ASTONISHING though it may seem, it turns out that libraries of old books and newspapers are also a record of atmospheric conditions at the time the trees that went into their making were grown.
By analysing the carbon isotopes in bits of paper clipped from old magazines, an American professor, Dan Yakir, has traced the rising effects of atmospheric pollution from burning fossil fuel, dating back to the beginning of the industrial revolution.
Scientists generally reconstruct the record of past climate change from sources such as ice cores or tree rings.
But a reliable tree-ring history, says Yakir, requires an analysis of quite a few trees.
Yakir said: “Rather than going to forests all over the world to sample trees, we went to the local library.”
In the library of the institute where he works, Yakir found issues of the scientific journals Science, Nature and the Journal of the Royal Chemical Society, going back over 100 years to the late 19th century.
He then took small samples from the margins of successive volumes to the lab for detailed analysis.
The analysis was based on a finding that the proportion of a carbon isotope – carbon 13 – to its lighter counterpart – carbon – could provide information on the CO2 added to the atmosphere from burning fossil fuel.
This is based on a cycle that begins with plants taking up CO2 in photosynthesis.
All plants prefer to use CO2 made with the more common carbon 12 than carbon 13.
Plant biomass from millions of years ago was transformed into reservoirs of oil, gas and coal, and so these are naturally low in carbon 13.
Yakir: “When we started to burn those reservoirs after the industrial revolution, we began returning the carbon 13 CO2 to the atmosphere.
“Now the atmospheric carbon 13 content has become increasingly diluted, and this, in turn, is reflected in the carbon ratios in the trees milled for pulp and paper.”
Yakir’s work shows that this continuing dilution is, indeed, clearly recorded in the archival paper.
Plotted over time, it demonstrates the increasing intensity of our fossil fuel burning in the past 150 years.