Thursday, January 14, 2016
Global warming could stave off next ice age for 100,000 years
In the past million years, the world has had about 10 ice ages before swinging back to warmer conditions like the present.
In the last ice age that ended 12,000 years ago, ice sheets blanketed what is now Canada, northern Europe and Siberia.
In a new explanation for the long-lasting plunges in global temperatures that cause ice ages, scientists pointed to a combination of long-term shifts in the Earth's orbit around the sun, together with levels of carbon dioxide in the atmosphere.
They said the planet seemed naturally on track to escape an ice age for the next 50,000 years, an unusually long period of warmth, according to the study led by the Potsdam Institute for Climate Impact Research and published in the journal Nature.
But rising man-made greenhouse gas emissions since the Industrial Revolution began in the 18th century could mean the balmy period will last for 100,000 years.
The findings suggest human influences "will make the initiation of the next ice age impossible over a time period comparable to the duration of previous glacial cycles".
"Humans have the power to change the climate on geological timescales," lead author Dr Andrey Ganopolski said.
He said the lingering impacts of greenhouse gases in a far distant future did not in any way affect the urgency of cutting emissions now that are blamed for causing downpours, heat waves and rising seas.
"The earlier we stop, the better," Dr Ganopolski said.
Almost 200 governments agreed a deal in Paris last month to shift from fossil fuels to combat climate change.
Last week, another group of scientists said humanity had become a force in shaping the planet's geology and suggested an "Anthropocene epoch" began in the mid-20th century with factors such as nuclear tests and industrialisation.
"Like no other force on the planet, ice ages have shaped the global environment," co-author Professor Hans Joachim Schellnhuber said.
Professor Schellnhuber, director of the Potsdam Institute, suggested a new epoch might instead be called the "Deglacial".
Some past studies have suggested that global warming can delay ice ages, but the current study is more specific.
It indicates the start of past ice ages coincided with low levels of solar energy reaching the Earth in northern summers, like in current times. But an ice age had not begun because of relatively high, apparently natural, levels of carbon dioxide in the atmosphere since before the Industrial Revolution.
Ice age cycles caused by sun plus carbon dioxide
Ice age cycles are caused by regular cycles in the Earth's orbit, amplified by factors such as changes in ice coverage and carbon dioxide, the University of Reading's Professor Richard Allen explained.
"Earth's orbit around the sun is oval in shape but this becomes more circular every 100,000 years and more particularly so every 400,000 year," he said.
Professor Allen said the world was currently in a mild interlude coinciding with a near-circular orbit like one 400,000 years ago when the mild interglacial lasted longer than usual.
"We know that our current warm period will last many tens of thousands of years even without elevated concentrations of greenhouse gases associated with human activity," he said.
But the delay in the timing of an ice age is of less concern than the immediate impact of climate change, Professor Allen said.
"The many tens of thousands of years after which the next ice age may commence is very long compared to the appearance of modern human societies and is not worth worrying about compared to immediate concerns about damaging human-caused climate change expected over the coming decades if no action is takes to mitigate this likelihood," he said.