Record high to record low: what on earth is happening to Antarctica’s sea ice?

Nerilie Abram, Australian National University; Matthew England, UNSW Australia, and Tessa Vance, University of Tasmania

2016 continues to be a momentous year for Australia’s climate, on track to be the new hottest year on record.

To our south, Antarctica has also just broken a new climate record, with record low winter sea ice. After a peak of 18.5 million square kilometres in late August, sea ice began retreating about a month ahead of schedule and has been setting daily low records through most of September.

It may not seem unusual in a warming world to hear that Antarctica’s sea ice – the ice that forms each winter as the surface layer of the ocean freezes – is reducing. But this year’s record low comes hot on the heels of record high sea ice just two years ago. Overall, Antarctica’s sea ice has been growing, not shrinking.

So how should we interpret this apparent backflip? In our paper published today in Nature Climate Change we review the latest science on Antarctica’s climate, and why it seems so confusing.

Antarctica’s sea ice has reached a record low this year.
NASA, Author provided

Antarctic surprises

First up, Antarctic climate records are seriously short.

The International Geophysical Year in 1957/58 marked the start of many sustained scientific efforts in Antarctica, including regular weather readings at research bases. These bases are mostly found on the more accessible parts of Antarctica’s coast, and so the network – while incredibly valuable – leaves vast areas of the continent and surrounding oceans without any data.

In the end, it took the arrival of satellite monitoring in the 1979 to deliver surface climate information covering all of Antarctica and the Southern Ocean. What scientists have observed since has been surprising.

Overall, Antarctica’s sea ice zone has expanded. This is most notable in the Ross Sea, and has brought increasing challenges for ship-based access to Antarctica’s coastal research stations. Even with the record low in Antarctic sea ice this year, the overall trend since 1979 is still towards sea ice expansion.

The surface ocean around Antarctica has also mostly been cooling. This cooling masks a much more ominous change deeper down in the ocean, particularly near the West Antarctic Ice Sheet and the Totten glacier in East Antarctica. In these regions, worrying rates of subsurface ocean warming have been detected up against the base of ice sheets. There are real fears that subsurface melting could destabilise ice sheets, accelerating future global sea level rise.

In the atmosphere we see that some parts of the Antarctic Peninsula and West Antarctica are experiencing rapid warming, despite average Antarctic temperatures not changing that much yet.

In a rapidly warming world these Antarctic climate trends are – at face value – counterintuitive. They also go against many of our climate model simulations, which, for example, predict that Antarctica’s sea ice should be in decline.

Jan Lieser, Author provided

Winds of change

The problem we face in Antarctica is that the climate varies hugely from year to year, as typified by the enormous swing in Antarctica sea ice over the past two years.

This means 37 years of Antarctic surface measurements are simply not enough to detect the signal of human-caused climate change. Climate models tell us we may need to monitor Antarctica closely until 2100 before we can confidently identify the expected long-term decline of Antarctica’s sea ice.

In short, Antarctica’s climate remains a puzzle, and we are currently trying to see the picture with most of the pieces still missing.

But one piece of the puzzle is clear. Across all lines of evidence a picture of dramatically changing Southern Ocean westerly winds has emerged. Rising greenhouse gases and ozone depletion are forcing the westerlies closer to Antarctica, and robbing southern parts of Australia of vital winter rain.

The changing westerlies may also help explain the seemingly unusual changes happening elsewhere in Antarctica.

The expansion of sea ice, particularly in the Ross Sea, may be due to the strengthened westerlies pushing colder Antarctic surface water northwards. And stronger westerlies may isolate Antarctica from the warmer subtropics, inhibiting continent-scale warming. These plausible explanations remain difficult to prove with the records currently available to scientists.

Australia’s unique climate position

The combination of Antarctica’s dynamic climate system, its short observational records, and its potential to cause costly heatwaves, drought and sea-level rise in Australia, mean that we can’t afford to stifle fundamental research in our own backyard.

Our efforts to better understand, measure and predict Antarctic climate were threatened this year by funding cuts to Australia’s iconic climate research facilities at the CSIRO. CSIRO has provided the backbone of Australia’s Southern Ocean measurements. As our new paper shows, the job is far from done.

A recent move to close Macquarie Island research station to year-round personnel would also have seriously impacted the continuity of weather observations in a region where our records are still far too short. Thankfully, this decision has since been reversed.

But it isn’t all bad news. In 2016, the federal government announced new long-term funding in Antarctic logistics, arresting the persistent decline in funding of Antarctic and Southern Ocean research.

The nearly A$2 billion in new investment includes a new Australian icebreaking ship to replace the ageing Aurora Australis. This will bring a greater capacity for Southern Ocean research and the capability to push further into Antarctica’s sea ice zone.

Whatever the long-term trends in sea ice hold it is certain that the large year-to-year swings of Antarctica’s climate will continue to make this a challenging but critical environment for research.

The Conversation

Nerilie Abram, Senior Research Fellow, Research School of Earth Sciences; Associate Investigator for the ARC Centre of Excellence for Climate System Science, Australian National University; Matthew England, Australian Research Council Laureate Fellow; Deputy Director of the Climate Change Research Centre (CCRC); Chief Investigator in the ARC Centre of Excellence in Climate System Science, UNSW Australia, and Tessa Vance, Palaeoclimatologist, Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania

This article was originally published on The Conversation. Read the original article.


