–3642, doi:10.1029/JC088iC06p03621.

Levin, I., B. Kromer, H. Schoch-Fischer, M. Bruns, M. Münnich, D. Berdau, J.C. Vogel, and K.O. Münnich, 1994. δ14CO2 record from Vermunt. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

Levin, I., Kromer, B., 2004. The tropospheric and delta 14C level in mid-latitudes of the Northern Hemisphere (1959–2003). Radiocarbon 46, 1261–1272

Answer 2

To answer the secondary question 'How do you test for this', the simple answer is 'you count the percentage of radiocarbon atoms in a sample of air. Because there is not a great record of air (the amount in ice cores is too small for radiometric analysis), researchers often use plant material that was produced in a known year, reflecting the level of radiocarbon in the atmosphere when it was fixed by the plant.

what is measured if air is not available?

Wines (Burchuladze et al 1989; Schonhofer, 1992; Palstra et al 2008) and tree rings (Suess 1955) have been commonly used as proxies for atmospheric radiocarbon content at the time the plant material was produced.

Here is a comparison of 14C in wines (solid) and atmospheric (dotted) samples from Burchuladze et al (1989):

how is it measured The machine used to count the proportion of 14C is called an Accelerator Mass Spectrometer, an image from the Orange County Register is shown below:

references

Burchuladze et al (1989). Anthropogenic 14C variations in Atmospheric CO2 and Wines. Radiocarbon 31(3) 771-776

Palstra, S. W. L., U. Karstens, H.-J. Streurman, and H. A. J. Meijer (2008), Wine ethanol 14C as a tracer for fossil fuel CO2 emissions in Europe: Measurements and model comparison, J. Geophys. Res., 113, D21305

Schonhofer, Franze (1992) 14C in Austrian Wine and Vinegar. Radiocarbon 34(3) 768:771

Suess, H. E. (1955), Radiocarbon concentration modern wood, Science, 122, 415–417.

Answer 3

C-14 has error margins of a few thousand ans is accurate only up to 50.000 years. There are a few cases where the results are inconsistent, and these are the only experiments that are mentioned by your source or creationists generally. For example the The (2300 year old) mollusk incident is explained in full detail by Keith and Anderson (1963), and has no impact on the general reliability of carbon dating.

Even with the worst kind of error margin applied to some of the older datings, it's nowhere near the proposed 6000-10000 years, creationists talk about.

According to paleontologist Niles Eldredge (1982:103), there have been thousands of dating tests performed by independent laboratories and a wide variety of radioisotopes. Virtually all of the results correlate with evolutionary expectations. The comparatively few anomalies in radiometric dating tend to vanish when the samples are reanalyzed.

Using carbon-14 to find out the age of the world is unsuited, as the upper-age-limit is about 50.000 years. But there are other radioisotopes that allows more accurate dating for dating really old material.

Scientists used Uranium-lead dating to specify the age of the earth. Meteorids have been tested undependently and the result is an age of about 4.54 Billion years. Of course, scientists can't pin the origin of earth down to a single year, as the error margins are about 1.2%, that means ±50 Million years. That sounds like a lot but:

A few million years sounds like a huge error, but a couple of million years one way or the other is a small error compared with the huge age calculated. Saying '380 million years plus or minus two million' is like thinking back to April from December and saying you can't remember whether something happened on the 19th, 20th, or 21st. (Eldredge 1982:103)

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Berra TM. 1990. Evolution and the Myth of Creation. Oxford: Oxford University Press.

Keith MS and Anderson GM. 1963. Radiocarbon dating: fictitious results with mollusk shells. Science 141:634.