Contributions to sea-level rise have increased by half since 1993, largely because of Greenland’s ice



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Water mass enters the ocean from glaciers such as this along the Greenland coast.
NASA/JPL-Caltech

John Church, UNSW; Christopher Watson, University of Tasmania; Matt King, University of Tasmania; Xianyao Chen, and Xuebin Zhang, CSIRO

Contributions to the rate of global sea-level rise increased by about half between 1993 and 2014, with much of the increase due to an increased contribution from Greenland’s ice, according to our new research.

Our study, published in Nature Climate Change, shows that the sum of contributions increased from 2.2mm per year to 3.3mm per year. This is consistent with, although a little larger than, the observed increase in the rate of rise estimated from satellite observations.

Globally, the rate of sea-level rise has been increasing since the 19th century. As a result, the rate during the 20th century was significantly greater than during previous millennia. The rate of rise over the past two decades has been larger still.

The rate is projected to increase still further during the 21st century unless human greenhouse emissions can be significantly curbed.

However, since 1993, when high-quality satellite data collection started, most previous studies have not reported an increase in the rate of rise, despite many results pointing towards growing contributions to sea level from the ice sheets of Greenland and Antarctica. Our research was partly aimed at explaining how these apparently contradictory results fit together.

Changes in the rate of rise

In 2015, we completed a careful comparison of satellite and coastal measurements of sea level. This revealed a small but significant bias in the first decade of the satellite record which, after its removal, resulted in a slightly lower estimate of sea-level rise at the start of the satellite record. Correcting for this bias partially resolved the apparent contradiction.

In our new research, we compared the satellite data from 1993 to 2014 with what we know has been contributing to sea level over the same period. These contributions come from ocean expansion due to ocean warming, the net loss of land-based ice from glaciers and ice sheets, and changes in the amount of water stored on land.

Previously, after around 2003, the agreement between the sum of the observed contributions and measured sea level was very good. Before that, however, the budget didn’t quite balance.

Using the satellite data corrected for the small biases identified in our earlier study, we found agreement with the sum of contributions over the entire time from 1993 to 2014. Both show an increase in the rate of sea-level rise over this period.

The total observed sea-level rise is the sum of contributions from thermal expansion of the oceans, fresh water input from glaciers and ice sheets, and changes in water storage on land.
IPCC

After accounting for year-to-year fluctuations caused by phenomena such as El Niño, our corrected satellite record indicates an increase in the rate of rise, from 2.4mm per year in 1993 to 2.9mm per year in 2014. If we used different estimates for vertical land motion to estimate the biases in the satellite record, the rates were about 0.4mm per year larger, changing from 2.8mm per year to 3.2mm per year over the same period.

Is the whole the same as the sum of the parts?

Our results show that the largest contribution to sea-level rise – about 1mm per year – comes from the ocean expanding as it warms. This rate of increase stayed fairly constant over the time period.

The second-largest contribution was from mountain glaciers, and increased slightly from 0.6mm per year to 0.9mm per year from 1993 to 2014. Similarly, the contribution from the Antarctic ice sheet increased slightly, from 0.2mm per year to 0.3mm per year.

Strikingly, the largest increase came from the Greenland ice sheet, as a result of both increased surface melting and increased flow of ice into the ocean. Greenland’s contribution increased from about 0.1mm per year (about 5% of the total rise in 1993) to 0.85mm per year (about 25% in 2014).

Greenland’s contribution to sea-level rise is increasing due to both increased surface melting and flow of ice into the ocean.
NASA/John Sonntag, CC BY

The contribution from land water also increased, from 0.1mm per year to 0.25mm per year. The amount of water stored on land varies a lot from year to year, because of changes in rainfall and drought patterns, for instance. Despite this, rates of groundwater depletion grew whereas storage of water in reservoirs was relatively steady, with the net effect being an increase between 1993 and 2014.

So in terms of the overall picture, while the rate of ocean thermal expansion has remained steady since 1993, the contributions from glaciers and ice sheets have increased markedly, from about half of the total rise in 1993 to about 70% of the rise in 2014. This is primarily due to Greenland’s increasing contribution.

