Our Changing World
Thursday 26 November 2015, with Alison Ballance & Veronika Meduna
On This Programme
- Antarctic glacier's past rapid retreat
- 'This issue will define my generation'
- Tea bag science
- Life at the edge
- Limiting nitrate leaching on dairy farms
Antarctic glacier's past rapid retreat
Research by New Zealand geoscientists, published overnight in the journal Nature Communications, reveals that Antarctic glaciers have retreated rapidly in the past, and that all it took was a minor climate warming.
A team led by Richard Jones, a postdoctoral research fellow at Victoria University, collected and analysed rocks from different elevations along the Mackay Glacier, which drains the massive East Antarctic Ice Sheet (EAIS).
The EAIS has long been thought more stable than the West Antarctic Ice Sheet, where the melting of several glaciers has now reached the point of no return, according to a NASA study published last year. This research adds evidence that the EAIS is not a sleeping giant, but has in the past responded quickly to warming.
Dr Jones says the chemical analysis of the rocks the team collected shows the Mackay Glacier retreated and thinned rapidly about 7000 years ago, and the retreat continued for several centuries.
He says the rate of retreat was similar to that seen today in glaciers in West Antarctica, where satellite observations show the ice sheet is thinning in response to a warming ocean, and losing more than 150 cubic kilometres of ice each year.
Quite a few of the outlet glaciers of the Antarctic ice sheet are thinning rapidly and are theorised to undergo massive changes in ice loss.
Associate professor Andrew Mackintosh, who is part of the research team, says the results provide the first geological evidence for the potential of runaway ice loss in Antarctica, triggered by what scientists describe as marine ice sheet instability.
“Before Richard’s study, we had theory about how ice sheets might respond and we had computer models that encapsulate this theory, but we had no direct geological evidence that this had occurred in the past.
"This gives us an example of how this can occur, the period of time that this might extend over, and the rate at which the ice might be lost."
Listen to Dr Mackintosh on Morning Report ( 3 min 39 sec )
The concept of marine ice sheet instability describes how parts of Antarctica’s ice sheet grounded below sea level will react to warming.
Dr Mackintosh says when most people think about glaciers, they think they sit on top of a mountain range. While that is true in many cases, he says large ice sheets can flow into deep troughs where the underlying rock lies below sea level.
“As ice sheets grow, they coalesce and thicken and invade the land that sits below sea level. They displace the sea. But that means that they have a vulnerability when they start to retreat. That area that used to be the ocean is then exposed again."
As a glacier begins to retreat backwards, thicker parts of ice flow with greater stress, and that can lead to a runaway feedback loop. “A little bit of ice retreat leads to much greater rates of ice loss.”
Dr Jones says the team chose the Mackay Glacier because of the morphology of the underlying rock.
There is a similar trough downstream of the Mackay Glacier. So the theory was that this glacier retreated in the past and must have experienced a similar thinning, but we didn’t know about the response time. This study is important in recognising the fact that this occurred and persisted for several hundred years.”
He says the trigger that set off the rapid retreat could have been minor. “Just a couple of years of warmer ocean temperatures would have been enough to initiate the retreat of that particular glacier, but then once it encountered this deep trough, that would have accelerated the ice loss.”
Dr Mackintosh says the findings came as a surprise.
“We went down there to understand the retreat of the ice sheet since the Last Glacial Maximum, when the ice sheet was larger than present, about 20,000 years ago. We know there’s an ice sheet there today … and that it was bigger in the past and we were trying to find out when that change occurred.
What Richard found is really dramatic. Most of this change occurred in one event that lasted for just a few hundred years and that occurred about 7000 years ago.
Ice core research has shown the climate in Antarctica returned to something similar to today’s climate about 12,000 years ago, as the world was emerging from the ice age, he says.
“The warming that occurred at the end of that last ice age was the trigger of the massive retreat of the ice sheet, and at a certain point the Mackay Glacier became independent of that large ice sheet and then underwent its own rapid transformation about 7000 years ago.”
The team will return to Antarctica in January to study a much larger glacier, which also drains the East Antarctic Ice Sheet, to look at its past thinning history.
The research was published in the journal Nature Communications.
'This issue will define my generation'
Concerned but undeterred.
That is how Lisa McLaren described her state of mind a day before she left for Paris this week to attend a youth climate conference in the lead-up to the UN climate talks.
Lisa is part of the nine-strong New Zealand Youth Delegation – all people in their 20s who have been selected to represent New Zealand and to advocate for a fair and liveable world for their generation.
In Paris, they will join thousands of other young people from countries throughout the world calling for stronger action on climate change.
Lisa says the group has discussed the recent attacks in Paris but everybody was determined to go anyway because the issue was too important.
