April 24, 2013 — A massive study of temperature changes on Earth's continents over the past 1,000 to 2,000 years suggests that a long-term cooling trend ended in the late 19th century, and human activity is the likely cause.
A long-term global cooling trend was 'reversed' by a surge in greenhouse gases in the 20th century, a new study suggests.
A consortium of 78 authors from 24 countries participated in the report.
Researchers used a massive sampling of publicly-available data to track the Earth's temperature across the continents over the past 1,000 to 2,000 years.
The study suggests that the 20th century is either the warmest or among the warmest on record across all continents, with the exception of Antarctica as well as Africa, which could not provide sufficient data to participate in the analysis.
Global cooling trends are caused by natural factors and can trigger fluctuations in temperature and a rise in volcanic activity. The study's authors argue that greenhouse gases played a direct role in rising global temperatures.
"The new results show that climate change is, as usual, more complicated than we expected: long, millennial natural cooling trends were punctuated by warming episodes that turned out to be more local than we thought," said Paul E. Filmer, an author in the study, in a statement.
"The natural forces driving the cooling are still present today, but since the nineteenth century an additional, stronger, warming driver has been added: human activity. We cannot match the temperature records since then without factoring in this new driver."
More information on the study can be found on the PAGES Scientific Community website.