What is the future of sea level?

The satellite record of sea level still spans only a few decades, and ongoing observations will be needed to understand the longer-term significance of our results. Our results also highlight the importance of the continued international effort to better understand and correct for the small biases we identified in the satellite data in our earlier study.

Nevertheless, the satellite data are now consistent with the historical observations and also with projected increases in the rate of sea-level rise.

Ocean heat content fell following the 1991 volcanic eruption of Mount Pinatubo. The subsequent recovery (over about two decades) probably resulted in a rate of ocean thermal expansion larger than from greenhouse gases alone. Thus the underlying acceleration of thermal expansion from human-induced warming may emerge over the next decade or so. And there are potentially even larger future contributions from the ice sheets of Greenland and Antarctica.

The ConversationThe acceleration of sea level, now measured with greater accuracy, highlights the importance and urgency of cutting greenhouse gas emissions and formulating coastal adaptation plans. Given the increased contributions from ice sheets, and the implications for future sea-level rise, our coastal cities need to prepare for rising sea levels.

Sea-level rise will have significant impacts on coastal communities and environments.
Bruce Miller/CSIRO, CC BY

John Church, Chair professor, UNSW; Christopher Watson, Senior Lecturer, Surveying and Spatial Sciences, School of Land and Food, University of Tasmania; Matt King, Professor, Surveying & Spatial Sciences, School of Land and Food, University of Tasmania; Xianyao Chen, Professor, and Xuebin Zhang, Senior research scientist, CSIRO

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

Volcanoes under the ice: melting Antarctic ice could fight climate change



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Furious winds keep the McMurdo Dry Valleys in Anarctica free of snow and ice. Calcites found in the valleys have revealed the secrets of ancient subglacial volcanoes.
Stuart Rankin/Flickr, CC BY-NC

Silvia Frisia, University of Newcastle

Iron is not commonly famous for its role as a micronutrient for tiny organisms dwelling in the cold waters of polar oceans. But iron feeds plankton, which in turn hold carbon dioxide in their bodies. When they die, the creatures sink to the bottom of the sea, safely storing that carbon.

How exactly the iron gets to the Southern Ocean is hotly debated, but we do know that during the last ice age huge amounts of carbon were stored at the bottom of the Southern Ocean. Understanding how carbon comes to be stored in the depth of the oceans could help abate CO2 in the atmosphere, and Antarctica has a powerful role.

Icebergs and atmospheric dust are believed to have been the major sources of this micronutrient in the past. However, in research published in Nature Communications, my colleagues and I examined calcite crusts from Antarctica, and found that volcanoes under its glaciers were vital in delivering iron to the ocean during the last ice age.

Today, glacial meltwaters from Greenland and the Antarctic peninsula supply iron both in solution and as tiny particles (less than 0.0001mm in diameter), which are readily consumed by plankton. Where glaciers meet bedrock, minute organisms can live in pockets of relatively warm water. They are able to extract “food” from the rock, and in doing so release iron, which then can be carried by underwater rivers to the sea.

Volcanic eruptions under the ice can create underwater subglacial lakes, which, at times, discharge downstream large masses of water that travel to the ice margin and beyond, carrying with them iron in particle and in solution.

The role of melting ice in climate change is as yet poorly understood. It’s particularly pertinent as scientists predict the imminent collapse of part of the Larsen C ice shelf.

Researchers are also investigating how to reproduce natural iron fertilisation in the Southern Ocean and induce algal blooms. By interrogating the volcanic archive, we learn more about the effect that iron fertilisation from meltwater has on global temperatures.

A polished wafer of the subglacial calcites. The translucent, crystalline layers formed while in pockets of water, providing nourishment to microbes. The opaque calcite with rock fragments documents a period when waters discharged from a subglacial lake formed by a volcanic eruption, carrying away both iron in solution and particles of iron.
Supplied

The Last Glacial Maximum

During the Last Glacial Maximum, a period 27,000 to 17,000 years ago when glaciers were at their greatest extent worldwide, the amount of CO2 in the atmosphere was lowered to 180 parts per million (ppm) relative to pre-industrial levels (280 ppm).

