If warming exceeds 2°C, Antarctica’s melting ice sheets could raise seas 20 metres in coming centuries



During the Pliocene, up to one third of Antarctica’s ice sheet melted, causing sea-level rise of 20 metres.
from http://www.shutterstock.com, CC BY-ND

Georgia Rose Grant, GNS Science and Timothy Naish, Victoria University of Wellington

We know that our planet has experienced warmer periods in the past, during the Pliocene geological epoch around three million years ago.

Our research, published today, shows that up to one third of Antarctica’s ice sheet melted during this period, causing sea levels to rise by as much as 20 metres above present levels in coming centuries.

We were able to measure past changes in sea level by drilling cores at a site in New Zealand, known as the Whanganui Basin, which contains shallow marine sediments of arguably the highest resolution in the world.

Using a new method we developed to predict the water level from the size of sand particle moved by waves, we constructed a record of global sea-level change with significantly more precision than previously possible.

The Pliocene was the last time atmospheric carbon dioxide concentrations were above 400 parts per million and Earth’s temperature was 2°C warmer than pre-industrial times. We show that warming of more than 2°C could set off widespread melting in Antarctica once again and our planet could be hurtling back to the future, towards a climate that existed three million years ago.




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Overshooting the Paris climate target

Last week we saw unprecedented global protests under the banner of Greta Thunberg’s #FridaysForFuture climate strikes, as the urgency of keeping global warming below the Paris Agreement target of 2°C hit home. Thunberg captured collective frustration when she chastised the United Nations for not acting earlier on the scientific evidence. Her plea resonated as she reminded us that:

With today’s emissions levels, that remaining CO₂ budget [1.5°C] will be entirely gone in less than eight and a half years.

At the current rate of global emissions we may be back in the Pliocene by 2030 and we will have exceeded the 2°C Paris target. One of the most critical questions facing humanity is how much and how fast global sea levels will rise.

According to the recent special report on the world’s oceans and cryosphere by the Intergovernmental Panel on Climate Change (IPCC), glaciers and polar ice sheets continue to lose mass at an accelerating rate, but the contribution of polar ice sheets, in particular the Antarctic ice sheet, to future sea level rise remains difficult to constrain.

If we continue to follow our current emissions trajectory, the median (66% probability) global sea level reached by the end of the century will be 1.2 metres higher than now, with two metres a plausible upper limit (5% probability). But of course climate change doesn’t magically stop after the year 2100.




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Drilling back to the future

To better predict what we are committing the world’s future coastlines to we need to understand polar ice sheet sensitivity. If we want to know how much the oceans will rise at 400ppm CO₂, the Pliocene epoch is a good comparison.

Back in 2015, we drilled cores of sediment deposited during the Pliocene, preserved beneath the rugged hill country at the Whanganui Basin. One of us (Timothy Naish) has worked in this area for almost 30 years and identified more than 50 fluctuations in global sea level during the last 3.5 million years of Earth’s history. Global sea levels had gone up and down in response to natural climate cycles, known as Milankovitch cycles, which are caused by long-term changes in Earths solar orbit every 20,000, 40,000 and 100,000 years. These changes in turn cause polar ice sheets to grow or melt.

While sea levels were thought to have fluctuated by several tens of metres, up until now efforts to reconstruct the precise amplitude had been thwarted by difficulties due to Earth deformation processes and the incomplete nature of many of the cycles.

Our research used a well-established theoretical relationship between the size of the particles transported by waves on the continental shelf and the depth to the seabed. We then applied this method to 800 metres of drill core and outcrop, representing continuous sediment sequences that span a time period from 2.5 to 3.3 million years ago.

We show that during the Pliocene, global sea levels regularly fluctuated between five to 25 metres. We accounted for local tectonic land movements and regional sea-level changes caused by gravitational and crustal changes to determine the sea-level estimates, known as the PlioSeaNZ sea-level record. This provides an approximation of changes in global mean sea level.

Antarctica’s contribution to sea-level rise

Our study also shows that most of the sea-level rise during the Pliocene came from Antarctica’s ice sheets. During the warm Pliocene, the geography of Earth’s continents and oceans and the size of polar ice sheets were similar to today, with only a small ice sheet on Greenland during the warmest period. The melting of the Greenland ice sheet would have contributed at most five metres to the maximum 25 metres of global sea-level rise recorded at Whanganui Basin.

Of critical concern is that over 90% of the heat from global warming to date has gone into the ocean. Much of it has gone into the Southern Ocean, which bathes the margins of Antarctica’s ice sheet.




