Penguins and sea lions beat a retreat to NZ during the Little Ice Age: Otago research
Penguins and sea lions beat a retreat to mainland New Zealand during the 500-year Little Ice Age, researchers say.
A University of Otago team has discovered the centuries-long cold spell caused shifts in wildlife habitats in the Southern Hemisphere.
The climate variation lasted from around 1300 until the mid-19th century.
Glaciers advanced, sea ice expanded, and the world endured freezing winters.
Explanations for climate cooling between the 14th and 19th century included reduced solar activity, volcanic eruptions, and changes in land use.
The Otago team used DNA and carbon dating on archaeological evidence, sub Antarctic island coastal midden remains, and ancient climate signatures.
University of Otago zoology professor Jon Waters said there was a clear pattern as cold-adapted sub Antarctic penguins and sea lions "suddenly moved north to mainland New Zealand, right at the start of the Little Ice Age, around 1500AD."
Polynesian settlers to the islands hunted species such as moa, penguins, and sea lions, he said.
When the temperature dropped, humans were inclined to move north, easing the hunting pressure while hunting reduced the local populations of wildlife. Into to this favourable environment, species such as the yellow-eyed penguin moved northwards.
"These species on Auckland Island and Campbell came up here in an interesting combination of [reduced] human pressure and climate. Species had been wiped out and left a niche. Then it turned cold making it unpleasant for the humans down south."
In other recent work, research showed humans hunted other species to extinction, including the Chatham sea lion, which was rapidly hunted to extinction in the 17th century.
"One distinctive feature of our spectacular wildlife is how many species have arrived here only over recent centuries.
"This new research points to the role of climate change in redistributing species as conditions shift across the planet," Waters said.
The drop in average Southern Hemisphere temperatures 500 years ago corresponds with the arrival of these species to New Zealand - the yellow-eyed penguin and the New Zealand sea lion - and occurred around 50 years to a century after the climate variation led to a dip in temperatures in the Northern Hemisphere.
In New Zealand, the cold helped to arrest human-driven hunting of mainland wildlife, particularly in the South Island, as Maori populations decreased in southern New Zealand.
DNA researcher Dr Nic Rawlence said the cold snap created opportunities for new species.
The findings were published in the international Journal of Biogeography.
In recent research by the Royal Astronomical Society, Professor Mike Lockwood said commentators frequently referred to the Little Ice Age in discussions of climate change but this was misleading as the temperature change was on a small scale - half a degree to 1C.
Paintings and literature from Europe and North America depict frozen lakes and rivers and heavy snow, but climatologists have struggled to explain the causes of the global variation.
The research suggested the era may need to be re-evaluated, as some parts of the world experienced drought and an increase in temperatures. The temperature difference during the 500-year period was about half a degree less than the average temperature, compared to the full-scale Ice Age 12,000 years ago, when global temperatures dipped by 8degC.
The concept of a 500-year ice age was misleading, the RAS said, as the variations were small scale compared to current climate change.
"On the whole the Little Ice Age was a manageable downturn in climate concentrated in particular regions, even though places like the UK had a larger fraction of cold winters. Our research suggests that there is no single explanation for this, that warm summers continued much as they do today and that not all winters were cold.
"This study provides little solace for the future, as we face the challenge of global warming. Solar activity appears to be declining at present, but any cooling effect that results will be more than offset by the effect of rising carbon dioxide emissions, and provides us with no excuse for inaction."