Earth's climate warmed more during the last 30 years of the 20th century than it did during any other three-decade period in the past 1,400 years. That's the finding of a new study by more than 80 scientists from 24 nations, who conclude that the modern-day temperature increase was driven by rising emissions of carbon dioxide and other so-called greenhouse gases.
The international research team reconstructed regional temperature shifts on all seven continents by analyzing climate data from tree rings, pollen, cave formations, ice cores, lake and ocean sediments, and historical records from around the world.
The most consistent trend over the past two millennia was decades-long periods of cooling, likely caused by a rise in volcanic activity, a decrease in solar radiation, changes in ground cover vegetation and slow variations in Earth's orbit around the sun. But the data show that with the exception of Antarctica, that natural cooling tapered off at the end of the 19th century, coinciding with the onset of industrialization and the resulting increase in greenhouse gas emissions.
The study, published in the journal Nature Geoscience, reveals that periods of warming and cooling might not have been global, with distinctive differences in average temperatures between the northern and southern hemispheres.
The new research data will be made public and incorporated into the next climate report by the United Nations-sponsored Intergovernmental Panel on Climate Change.