How do we know if the global warming in the twentieth and twenty-first centuries is an anomaly, or just part of a natural cycle?
Tree ring growth can be absolutely dated, and mapped onto a historical timeline. This tree ring data shows that the temperature changes we have experienced in the twentieth and twenty-first centuries are unprecedented in terms of speed, and are global.
Professor Mary Gagen, of Swansea University’s Geography Department, measures tree ring data – ‘weather stations across the world’ - to find out what has happened to our climate across the planet over the last few thousand years.
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