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.
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 findings show that 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.
The study, published in Nature GeoScience, was supported by the Natural Environment Research Council.
Dr Andrew Schurer, of the University of Edinburgh's School of GeoSciences, said: "Until now, the influence of the sun on past climate has been poorly understood. 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. Links between the sun and anomalously cold winters in the UK are still being explored."
NASA/JPL-Caltech via AFP/Getty Images
The heliopause is the point where solar winds stop and magnetic fields shift from the solar system to that of deep space."The latest data indicate that we are clearly in a new region where things are changing more quickly," Stone says.Voyager 1 and its identical sister ship, Voyager 2, also launched in 1977, between them explored all of the solar system's outer planets of Jupiter, Saturn, Uranus and Neptune in the 1980s.Back in 2004, the spacecraft crossed a boundary called the "termination shock," where the solar winds slow as they first meet interstellar space, which some scientists thought was the edge of the solar system.Where exactly the solar system "ends" is an ongoing debate among scientists. Voyager provides answers as it traverses this unexplored region."The most surprising thing about the outer limits of the solar system is how dynamic it is," Christian says. "Even though the outer solar system is an extremely good vacuum, there is still a lot going on. We're going where no one has been before."Both Voyagers continue to make unexpected discoveries about the physical structure of the solar system."We've been surprised by Voyager again and again," Christian says. "I actually think that the Voyager mission is one of NASA's best success stories. That both Voyagers are still working well, nearly 35 years after launch, and sending back important science from 10 billion miles away is truly amazing."In about 200,000 years or so, one of the craft might come close to another star, Christian says.Though they will lose the power to transmit data back to Earth sometime between 2020 or 2025, both will continue their journey into deep space."The spacecraft will go on forever," Stone says.For more information about reprints & permissions, visit our FAQ's. To report corrections and clarifications, contact Standards Editor Brent Jones. For publication consideration in the newspaper, send comments to letters@usatoday.com. Include name, phone number, city and state for verification. To view our corrections, go to corrections.usatoday.com.