Today we are at 400 ppm and, if current warming trends continue, a point of no return will be reached. The global temperature system will return to the age of the dinosaurs, when there was little difference in temperature from the equator to the poles.

If we are interested in providing a habitable planet for our descendants, we need to mitigate the quantity of carbon in the atmosphere. Blooms of plankton in the Southern Ocean boosted by iron fertilisation were one important ingredient in lowering CO2 in the Last Glacial Maximum, and they could help us today.

The Last Glacial Maximum had winds that spread dust from deserts and icebergs carrying small particles into the Southern Ocean, providing the necessary iron for algal blooms. These extreme conditions don’t exist today.

Hidden volcanoes

Neither dust nor icebergs alone, however, explain bursts of productivity recorded in ocean sediments in the Last Glacial Maximum. There was another ingredient, only discovered in rare archives of subglacial processes that could be precisely dated to the Last Glacial Maximum.

Loss of ice in Antartica’s Dry Valleys uncovered rusty-red crusts of calcite plastered on glacially polished rocks. The calcites have tiny layers that can be precisely dated by radiometric techniques.

A piece of subglacial calcite coating pebbles. This suggests that the current transporting the pebbles was quite fast, like a mountain stream. The pebbles were deposited at the same time as the opaque layer in the calcite formed.
Supplied

Each layer preserves in its chemistry and DNA a record of processes that contributed to delivering iron to the Southern Ocean. For example, fluorine-rich spherules indicate that underwater vents created by volcanic activity injected a rich mixture of minerals into the subglacial environment. This was confirmed by DNA data, revealing a thriving community of thermophiles – microorganisms that live in very hot water only.

Then, it became plausible to hypothesise that volcanic eruptions occurred subglacially and formed a subglacial lake, whose waters ran into an interconnected system of channels, ultimately reaching the ice margin. Meltwater drained iron from pockets created where ice met bedrock, which then reached the ocean – thus inducing algal blooms.

We dated this drainage activity to a period when dust flux does not match ocean productivity. Thus, our study indicates that volcanoes in Antarctica had a role in delivering iron to the Southern Ocean, and potentially contributed to lowering CO2 levels in the atmosphere.

The ConversationOur research helps explain how volcanoes act on climate change. But it also uncovers more about iron fertilisation as a possible way to mitigate global warming.

Silvia Frisia, Associate Professor, School of Environmental and Life Sciences , University of Newcastle

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

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.

Antarctic ice shows Australia’s drought and flood risk is worse than thought


Anthony Kiem, University of Newcastle; Carly Tozer, University of Newcastle, and Tessa Vance, University of Tasmania

Australia is systematically underestimating its drought and flood risk because weather records do not capture the full extent of rainfall variability, according to our new research.

Our study, published today in the journal Hydrology and Earth System Sciences, uses Antarctic ice core data to reconstruct rainfall for the past 1,000 years for catchments in eastern Australia.

The results show that instrumental rainfall records – available for the past 100 years at best, depending on location – do not represent the full range of abnormally wet and dry periods that have occurred over the centuries.

In other words, significantly longer and more frequent wet and dry periods were experienced in the pre-instrumental period (that is, before the 20th century) compared with the period over which records have been kept.

Reconstructing prehistoric rainfall

There is no direct indicator of rainfall patterns for Australia before weather observations began. But, strange as it may sound, there is a link between eastern Australian rainfall and the summer deposition of sea salt in Antarctic ice. This allowed us to deduce rainfall levels by studying ice cores drilled from Law Dome, a small coastal ice cap in East Antarctica.