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Already, we are observing warm circumpolar deep water upwelling and entering ice shelf cavities in several sites around Antarctica today. Along the Amundsen Sea coast of West Antarctica, where the ocean has been heating the most, the ice sheet is thinning and retreating the fastest. One third of Antarctica’s ice sheet — the equivalent to up to 20 metres of sea-level rise — is grounded below sea level and vulnerable to widespread collapse from ocean heating.

Our study has important implications for the stability and sensitivity of the Antarctic ice sheet and its potential to contribute to future sea levels. It supports the concept that a tipping point in the Antarctic ice sheet may be crossed if global temperatures are allowed to rise by more than 2℃. This could result in large parts of the ice sheet being committed to melt-down over the coming centuries, reshaping shorelines around the world.The Conversation

Georgia Rose Grant, Postdoctoral Research Assistant, Paleontology Team, GNS Science and Timothy Naish, Professor, Victoria University of Wellington

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Explainer: what happens when magnetic north and true north align?



Very rarely, depending on where you are in the world, your compass can actually point to true north.
https://www.shutterstock.com

Paul Wilkes, CSIRO

At some point in recent weeks, a once-in-a-lifetime event happened for people at Greenwich in the United Kingdom.

Magnetic compasses at the historic London area, known as the home of the Prime Meridian, were said to have pointed directly at the north geographic pole for the first time in 360 years.

This means that, for someone at Greenwich, magnetic north (the direction in which a compass needle points) would have been in exact alignment with geographic north.

Geographic north (also called “true north”) is the direction towards the fixed point we call the North Pole.

Magnetic north is the direction towards the north magnetic pole, which is a wandering point where the Earth’s magnetic field goes vertically down into the planet.

The north magnetic pole is currently about 400km south of the north geographic pole, but can move to about 1,000km away.

The lines of the Earth’s magnetic field come vertically out of the Earth at the south magnetic pole and go vertically down into the Earth at the north magnetic pole.
Nasky/Shutterstock

How do the norths align?

Magnetic north and geographic north align when the so-called “angle of declination”, the difference between the two norths at a particular location, is 0°.

Declination is the angle in the horizontal plane between magnetic north and geographic north. It changes with time and geographic location.

The declination angle varies between -90° and +90°.
Author provided

On a map of the Earth, lines along which there is zero declination are called agonic lines. Agonic lines follow variable paths depending on time variation in the Earth’s magnetic field.

Currently, zero declination is occurring in some parts of Western Australia, and will likely move westward in coming years.

That said, it’s hard to predict exactly when an area will have zero declination. This is because the rate of change is slow and current models of the Earth’s magnetic field only cover a few years, and are updated at roughly five-year intervals.

At some locations, alignment between magnetic north and geographic north is very unlikely at any time, based on predictions.

The ever-changing magnetic poles

Most compasses point towards Earth’s north magnetic pole, which is usually in a different place to the north geographic pole. The location of the magnetic poles is constantly changing.

Earth’s magnetic poles exist because of its magnetic field, which is produced by electric currents in the liquid part of its core. This magnetic field is defined by intensity and two angles, inclination and declination.

The relationship between geographic location and declination is something people using magnetic compasses have to consider. Declination is the reason a compass reading for north in one location is different to a reading for north in another, especially if there is considerable distance between both locations.




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Bush walkers have to be mindful of declination. In Perth, declination is currently close to 0° but in eastern Australia it can be up to 12°. This difference can be significant. If a bush walker following a magnetic compass disregards the local value of declination, they may walk in the wrong direction.

The polarity of Earth’s magnetic poles has also changed over time and has undergone pole reversals. This was significant as we learnt more about plate tectonics in the 1960s, because it linked the idea of seafloor spreading from mid-ocean ridges to magnetic pole reversals.

Geographic north

Geographic north, perhaps the more straightforward of the two, is the direction that points straight at the North Pole from any location on Earth.

When flying an aircraft from A to B, we use directions based on geographic north. This is because we have accurate geographic locations for places and need to follow precise routes between them, usually trying to minimise fuel use by taking the shortest route. All GPS navigation uses geographic location.




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Geographic coordinates, latitude and longitude, are defined relative to Earth’s spheroidal shape. The geographic poles are at latitudes of 90°N (North Pole) and 90°S (South Pole), whereas the Equator is at 0°.

An alignment at Greenwich

For hundreds of years, declination at Greenwich was negative, meaning compass needles were pointing west of true north.

At the time of writing this article I used an online calculator to discover that, at the Greenwich Observatory, the Earth’s magnetic field currently has a declination just above zero, about +0.011°.

The average rate of change in the area is about 0.19° per year, which at Greenwich’s latitude represents about 20km per year. This means next year, locations about 20km west of Greenwich will have zero declination.

