Earth’s natural cycles can’t account for the recent warming seen over the past 100 years, new research suggests.In one of three new studies published in the journals Nature and Nature Geoscience, researchers found that previous periods of climate change such as the Little Ice Age and the Medieval Warming Period were regional and not a global phenomenon.
In contrast, the warming that has occurred over the past century has been far-reaching and global in nature.”In this paper, what we do is look at climate over the past 2,000 years — and traditionally the understanding of climate over this period is that there were globally coherent periods of climate variability,” said Nathan Steiger, co-author of the paper and an associate researcher at the Lamont-Doherty Earth Observatory at Columbia University. “But what we show is that these periods are not globally coherent, as previously thought.”
In order to obtain a robust sampling of data around the world, the researchers used 700 records obtained from trees, ice, coral, sediment and more.In the case of the Little Ice Age, the researchers found that different parts of the planet experienced changes at different times.
The central and eastern Pacific regions experienced their coldest temperatures in 2,000 years during the 15th century. But in northwestern Europe and southeastern North America, the coldest temperatures occurred during the 17th century. For everywhere else, it occurred during the 19th century.
In contrast, the warming we are seeing today spans 98 per cent of the planet.Their study only went as far as the year 2000, but nine of the 10 warmest years on record have occurred since then, with the past five years being the warmest.
Those who question or disagree with scientific evidence pointing to anthropogenic, or human-caused, climate change often cite Earth’s natural cycles as one of the reasons for the planet’s recent warming. The Little Ice Age is most often presented as evidence of part of this natural cycle.But, Steiger said, “internal variability [doesn’t] explain the coherence that we see for the contemporary warming.”