This is something that will impact everyday New Zealanders, whether it will be through higher cost of importing products or issues around climate migrants. This will impact everybody.
Francisco Hernandez says the group wants to influence policy development and “expose the lack of action behind the rhetoric about a clean green New Zealand”.
“I am from the Philippines originally and have seen the impact of climate change on my hometown. These sort of climate-related disasters are going to get worse as climate change accelerates and I think that young people have a responsibility to do what we can to limit the damage and to future-proof our economies and societies.”
James Young-Drew says climate change defines his generation.
“It’s a global problem which touches all aspects of our lives. There will be economic consequences, there are moral components, human rights aspects. It touches on inter-generational equity and issues of social justice and because I’m in a position of relative privilege I want to do everything in my power to try and avoid these outcomes."
After the youth conference, the New Zealand team will observe during COP21, the 21st Conference of Parties (COP) to the UN Framework Convention on Climate Change, and report back to youth groups back home.
The COP21 meeting in Paris is expected to produce a legally binding agreement that commits countries to reducing their greenhouse gas emissions. The UN’s climate chief, Christiana Figueres, told Our Changing World in an earlier interview that a two-degree warming limit is an important goal, but that the pledges countries have submitted fall rather short of it.
Francisco Hernandez says on current pledges, the world is headed for 2.7 to 3.5 degrees of warming.
We can do better and get to a target below 2 degrees, but if no-one was working in the climate space and people didn’t see this as an issues, we would be headed to above 4 degrees.
Earlier this month, meteorologists at the UK's Met Hadley Centre have revealed that the rise in global mean temperature at the Earth's surface is set to reach 1 degree Celsius above pre-industrial levels for the first time.
New Zealand's target is to reduce greenhouse gas emissions to 11 per cent below 1990 levels by 2030.
Whatever the specific outcome of the Paris talks, the team says they are optimistic that it will set a course towards a decarbonised world.
Tea bag science
Tea bags. Most of us use them to make a cup of tea, But not Landcare Research ecologist Barbara Anderson. This avowed coffee drinker sees them as an indispensable bit of scientific kit.
“They’re really expensive tea bags, as far as tea bags go, but as far as scientific equipment goes they’re really cheap.”
And these are not just any old tea bags. They are a particular brand that isn’t sold in New Zealand, and Barbara and husband Ralf Ohlemüller, who collaborates on this research, had to ask various friends and family members to send them boxes of tea bags from overseas. This was quite a big ask as the team used 810 tea bags in their field experiments, with more required for use as controls.
Barbara says the Lipton tea bags really just standardised litter bags, filled with a known quantity of tea that has already been analysed by the Netherlands team that came up with the Tea Bag Index. The advantage of these particular tea bags is the synthetic bag, which doesn’t rot when it is buried in the ground.
“You weigh them, put them in the ground, and leave them for three months. The green and red tea leaves decompose at different rates, and that means you can use the different rates to find out the organic matter – or tea leaves in this case – that decomposes versus that which will stay in the ground as carbon.”
The research team is looking at how much carbon is in the soil system, and whether it’s acting as a carbon sink (storing carbon) or a carbon source (producing carbon).
Ralf, who is in the Department of Geography at the University of Otago says that “once we can quantify how climate drives whether a system is a carbon source or a carbon sink, we can then make a model of how climate or climate change impacts on these ecosystem properties.”
The study site is Barbara’s family’s farm in the Cardrona valley near Wanaka. The team were interested in how rates of decomposition vary with altitude and exposure, and they chose a prominent ridge on Mt Cardrona stretching from the peak at 1936 metres to the valley floor at 500 metres. Pairs of red and green tea bags were buried 10 centimetres deep each 100 metres. They were buried in January and pulled out in April, so were in the ground for summer. Temperature and soil moisture data were collected for every site.
When the team went to collect the tea bags at the end of April they had to battle an early fall of snow, which made finding and retrieving all the bags very challenging. “We had to chip them out of the ice” says Master’s student Robbert McCann.
“Basically we want to get a whole lot of information at one site across an elevation and an aspect gradient to look at the effect of microclimate” says Barbara.
“We really need to look at fine-scale studies if we want to say where climate changes and how it changes, and how it affects all species in mountainous environments” adds Ralf.
Ralf says that the weather information they have collected over two years is an exceptional record of climate across an altitudinal gradient, as it is difficult to collect this kind of information in mountain environments. It has given them precise figures around how much colder it is at high altitudes or on shady slopes, compared to lower or sunnier sites.
“There is a lot of research going at the moment about species living in mountainous species and what happens to these species – to plants and insects – under changing climates,” says Ralf. “And clearly, as it warms, these species will have to move up the mountain to track the climate that they need or like. And on lots of mountains they’ll simply run out of space. But what this sort of research shows is that maybe the species don’t actually have to move up the mountains – maybe they just have to go around the sides.”
