Greenhouse gases, not Sun, key driver of climate change

Variations in heat from the Sun have not strongly influenced climate change, a new study shows, contradicting the belief that long warm and cold periods in the Earth's dynamic past were caused by solar activity.
Research examining the causes of climate change in the northern hemisphere over the past 1000 years has shown that until the year 1800, the key driver of periodic changes in climate was volcanic eruptions.
These tend to prevent sunlight reaching Earth, causing cool, drier weather. Since 1900, greenhouse gases have been the primary cause of climate change, the research found.
The findings overturn a widely held scientific view that lengthy periods of warm and cold weather in the past might have been caused by periodic fluctuations in solar activity.

They show periods of low Sun activity should not be expected to have a large impact on temperatures on Earth, and are expected to improve scientists' understanding and help climate forecasting.
Scientists at the University of Edinburgh carried out the study using records of past temperatures constructed with data from tree rings and other historical sources.

They compared this data record with computer-based models of past climate, featuring both significant and minor changes in the Sun.
They found that their model of weak changes in the Sun gave the best correlation with temperature records, indicating that solar activity has had a minimal impact on temperature in the past millennium.

"Until now, the influence of the Sun on past climate has been poorly understood," Dr Andrew Schurer, of the University of Edinburgh's School of GeoSciences, said.
"We hope that our new discoveries will help improve our understanding of how temperatures have changed over the past few centuries, and improve predictions for how they might develop in future," said Schurer.
The study was published in the journal Nature GeoScience.