Evidence provides answers to climate questions

BRUCE Spittle asks two interesting questions about climate change (Letters, 31.10.19).

Why did Earth’s six major ice ages (spread over billions of years) take place when atmospheric carbon dioxide concentrations were much higher than today? Factors in addition to carbon dioxide were involved. These included a weaker sun, massive volcanic eruptions, and different configurations of the continents.

His second question is about the relative timing of temperature and carbon dioxide increases at the beginning of the last six interglacial periods.

The glacialinterglacial cycles of the last million years are in synch with periodic changes in Earth’s tilt and orbit that in turn control the amount and latitude of solar energy reaching us.

Increases in solar energy alone are only sufficient to warm the ocean a bit, but that is enough to release dissolved carbon dioxide (think warm soda) to the atmosphere where it drives further warming.

Ice cores from Antarctica and Greenland provide evidence that most of the temperature rise during an interglacial follows the increase in atmospheric carbon dioxide.

Mike Palin Dept of Geology, University of Otago