Solar and volcanic forcing of the Southern Hemisphere climate over the past 1500 years

The past 1500 years provides a valuable opportunity to study the role of external forcings in driving the global climate. Significant changes have taken place within the climate system over this period, and proxy data that records these changes covers a wide geographical area and has high temporal resolution. Natural and anthropogenic forcings are also reasonably well constrained. While previous detection and attribution studies have found a significant role of volcanic eruptions in driving the pre-industrial Northern Hemisphere climate, the drivers of the Southern Hemisphere climate are much less well understood. Here, the CSIRO Mk3L climate system model is used to simulate the global climate of the past 1500 years. Different combinations of natural and anthropogenic forcings are applied, including changes in the Earth’s orbital parameters, solar irradiance, volcanic emissions and anthropogenic greenhouse gases. The simulations are then compared with a multi-proxy reconstruction of Southern Hemisphere temperature. We find strong solar and volcanic influences on the Southern Hemisphere climate during the pre-industrial period, with the anthropogenic signal becoming increasingly dominant after 1850 CE. However, the results are sensitive to the specific reconstructions of solar and volcanic activity that are used to drive the model. The choice of volcanic reconstruction is particularly critical, and we find that the dating of major eruptions can impact significantly upon the agreement between the model and the proxy record. If we are to learn all that we can from the climate of recent millennia, a critical challenge is therefore to develop better reconstructions of past climatic forcings − particularly volcanic eruptions.
Solar activity, Volcanic gases, Southern Hemisphere, Climates, Volcanoes, Geographical variations, Greenhouse gases
Phipps, S., Ackerley, D., Brown, J., Curran, M., Fischer, M., Gallant, A., Gergis, J., McGregor, H., Neukom, R., Plummer, C., Stevenson, S., & van Ommen, T. (2013). Solar and volcanic forcing of the Southern Hemisphere climate over the past 1500 years. Paper presented the Past Global Changes 4th Open Science Meeting, Goa, India 13-16 February 2013.