This study is part of a wider research project into tussock grasslands and alpine regions, which Ralf says are very important for the water cycle and for endemic species,
Barbara was awarded a Rutherford Discovery Fellowship in 2012, which provides funding for 5 years. The tea bag study is part of Robbert McCann’s research for a Master’s degree.
The results of the New Zealand tea bag research will eventually be compared with other similar studies around the world, all carried out using identical tea bags and following the Tea Bag Index.
Life at the edge
On land, Antarctica is almost monochromatic. But just below the sea ice that surrounds the continent, the ocean floor teems with life and colour.
Sponges, corals, starfish, tube worms, shellfish, sea urchins and metre-long carnivorous nemertean worms all manage to forge a living in super-cooled water temperatures, with fluctuating food supplies and extremes in light conditions.
Light is crucial for life, but off the Antarctic coast, marine creatures have to get by without it for weeks during the long polar winter.
NIWA marine ecologist Vonda Cummings studies these Antarctic seafloor ecosystems.
She says despite these challenging conditions, invertebrate marine life around Antarctica is diverse. Many species are similar to those one would find in more temperate coastal waters, but some major groups, like crabs for example, are missing completely. Others flourish in numbers not seen in warmer waters.
Ice determines life under water. Only less than 1 per cent of the light that reaches the surface of the ice passes through it, cultivating patches of algae on the underside.
These algae are the ocean’s primary producers and the first link in the food web, but with the stark contrast in light between the Antarctic seasons, such food supplies fluctuate from feast to famine.
Vonda Cummings says bottom-dwelling creatures are well adapted to their dim and cold environment.
”A lot of them feed in multiple different ways. They might be filter feeders, scavengers or predators, so they are really good opportunistic feeders. They just take what they can get.”
But she says their finely tuned lifestyle at the edge means that they cope less well with gradual changes, such as warming seas and ocean acidification.
“The major thing is that these organisms have adapted to living within a certain range of temperatures. We are expecting massive - massive on their scale - changes over their lifetime. While a one or two degree increase in temperature might not seem much to us, when those guys are used to living within a one-to-two degree temperature range, that might just take them out of their tolerance envelope.”
Vonda Cummings is one of the speakers in the Royal Society of New Zealand’s Luminaries lecture series and will present her talk in Christchurch on Thursday 26. You can also watch the live-stream.
Limiting nitrate leaching on dairy farms
Nitrate leaching is a significant environmental issue, particularly on dairy farms, but soil scientists at Massey University are investigating how taking cows off pasture during certain periods of the year could reduce the problem, while potentially even increasing production.
When cows graze on a paddock, they deposit a patch of concentrated nitrogen every time they pee. From there, it can leach through the soil and pollute groundwater and streams.
At Massey University’s research dairy farm, Mike Hedley and his team are using a barn to take cows off pasture during certain times of the day to reduce nitrate leaching.
“A cow only takes about four hours to eat its grass and it doesn’t need to be in the paddock all the while between morning and evening milking and it can drop its urine somewhere else rather than in the field. It is those urine patches that cause most of the nitrate leaching.”
The project is part of Pastoral 21, a series of trials run in collaboration between the dairy industry and researchers to increase productivity while decreasing the environmental footprint of dairy farming.
The Massey University team is comparing traditional pasture grazing with farm management practices that either house cows part-time in a barn or take the herd off pasture in winter or on wet days.
In soil pits throughout the pasture, the team collects water samples after heavy rainfall to monitor the concentrations of nitrate, potassium, calcium and phosphate. Water is also collected from surface run-off plots to measure phosphate lost from the surface of the soil during a storm event.
Another aspect of the research is to monitor the impact of treading damage, or pugging, on pasture growth. James Hanly says the team developed a ‘puggometer’ to measure the relationship between soil moisture, treading damage and grass growth and to work out a protocol when cows would best be taken off pasture.
During the periods of housing, any effluent is collected in a pond and can be applied back to the paddock more evenly, either by spraying or injecting it into the soil at times when the soil is just dry and warm enough to avoid any drainage and nitrate leaching.
Mike Hedley says earlier trials have shown that on-off grazing practices can cut nitrate leaching by half, but even if housing is used only during autumn, it still reduces the problem by 38 per cent.
“Taking this from here to the farm-scale is the next step. Farmers could use the pugging score to recognise when they should take cows off the paddock. In terms of choosing the time of year when to put the cows into the house or stand them off, we recognise that if a farmer did that all year round it’s an awful lot of extra work. But if you focus on the autumn and summer period, certainly in the North Island and on non-irrigated farms, it fits much better into that part of the year.”
Even though the practice mitigates the problem of nitrate leaching, he says it remains to be seen if it can also increase production.