Putting carbon back in the land is just a smokescreen for real climate action: Climate Council report

Martin Rice and Will Steffen, Australian National University

Just as people pump greenhouse gases into the atmosphere by burning fossil fuels, the land also absorbs some of those emissions. Plants, as they grow, use carbon dioxide and store it within their bodies.

However, as the Climate Council’s latest report shows, Australia’s fossil fuels (including those burned overseas) are pumping 6.5 times as much carbon into the atmosphere as the land can absorb. This means that, while storing carbon on land is useful for combating climate change, it is no replacement for reducing fossil fuel emissions.

Land carbon is the biggest source of emission reductions in Australia’s climate policy centrepiece – the Emissions Reduction Fund. This is smoke and mirrors: a distraction from the real challenge of cutting fossil fuel emissions.

Land carbon

Land carbon is part of the active carbon cycle at the Earth’s surface. Carbon is continually exchanging between the land, ocean and atmosphere, primarily as carbon dioxide.

In contrast, carbon in fossil fuels has been locked away from the active carbon cycle for millions of years.

Carbon stored on land is vulnerable to being returned to the atmosphere. Natural disturbances such as bushfires, droughts, insect attacks and heatwaves, many of which are being made worse by climate change, can trigger the release of significant amounts of land carbon back to the atmosphere.

Changes in land management, as we’ve seen in Queensland, for example, with the relaxation of land-clearing laws by the previous state government, can also affect the capability of land systems to store carbon.

Burning fossil fuels and releasing CO₂ to the atmosphere thus introduces new and additional carbon into the land-atmosphere-ocean cycle. It does not simply redistribute existing carbon in the cycle.

The ocean and the land absorb some of this extra carbon. In fact, just over half of this additional carbon is removed from the atmosphere, and split roughly equally between the land and the ocean. However, this leaves almost half of the CO₂ emitted from fossil fuel combustion in the atmosphere. It’s this remaining CO₂ that is driving global warming.

Figure 2. Changes in the global carbon cycle from 1850 to 2014. Positive changes (above the horizontal zero line) show carbon added to the atmosphere and negative changes (below the line) show how this carbon is then distributed among the ocean, land and atmosphere.
Adapted from Le Quéré et al. 2015, data from CDIAC/NOAA-ESRL/GCP/Joos et al. 2013/Khatiwala et al. 2013.

Although Australia’s land sector has absorbed more carbon than it has emitted over the past decade or two, this has been overshadowed by our domestic fossil fuel emissions and those from our exported fossil fuels. These are roughly 6.5 times greater than the uptake of carbon by Australian landscapes.

Under international carbon accounting protocols, emissions are assigned to the country that burns the fossil fuels. However, many Australians are becoming increasing concerned about the ethics associated with exploiting our fossil fuels, no matter where they are burned.

In short, we’ve got a big problem that requires a global response, which includes a strong commitment from Australia.

Falling short of our commitment

Last December, Australia joined the rest of the world in pledging to do everything possible to limit global warming to no more than 2°C above pre-industrial levels, and furthermore to pursue efforts to limit the increase to 1.5°C. Yet Australia lacks a robust, credible long-term plan to cut Australia’s CO₂ emissions from fossil fuel combustion.

Current climate change policies and practices in Australia allow for the use of land carbon “offsets” – that is, carbon taken up by land systems can be used to offset or subtract from fossil fuel emissions. For example, the government’s Emissions Reduction Fund (ERF) provides financial incentives for organisations or individuals to adopt new practices or technologies that reduce or sequester greenhouse gas emissions.

Currently, vegetation (land system) projects represent the majority of ERF-accepted projects (185 out of 348). And yet, while storing carbon on land can be useful, it must be additional to, and not instead of, reducing fossil fuel emissions. Moreover, numerous critiques have questioned the effectiveness of the ERF.

Problems of scale

We also have a problem of scale. Reducing emissions through land carbon methods could save up to 38 billion tonnes of carbon globally by 2050 if combined with sustainable land management practices. By comparison, global carbon emissions from fossil fuel combustion are currently around 10 billion tonnes per year.

If this rate is continued, total fossil fuel emissions from 2015 to 2050 will be about 360 billion tonnes – nearly 10 times larger than the maximum estimated biological carbon sequestration of 38 billion tonnes over the same period.

It is now virtually certain that the carbon budget (the amount of carbon that can be produced while keeping warming below a certain level) will be exceeded. To meet the Paris 1.5°C aspirational target (and probably to meet the 2°C target) will require the use of negative emission technologies throughout the second half of the century.

However, no proposed negative emission technology has yet been proven to be feasible technologically at large scale and at reasonable cost, so this approach remains an in-principle option only. For effective climate action, the emphasis must remain on reducing emissions from fossil fuel combustion.

Using land carbon to “offset” our fossil fuel emissions is ultimately a smokescreen for real climate action.

Our thanks to Jacqui Fenwick for co-authoring this article and the report.

The Conversation

Martin Rice, Head of Research, The Climate Council of Australia and Honorary Associate, Department of Environmental Sciences and Will Steffen, Adjunct Professor, Fenner School of Environment and Society, Australian National University

This article was originally published on The Conversation. Read the original article.