It might sound strange, but there’s a direct link between Antarctic ice and Australia’s rainfall patterns.
Tas van Ommen, Author provided

How can sea salt deposits in an Antarctic ice core possibly be related to rainfall thousands of kilometres away in Australia? It is because the processes associated with rainfall variability in eastern Australia – such as the El Niño/Southern Oscillation (ENSO), as well as other ocean cycles like the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) – are also responsible for variations in the wind and circulation patterns that cause sea salt to be deposited in East Antarctica (as outlined in our previous research).

By studying an ice record spanning 1,013 years, our results reveal a clear story of wetter wet periods and drier dry periods than is evident in Australia’s much shorter instrumental weather record.

For example, in the Williams River catchment, which provides water for the Newcastle region of New South Wales, our results showed that the longest dry periods lasted up to 12 years. In contrast, the longest dry spell since 1900 lasted just eight years.

Among wet periods, the difference was even more pronounced. The longest unusually wet spell in our ice record lasted 39 years – almost five times longer than the post-1900 maximum of eight years.

Busting myths about drought and flood risk

Although this does not tell us when the next major wet or dry period will happen, it does help us predict how often we can expect such events to occur, and how long they might last. This is critical information for water resource managers and planners, especially when our millennium-long record tells a very different story to the post-1900 instrumental record on which all water infrastructure, planning and policy is based.

Our results challenge the underlying assumptions that govern water resource management and infrastructure planning. These assumptions include:

  • that droughts longer than five years are rare;

  • that droughts or flood-dominated periods cannot last longer than about 15 years;

  • that drought and flood risk does not change over time, so a century of instrumental records is enough to gain a full understanding of the situation.

The fact that these assumptions are probably wrong is a concern. These principles are used to make crucial decisions, not just about predicting the likelihood and severity of droughts and floods themselves, but also about the design of infrastructure such as roads, reservoirs and buildings. Our study suggests that these decisions are being taken on the basis of incomplete information.

Cold case: drilling for ice to reveal long-term weather patterns.
Tessa Vance, Author provided

What’s more, Australia’s increasing population and development will mean that water demands and exposure to droughts and floods are likely to have been different in the past to what they are now (and will be in the future).

Therefore, given that the factors used to quantify risk are most likely wrong, it implies that current hydroclimatic risk assessments are not representative of the true level of risk.

This raises serious questions about water security and the robustness of existing water resource management, infrastructure design and catchment planning across eastern Australia and in other places where hydroclimatic risk is assessed on records that do not capture the full range of possible variation.

Water is a precious resource, meaning that we need the best knowledge about what our rainfall patterns are capable of delivering. Our findings can be used to better characterise and manage existing and future flood and drought risk. Forewarned is forearmed.

The Conversation

Anthony Kiem, Senior Lecturer – Hydroclimatology, University of Newcastle; Carly Tozer, Hydrologist, Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, University of Newcastle, 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.

Tipping point: how we predict when Antarctica’s melting ice sheets will flood the seas


Felicity Graham, University of Tasmania; David Gwyther, University of Tasmania; Lenneke Jong, University of Tasmania, and Sue Cook, University of Tasmania

Antarctica is already feeling the heat of climate change, with rapid melting and retreat of glaciers over recent decades.

Ice mass loss from Antarctica and Greenland contributes about 20% to the current rate of global sea level rise. This ice loss is projected to increase over the coming century.

A recent article on The Conversation raised the concept of “climate tipping points”: thresholds in the climate system that, once breached, lead to substantial and irreversible change.

Such a climate tipping point may occur as a result of the increasingly rapid decline of the Antarctic ice sheets, leading to a rapid rise in sea levels. But what is this threshold? And when will we reach it?

What does the tipping point look like?

The Antarctic ice sheet is a large mass of ice, up to 4 km thick in some places, and is grounded on bedrock. Ice generally flows from the interior of the continent towards the margins, speeding up as it goes.

Where the ice sheet meets the ocean, large sections of connected ice – ice shelves – begin to float. These eventually melt from the base or calve off as icebergs. The whole sheet is replenished by accumulating snowfall.