It’s impossible to say how long compasses at Greenwich will now point east of true north.

Regardless, an alignment after 360 years at the home of the Prime Meridian is undoubtedly a once-in-a-lifetime occurrence.The Conversation

Paul Wilkes, Senior Research Geophysicist, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The air above Antarctica is suddenly getting warmer – here’s what it means for Australia



Antarctic winds have a huge effect on weather in other places.
NASA Goddard Space Flight Center/Flickr, CC BY-SA

Harry Hendon, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Eun-Pa Lim, Australian Bureau of Meteorology, and Griffith Young, Australian Bureau of Meteorology

Record warm temperatures above Antarctica over the coming weeks are likely to bring above-average spring temperatures and below-average rainfall across large parts of New South Wales and southern Queensland.

The warming began in the last week of August, when temperatures in the stratosphere high above the South Pole began rapidly heating in a phenomenon called “sudden stratospheric warming”.




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In the coming weeks the warming is forecast to intensify, and its effects will extend downward to Earth’s surface, affecting much of eastern Australia over the coming months.

The Bureau of Meteorology is predicting the strongest Antarctic warming on record, likely to exceed the previous record of September 2002.

(Left) Observation of September 2002 stratospheric warming compared to (right) 2019 forecast for September.
The forecast for 2019 was provided by the Australian Bureau of Meteorology and was initialised on August 30, 2019.

What’s going on?

Every winter, westerly winds – often up to 200km per hour – develop in the stratosphere high above the South Pole and circle the polar region. The winds develop as a result of the difference in temperature over the pole (where there is no sunlight) and the Southern Ocean (where the sun still shines).

As the sun shifts southward during spring, the polar region starts to warm. This warming causes the stratospheric vortex and associated westerly winds to gradually weaken over the period of a few months.

However, in some years this breakdown can happen faster than usual. Waves of air from the lower atmosphere (from large weather systems or flow over mountains) warm the stratosphere above the South Pole, and weaken or “mix” the high-speed westerly winds.

Very rarely, if the waves are strong enough they can rapidly break down the polar vortex, actually reversing the direction of the winds so they become easterly. This is the technical definition of “sudden stratospheric warming.”

Although we have seen plenty of weak or moderate variations in the polar vortex over the past 60 years, the only other true sudden stratospheric warming event in the Southern Hemisphere was in September 2002.

In contrast, their northern counterpart occurs every other year or so during late winter of the Northern Hemisphere because of stronger and more variable tropospheric wave activity.

What can Australia expect?

Impacts from this stratospheric warming are likely to reach Earth’s surface in the next month and possibly extend through to January.

Apart from warming the Antarctic region, the most notable effect will be a shift of the Southern Ocean westerly winds towards the Equator.

For regions directly in the path of the strongest westerlies, which includes western Tasmania, New Zealand’s South Island, and Patagonia in South America, this generally results in more storminess and rainfall, and colder temperatures.

But for subtropical Australia, which largely sits north of the main belt of westerlies, the shift results in reduced rainfall, clearer skies, and warmer temperatures.

Past stratospheric warming events and associated wind changes have had their strongest effects in NSW and southern Queensland, where springtime temperatures increased, rainfall decreased and heatwaves and fire risk rose.

The influence of the stratospheric warming has been captured by the Bureau’s climate outlooks, along with the influence of other major climate drivers such as the current positive Indian Ocean Dipole, leading to a hot and dry outlook for spring.

Anomalous Australian climate conditions during the nine most significant polar vortex weakening years (1979, 1988, 2000, 2002, 2004, 2005, 2012, 2013, 2016) on both maximum and minimum temperatures, and rainfall for October-November, as compared to all other years between 1979-2016.
Bureau of Meteorology

Effects on the ozone hole and Antarctic sea ice

One positive note of sudden stratospheric warming is the reduction – or even absence altogether – of the spring Antarctic ozone hole. This is for two reasons.

First, the rapid rise of temperatures in the upper atmosphere means the super cold polar stratospheric ice clouds, which are vital for the chemical process that destroys ozone, may not even form.

Secondly, the disrupted winds carry more ozone-rich air from the tropics to the polar region, helping repair the ozone hole.

We also expect an enhanced decline in Antarctic sea ice between October and January, particularly in the eastern Ross Sea and western Amundsen Sea, as more warm water moves towards the poles due to the weaker westerly winds.




