Ice ages are the outstanding mystery in Earth sciences

Today we’re speaking with climate scientist Peter Huybers of Harvard. Dr. Huybers received a 2009 genius grant from the MacArthur Foundation. He spoke with EarthSky about why ice ages ended 12,000 years ago.

Peter Huybers: I think ice ages are really the outstanding mystery in Earth sciences presently.

Scientists have scrutinized the evidence for ice ages in Earth’s past. Dr. Huyber’s recent research focused on one possible factor triggering the end of an ice age – volcanic activity.

Peter Huybers: The major finding was that there was a dramatic uptick in volcanic activity during the last deglaciation.

Volcanoes can cause carbon dioxide, or CO2 – a greenhouse gas – to increase in Earth’s atmosphere.
Twelve thousand years ago, volcanoes might have caused warming and melting ice. In some places on Earth, melting ice sheets might have taken a load off rock below. That might have increased volcanic activity even more – which means more CO2 – and more warming.

Peter Huybers: In so much as volcanoes played an important role in providing a feedback in past climate, we can then contrast that with the even much stronger control of CO2, which humans are exerting.

In other words, volcanoes at the end of the last ice age were releasing about three-tenths of a gigaton of CO2 each year. Today, humans are releasing about a hundred times more.

Dr. Huybers spoke of two things that are poorly understood about what cause ice sheets to begin to melt.

Peter Huybers: The first is what causes an ice sheet to go unstable, and how rapidly can an ice sheet then disintegrate. And the second thing is, what is it that causes atmospheric CO2 during these glacial cycles to go up and down such that we have less atmospheric CO2 when there’s a lot of ice, and vice-versa.

Dr. Huybers spoke more about his 2009 study which found increased volcanic activity at the end of Earth’s last ice age, around 12,000 years ago.

Peter Huybers: This is work I did with Charles Langmeir, what we were looking at, it’s really two parts. The first is, we were trying to understand, how has volcanic activity on a global scale changed over the last 40 thousand years. And what we did was, we took as many different radio carbon dates we could find of individual volcanic eruptions, and using statistical models, attempted to reconstruct what the frequency of volcanic events were, through time.

That’s when he and Langmeir found what they called “a dramatic uptick” in volcanic activity around the end of the last ice age.

Peter Huybers: Now, the second part of this study is really to ask, what are the implications of this increase in volcanism? Typically, people think of volcanoes throwing a lot of aerosols and other things up into the atmosphere that blocks sunlight and leads to a cooling. That’s definitely true on a short term effect. But what we were thinking about really was, what’s the long-term implications. If you have increased vulcanism, ongoing for 10,000 years, what does that do, in particular, to the carbon budget?

These scientists then extrapolated modern rates of volcanic emissions – which are about 0.1 gigatons of CO2 per year – back into the time period from 20,000 to 10,000 years ago.

Peter Huybers: This is where we see approximately three times increase in global volcanic activity. And if we have a sustained, ongoing increase in volcanic activity, the implications are that we would expect this to increase atmospheric CO2 and perhaps account for as much as half of the increase in atmospheric CO2, which we’ve seen coming out of the last deglaciation. So this is about 50 parts per million in the atmosphere.

There are two parts to the scientific evidence in the study, said Huybers.

Peter Huybers: It’s really these two different lines of evidence, one from dating of direct volcanic material, and another from the ice core evidence lining up together, that that gives us some confidence that this is a real event that really was ongoing through the deglaciation in a global fashion.

Huybers summed up some important points to takeaway from the study.

Peter Huybers: What our study tries to do is understand the inter-relationship of changes in ice loading atop the continents, how that decrease in ice loading could increase volcanic activity, and how that increase in volcanic activity may be in part responsible for the increase in atmospheric CO2 which is observed as we come out of the last glacial.