Emperor penguins at sunrise.
David Gwyther

Floating ice shelves act like a cork in a wine bottle, slowing down the ice sheet as it flows towards the oceans. If ice shelves are removed from the system, the ice sheet will rapidly accelerate towards the ocean, bringing about further ice mass loss.

A tipping point occurs if too much of the ice shelf is lost. In some glaciers, this may spark irreversible retreat.

Where is the tipping point?

One way to identify a tipping point involves figuring out how much shelf ice Antarctica can lose, and from where, without changing the overall ice flow substantially.

A recent study found that 13.4% of Antarctic shelf ice – distributed regionally across the continent – does not play an active role in ice flow. But if this “safety band” were removed, it would result in significant acceleration of the ice sheet.

The Totten Glacier calving front.
Esmee van Wijk/CSIRO

Antarctic ice shelves have been thinning at an overall rate of about 300 cubic km per year between 2003 and 2012 and are projected to thin even further over the 21st century. This thinning will move Antarctic ice shelves towards a tipping point, where irreversible collapse of the ice shelf and increase in sea levels may follow.

How do we predict when will it happen?

Some areas of West Antarctica may be already close to the tipping point. For example, ice shelves along the coast of the Amundsen and Bellingshausen Seas are the most rapidly thinning and have the smallest “safety bands” of all Antarctic ice shelves.

To predict when the “safety band” of ice might be lost, we need to project changes into the future. This requires better understanding of processes that remove ice from the ice sheet, such as melting at the base of ice shelves and iceberg calving.

Melting beneath ice shelves is the main source of Antarctic ice loss. It is driven by contact between warmer sea waters and the underside of ice shelves.

To figure out how much ice will be lost in the future requires knowledge of how quickly the oceans are warming, where these warmer waters will flow, and the role of the atmosphere in modulating these interactions. That’s a complex task that requires computer modelling.

Predicting how quickly ice shelves break up and form icebergs is less well understood and is currently one of the biggest uncertainties in future Antarctic mass loss. Much of the ice lost when icebergs calve occurs in the sporadic release of extremely large icebergs, which can be tens or even hundreds of kilometres across.

It is difficult to predict precisely when and how often large icebergs will break off. Models that can reproduce this behaviour are still being developed.

Scientists are actively researching these areas by developing models of ice sheets and oceans, as well as studying the processes that drive mass loss from Antarctica. These investigations need to combine long-term observations with models: model simulations can then be evaluated and improved, making the science stronger.

The link between ice sheets, oceans, sea ice and atmosphere is one of the least understood, but most important factors in Antarctica’s tipping point. Understanding it better will help us project how much sea levels will rise, and ultimately how we can adapt.

The Conversation

Felicity Graham, Ice Sheet Modeller, Antarctic Gateway Partnership, University of Tasmania; David Gwyther, Antarctic Coastal Ocean Modeller, University of Tasmania; Lenneke Jong, Cryosphere System Modeller, Antarctic Gateway Partnership & Antarctic Climate and Ecosystems CRC, University of Tasmania, and Sue Cook, Ice Shelf Glaciologist, Antarctic Climate and Ecosystems CRC, University of Tasmania

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

Frozen cones on Pluto – the first discovery of ice volcanoes?


Helen Maynard-Casely, Australian Nuclear Science and Technology Organisation

Ice volcanoes have shaped my life, and until today I didn’t even know if they actually existed. Now, thanks to NASA’s New Horizons spacecraft, there’s a good chance we’ve found a frozen volcanic cone on the surface of Pluto.

The first type of scientist I ever wanted to be was a volcanologist. Aged 12 the prospect of running up and down volcanoes and finding out what make them tick really enthused me.

Then, a pivotal moment for me, I must have been about 16, I watched ‘The Planets’ on TV and heard scientists talk of the possibility of ice volcanoes on the moons of Jupiter and Saturn (or cryo-volcanoes given that they would erupt a temperatures below −150 °C). For me, the fact that the solar system could possibly build volcanoes out of materials other than rock was captivating.

I steered away from an undergrad in geophysics to planetary science and my future of investigating icy stuff was set.