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Thanks to improvements in modelling and the Bureau’s new supercomputer, these types of events can be forecast better than ever before. Compared to 2002, when we didn’t know much about the event until after it had happened, this time we’ve had almost three weeks’ notice that a very strong warming event was coming. We also know much more about the process that has been set in train, that will affect our weather over the next one to four months.The Conversation

Harry Hendon, Senior Principal Research Scientist, Australian Bureau of Meteorology; Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology; Eun-Pa Lim, Senior research scientist, Australian Bureau of Meteorology, and Griffith Young, Senior IT Officer, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia wants to install military technology in Antarctica – here’s why that’s allowed



Technology, such as satellite systems, can be used for both military and scientific purposes.
Shutterstock

Tony Press, University of Tasmania

This week, the ABC revealed that the Australian Defence Force wants to roll out military technology in Antarctica.

The article raises the issue of what is, or is not, legitimate use of technology under the Antarctic Treaty. And it has a lot to do with how technology is used and provisions in the treaty.

The Antarctic Treaty was negotiated in the late 1950s, during the Cold War. Its purpose was to keep Antarctica separate from any Cold War conflict, and any arguments over sovereignty claims.




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The words used in the treaty reflect the global politics and technologies back then, before there were satellites and GPS systems. But its provisions and prohibitions are still relevant today.

The opening provision of the Antarctic Treaty, which came into force in 1961, says:

Antarctica shall be used for peaceful purposes only. There shall be prohibited, [among other things], any measures of a military nature, such as the establishment of military bases and fortifications, the carrying out of military manoeuvres, as well as the testing of any type of weapons.

The treaty also prohibits “any nuclear explosions in Antarctica” and disposal of radioactive waste. What the treaty does not do, however, is prohibit countries from using military support in their peaceful Antarctic activities.

Many Antarctic treaty parties, including Australia, New Zealand, the United Kingdom, the US, Chile and Argentina, rely on military support for their research. This includes the use of ships, aircraft, personnel and specialised services like aircraft ground support.

In fact, the opening provision of the treaty is clarified by the words:

the present Treaty shall not prevent the use of military personnel or equipment for scientific research or for any other peaceful purpose.

It would be a breach of the treaty if “military exercises” were being conducted in Antarctica, or if military equipment was being used for belligerent purposes. But the treaty does not deal specifically with technology. It deals with acts or actions. The closest it gets to technology is the term “equipment” as used above.

Dual use technology

So-called “dual use” technology – which that can be used for both peaceful and military purposes – is allowed in Antarctica in support of science.




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The term is often used to describe technology such as the widely-used GPS, which relies on satellites and a worldwide system of ground-based receiving stations. Norway’s “Trollsat”, China’s “Beidou”, and Russia’s “GLONASS” systems are similar, relying on satellites and ground stations for their accuracy.

What’s more, modern science heavily relies on satellite technology and the use of Antarctic ground stations for data gathering and transmission.

And scientific equipment, like ice-penetrating radars, carried on aircraft, drones, and autonomous airborne vehicles are being used extensively to understand the Antarctic continent itself and how it’s changing.

Much, if not all, of this technology could have “dual use”. But its use is not contrary to the Antarctic Treaty.

In fact, the use of this equipment for “scientific research” or a “peaceful purpose” is not only legitimate, it’s also essential for Antarctic research, and global understanding of the health of our planet.




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The technologies Australia deploys in Antarctica all relate to its legitimate Antarctic operations and to science.

There are also facilities in Antarctica used to monitor potential military-related activities elsewhere in the world, such as the monitoring stations used under the Comprehensive Nuclear Test Ban Treaty.

The circumstances under which modern technology would, or could be, used against the provisions of the Antarctic Treaty have not been tested. But the activity would have to go beyond “dual purpose” and not be for science or peaceful purposes.

Science in Antarctica is open to scrutiny

Science in Antarctica is very diverse, from space sciences to ecosystem science, and 29 countries have active research programs there.

And since Antarctica plays a significant role in the global climate system, much modern Antarctic research focuses on climate science and climate change.

But there has been speculation about whether Antarctica is crucial to the development of alternatives to GPS (for example, by Russia and China) that could also be used in warfare as well as for peaceful purposes. It’s unclear whether using ground stations in Antarctica is essential for such a purpose.

For instance, Claire Young, a security analyst writing for the Australian Strategic Policy Institute, said the accuracy of China’s Beidou satellite has already been improved by international testing, so testing in Antarctica will make very little difference.




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This leads to another important provision of the Antarctic Treaty.

The treaty foreshadowed compliance problems in the remote and hostile continent by including an open ended provision for any Antarctic Treaty Party to inspect any Antarctic facility.

In other words, any party has complete freedom to access all parts of Antarctica at any time to inspect ships, aircraft, equipment, or any other facility, and even use “aerial observations” for inspection. This means the activities of all parties, and all actions in Antarctica, are available for open scrutiny.

