Andrew Schurer1, Simon F.B. Tett1,2, Gabriele Hegerl1,2
1University of Edinburgh, United Kingdom, 2NCAS-Climate
Dr. Andrew Schurer is a Research Associate at the University of Edinburgh specialising in the climate of the last millennium
What are the new findings?
We find that changes in temperature over the Northern Hemisphere (all regions north of the equator) over the last thousand years were not strongly influenced by variations in heat from the sun. Instead, volcanic eruptions seem to be the most important influence up until 1800, causing cooler drier weather by preventing sunlight from reaching the Earth. Since 1900, greenhouse gases have been the primary cause of climate change.
Why are these findings important?
The change in the amount of energy from the sun reaching the top of the Earth’s atmosphere is only well understood over the last few decades – the period covered by satellite observations. Solar scientists have long known that there might be larger longer term changes in the sun’s activity but cannot be certain how large these effects are likely to be. This study helps by assessing the effects of solar variability over the last millennium – in particular ruling out large variations in incoming energy from the sun. This will help improve our understanding of how temperatures have changed in the past, and improve predictions for how they might change in the future.
How did we discover this?
This study used records of past temperatures constructed using data from tree rings and other historical sources compared with computer-based simulations of past climate, featuring both large and small changes in solar activity. A statistical analysis was undertaken to determine what amount of expected change, as calculated by the models, was consistent with a wide range of possible temperature records.
Above: Observed changes in Northern hemisphere temperature (blue lines) compared to computer simulations with strong (green) and weak (red) solar variability. A statistical analysis rules out high solar variability.
Find out more:
- see Andrew Schurer's webpage
- Take a look at the Journal article
Schurer, A. P., S. F. B. Tett, and G. C. Hegerl (2013), Nat. Geo., DOI 10.1038/ngeo2040
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