We’ve been searching for ice volcanoes in the solar system for a while and so far no ‘smoking caldera’ has turned up. For instance, we know that the surfaces of the icy moons Europa (orbiting Jupiter) and Titan (orbiting Saturn) are geologically young. However, the puzzle as to how they resurface is continuing as no ‘cryo-volcanic’ features have yet been spotted on these moons.

But now, 16 years after I watched that program, we’ve actually now got the first hint of a volcano of ice sitting on another body. In the pictures that New Horizon’s took of the Southern edge of Sputnik Platina, two volcano features have been spotted. They’ve been informally named Wright and Piccard Mons (I’ve been reliably informed that ‘Piccard’ is in reference to August Piccard the physicist and explorer).

Topographic maps of Piccard Mons (left) and Wright Mons (right).
NASA/JHUAPL/SWRI

It is early days in the discovery, but as Dr Oliver White, one of team of scientists looking through New Horizon’s data, said ‘These are big mountains with a large hole in their summit, and on Earth that generally means one thing – a volcano”.

The surface of Pluto hovers about 44 K (about -230°C) so, I’m sure you’re wondering how anything can be fluid enough at those chilly temperatures to erupt. This is because the ice that makes up these mountains is not pure, it will contain a significant amount of substances like methane, nitrogen and ammonia.

Freezing curve of ammonia-water system.

When mixed with water these materials, especially ammonia, cause an effect known as ‘freezing point depression’ lowering the temperature that the water becomes solid. In fact, anything that dissolves in water will have this effect, but ammonia is particularly effective at it – lowering the freezing temperature to -100 °C. Ok, so that’s not quite the -230°C of the surface so then this raises the possibility that internal heating may have play a role on Pluto too.

New Horizons is only a fifth of the way through downloading all of the data it collected as it shot past Pluto, there’s hopefully a lot more of these features yet to be identified. More importantly for knowing more about Wright and Piccard Mons is the spectroscopy data that’s on it way. Analysing the sunlight reflected off them will hopefully give us a hint of their chemistry. Once we have that, then we can start to build models of how these things have built and speculate if they are still active or not.

As well as sending all the data it has already collected, New Horizons is now on its way to the next encounter. Little nudges last week to the frighteningly fast trajectory is propelling the spacecraft towards 2014 MU69, a Kuiper Belt object that it will hopefully fly past in 2019. Given all that New Horizon’s has discovered (from only a fifth of the data) it is rather exciting to think what we are going to see further out.

The Conversation

Helen Maynard-Casely, Instrument Scientist, Australian Nuclear Science and Technology Organisation

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

Melting Antarctic ice sheets and sea level rise: a warning from the future


Andrew Glikson, Australian National University

The remote location of the Antarctic and Greenland polar ice sheets may leave us with the impression that developments in these regions have little effect on the climate and life in the temperate zones of the Earth, where most of us live. We may therefore be forgiven for asking why should we care when these changes are projected to unfold over tens to hundreds of years.

However, the stability of the polar regions is critical for maintaining a planet with the conditions that allowed the emergence of humans, agriculture and civilisation, as well as many other species. The polar ice sheets serve as “thermostats” of global temperatures from which cold air and cold ocean currents emanate, moderating the effects of solar radiation. The ice sheets regulate sea levels, store volumes of ice whose melting would raise sea level by up to 61 metres.

Unfortunately, what’s happening with the polar ice sheets now ought to warn humanity of what is to come.

For example, a recent paper suggested that melting Antarctic ice sheets could lead to 0.6-3.0 m of sea level rise by the year 2300. This is based on modelling of greenhouse gas emissions out to 2300.

If greenhouse gas emissions continue unchecked, the world may warm by 8–10℃ by 2300. Such a temperature rise could raise sea levels by tens of meters over hundreds of years.

The recent paper only looked at sea level rise from melting Antarctic ice sheets and does not take into account sea level rise contributions from the Greenland ice sheet (currently about 280 billion tonnes per year), which would more than double the Antarctic contribution.