This inspection regime is important because inspections can be used to determine if modern technology on the continent is, in fact, being used for scientific or peaceful purposes, in line with the provisions of the treaty.The Conversation

Tony Press, Adjunct Professor, Institute for Marine and Antarctic Studies, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New research shows that Antarctica’s largest floating ice shelf is highly sensitive to warming of the ocean



Since the last ice age, the ice sheet retreated over a thousand kilometres in the Ross Sea region, more than any other region on the continent.
Rich Jones, CC BY-ND

Dan Lowry, Victoria University of Wellington

Scientists have long been concerned about the potential collapse of the West Antarctic Ice Sheet and its contribution to global sea level rise. Much of West Antarctica’s ice lies below sea level, and warming ocean temperatures may lead to runaway ice sheet retreat.

This process, called marine ice sheet instability, has already been observed along parts of the Amundsen Sea region, where warming of the ocean has led to melting underneath the floating ice shelves that fringe the continent. As these ice shelves thin, the ice grounded on land flows more rapidly into the ocean and raises the sea level.

Although the Amundsen Sea region has shown the most rapid changes to date, more ice actually drains from West Antarctica via the Ross Ice Shelf than any other area. How this ice sheet responds to climate change in the Ross Sea region is therefore a key factor in Antarctica’s contribution to global sea level rise in the future.

Periods of past ice sheet retreat can give us insights into how sensitive the Ross Sea region is to changes in ocean and air temperatures. Our research, published today, argues that ocean warming was a key driver of glacial retreat since the last ice age in the Ross Sea. This suggests that the Ross Ice Shelf is highly sensitive to changes in the ocean.




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History of the Ross Sea

Since the last ice age, the ice sheet retreated more than 1,000km in the Ross Sea region – more than any other region on the continent. But there is little consensus among the scientific community about how much climate and the ocean have contributed to this retreat.

Much of what we know about the past ice sheet retreat in the Ross Sea comes from rock samples found in the Transantarctic Mountains. Dating techniques allow scientists to determine when these rocks were exposed to the surface as the ice around them retreated. These rock samples, which were collected far from where the initial ice retreat took place, have generally led to interpretations in which the ice sheet retreat happened much later than, and independently of, the rise in air and ocean temperatures following the last ice age.

But radiocarbon ages from sediments in the Ross Sea suggest an earlier retreat, more in line with when climate began to warm from the last ice age.

An iceberg floating in the Ross Sea – an area that is sensitive to warming in the ocean.
Rich Jones, CC BY-ND

Using models to understand the past

To investigate how sensitive this region was to past changes, we developed a regional model of the Antarctic ice sheet. The model works by simulating the physics of the ice sheet and its response to changes in ocean and air temperatures. The simulations are then compared to geological records to check accuracy.

Our main findings are that warming of the ocean and atmosphere were the main causes of the major glacial retreat that took place in the Ross Sea region since the last ice age. But the dominance of these two controls in influencing the ice sheet evolved through time. Although air temperatures influenced the timing of the initial ice sheet retreat, ocean warming became the main driver due to melting of the Ross Ice Shelf from below, similar to what is currently observed in the Amundsen Sea.

The model also identifies key areas of uncertainty of past ice sheet behaviour. Obtaining sediment and rock samples and oceanographic data would help to improve modelling capabilities. The Siple Coast region of the Ross Ice Shelf is especially sensitive to changes in melt rates at the base of the ice shelf, and is therefore a critical region to sample.




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Implications for the future

Understanding processes that were important in the past allows us to improve and validate our model, which in turn gives us confidence in our future projections. Through its history, the ice sheet in the Ross Sea has been sensitive to changes in ocean and air temperatures. Currently, ocean warming underneath the Ross Ice Shelf is the main concern, given its potential to cause melting from below.

Challenges remain in determining exactly how ocean temperatures will change underneath the Ross Ice Shelf in the coming decades. This will depend on changes to patterns of ocean circulation, with complex interactions and feedback between sea ice, surface winds and melt water from the ice sheet.

Given the sensitivity of ice shelves to ocean warming, we need an integrated modelling approach that can accurately reproduce both the ocean circulation and dynamics of the ice sheet. But the computational cost is high.

Ultimately, these integrated projections of the Southern Ocean and Antarctic ice sheet will help policymakers and communities to develop meaningful adaptation strategies for cities and coastal infrastructure exposed to the risk of rising seas.The Conversation

Dan Lowry, PhD candidate, Victoria University of Wellington

This article is republished from The Conversation under a Creative Commons license. Read the original article.