Antarctic warming: Red represents areas where temperatures have increased the most during the last 50 years, particularly in West Antarctica.
NASA

Peering into the past to see the future

Much of the discussion in the paper and related papers appears to assume linear global warming – that is, little change to the rate of warming over time.

Little mention is made of feedbacks which could increase the rate of warming. Such feedbacks could arise from reducing albedo, where solar radiation usually strongly reflected by ice is replaced by strong absorption by water.

Other feedback processes associated with warming include methane release from permafrost and bogs; loss of vegetation; and fires.

In a recent article, former NASA climate scientist James Hansen and a large group of climate scientists point to observations arising from detailed studies of the recent history of the atmosphere-ocean-ice sheet system.

The climate records of the past — specifically, the Holocene (from about 10,000 years ago) and the Eemian interglacial period (about 115,000 to 130,000 years ago) — are closely relevant to future climate projections. These records include evidence for rapid disintegration of ice sheets in contact with the oceans as a result of feedback processes resulting in sea level rise to 5-9 m above current levels. All this during a period when mean global temperatures were near to only 1℃ above pre-industrial temperatures.

Sea levels reflect the overall global temperature and thus of global climate conditions. As shown by the position of the circles in the chart below, the ratio of sea level rise (SL) to temperature rise (TR) during the glacial-interglacial cycles was approximately between 10-15 metres per 1℃.

Plots of Temperature rise (relative to the pre-industrial age) vs relative sea level rise in (meters).

By contrast from around 1800 to the present sea level rose by an approximate ratio of 0.2-0.3 m per 1℃. This suggests significant further rise towards an equilibrium state between sea level and temperature. Thus, the points in the right-hand circle represent long-term temprature-sea level equilibria in the past while points in the left-hand circle represent where we’re at now, namely at an incipient stage moving toward future temprature-sea level equilibrium.

Why should long term climate change matter?

Due to the extreme rate of CO₂ and temperature rise during the 20th century relative to earlier events and the non-linearity of climate change trends the timing of sea level rise may be difficult to estimate.

Even on conservative estimates, current global warming is bound to have major consequences for human civilisation and for nature, as follows:

  • Further melting of the ice sheets will destroy the climate conditions which allowed agriculture and the rise of civilisation in the first place.

  • The lower parts of the world’s great rivers (Po, Rhine, Nile, Ganges, Indus, Mekong, Yellow, Mississippi, Amazon), where more than 3 billion people live and the bulk of agriculture and industry are located, sit no more than a few metres above sea level.

  • Further melting of the Antarctic and Greenland ice sheets can only result in sea level rises on the scale of tens of metres, changing the continent-ocean map of Earth.

Global temperatures have already risen 0.9℃ and continental temperatures 1.5℃ degrees above pre-industrial levels. If we account for the cooling effect of sulphur aerosols from industrial pollution, greenhouse gases have already contributed 2℃ of global warming. The current rate of global warming, faster than any observed in the geological record, is already having a major effect in many parts of the world in terms of droughts, fires, and storms.

According to James Hansen burning all the fossil fuels on Earth would result in warming of 20℃ over land areas and a staggering 30℃ at the poles, making “most of the planet uninhabitable by humans”.

In 2009 Joachim Hans Schellnhuber, Director of the Potsdam Climate Impacts Institute and Climate Advisor to the German Government, stated: “We’re simply talking about the very life support system of this planet”, constituting one of the most critical warnings science has ever issued to our species.

Mitigation plans proposed by governments would slow down the rate of carbon emissions but continuing emissions as well as feedbacks from ice melt, warming oceans, methane release and fires would continue to push temperatures upwards.

An effective technology required for global cooling efforts, if technically possible, would require investment on a scale not less than the trillions of dollars currently poured into armaments and war in the name of defence (more than $1.6 trillion in 2014).

Which planet do current decision makers think we are living on?

The Conversation

Andrew Glikson, Earth and paleo-climate scientist, Australian National University

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