How Antarctic ice melt can be a tipping point for the whole planet’s climate

Melting Antarctic ice can trigger effects on the other side of the globe. NASA/Jane Peterson

Chris Turney, UNSW; Jonathan Palmer, UNSW; Peter Kershaw, Monash University; Steven Phipps, University of Tasmania, and Zoë Thomas, UNSW

Melting of Antarctica’s ice can trigger rapid warming on the other side of the planet, according to our new research which details how just such an abrupt climate event happened 30,000 years ago, in which the North Atlantic region warmed dramatically.

This idea of “tipping points” in Earth’s system has had something of a bad rap ever since the 2004 blockbuster The Day After Tomorrow purportedly showed how melting polar ice can trigger all manner of global changes.

But while the movie certainly exaggerated the speed and severity of abrupt climate change, we do know that many natural systems are vulnerable to being pushed into different modes of operation. The melting of Greenland’s ice sheet, the retreat of Arctic summer sea ice, and the collapse of the global ocean circulation are all examples of potential vulnerability in a future, warmer world.

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Read more: Chasing ice: how ice cores shape our understanding of ancient climate.

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Of course it is notoriously hard to predict when and where elements of Earth’s system will abruptly tip into a different state. A key limitation is that historical climate records are often too short to test the skill of our computer models used to predict future environmental change, hampering our ability to plan for potential abrupt changes.

Fortunately, however, nature preserves a wealth of evidence in the landscape that allows us to understand how longer time-scale shifts can happen.

Core values

One of the most important sources of information on past climate tipping points are the kilometre-long cores of ice drilled from the Greenland and Antarctic ice sheets, which preserve exquisitely detailed information stretching back up to 800,000 years.

The Greenland ice cores record massive, millennial-scale swings in temperature that have occurred across the North Atlantic region over the past 90,000 years. The scale of these swings is staggering: in some cases temperatures rose by 16℃ in just a few decades or even years.

Twenty-five of these major so-called Dansgaard–Oeschger (D-O) warming events have been identified. These abrupt swings in temperature happened too quickly to have been caused by Earth’s slowly changing orbit around the Sun. Fascinatingly, when ice cores from Antarctica are compared with those from Greenland, we see a “seesaw” relationship: when it warms in the north, the south cools, and vice versa.

Attempts to explain the cause of this bipolar seesaw have traditionally focused on the North Atlantic region, and include melting ice sheets, changes in ocean circulation or wind patterns.

But as our new research shows, these might not be the only cause of D-O events.

Our new paper, published today in Nature Communications, suggests that another mechanism, with its origins in Antarctica, has also contributed to these rapid seesaws in global temperature.

Tree of knowledge

The 30,000-year-old key to climate secrets.
Chris Turney, Author provided

We know that there have been major collapses of the Antarctic ice sheet in the past, raising the possibility that these may have tipped one or more parts of the Earth system into a different state. To investigate this idea, we analysed an ancient New Zealand kauri tree that was extracted from a peat swamp near Dargaville, Northland, and which lived between 29,000 and 31,000 years ago.

Through accurate dating, we know that this tree lived through a short D-O event, during which (as explained above) temperatures in the Northern Hemisphere would have risen. Importantly, the unique pattern of atmospheric radioactive carbon (or carbon-14) found in the tree rings allowed us to identify similar changes preserved in climate records from ocean and ice cores (the latter using beryllium-10, an isotope formed by similar processes to carbon-14). This tree thus allows us to compare directly what the climate was doing during a D-O event beyond the polar regions, providing a global picture.

The extraordinary thing we discovered is that the warm D-O event coincided with a 400-year period of surface cooling in the south and a major retreat of Antarctic ice.

When we searched through other climate records for more information about what was happening at the time, we found no evidence of a change in ocean circulation. Instead we found a collapse in the rain-bearing Pacific trade winds over tropical northeast Australia that was coincident with the 400-year southern cooling.

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Read more: Two centuries of continuous volcanic eruption may have triggered the end of the ice age.

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To explore how melting Antarctic ice might cause such dramatic change in the global climate, we used a climate model to simulate the release of large volumes of freshwater into the Southern Ocean. The model simulations all showed the same response, in agreement with our climate reconstructions: regardless of the amount of freshwater released into the Southern Ocean, the surface waters of the tropical Pacific nevertheless warmed, causing changes to wind patterns that in turn triggered the North Atlantic to warm too.

Future work is now focusing on what caused the Antarctic ice sheets to retreat so dramatically. Regardless of how it happened, it looks like melting ice in the south can drive abrupt global change, something of which we should be aware in a future warmer world.

Chris Turney, Professor of Earth Sciences and Climate Change, UNSW; Jonathan Palmer, Research Fellow, School of Biological, Earth and Environmental Sciences., UNSW; Peter Kershaw, Emeritus Professor, Earth, Atmosphere and Environment, Monash University; Steven Phipps, Palaeo Ice Sheet Modeller, University of Tasmania, and Zoë Thomas, Research Associate, UNSW

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

David Attenborough says the Great Barrier Reef is in ‘grave danger’ – it’s time to step up

Ove Hoegh-Guldberg, The University of Queensland and Tyrone Ridgway, The University of Queensland

Over three weeks, Australians have been taken on an incredible journey through the biology, beauty and wonder of the Great Barrier Reef, guided by Sir David Attenborough.

As individuals who have had the privilege of working on the Reef for much of our lives, the wonderful storytelling, exquisite photography and stunning production of the Great Barrier Reef with David Attenborough has been inspiring. It’s a great reminder of how lucky we are to have this wonder of nature right on our doorstep.

Particularly special has been the wonderful black-and-white footage of Sir David’s first visit to the Reef in 1957, a trip down memory lane. His attachment and fascination with the Reef are hard to dismiss.

However, as the curtain closes on this wonderful series, Sir David concludes that the Reef that he visited nearly 60 years ago is very different from today.

Research backs up this personal experience. The Australian Institute of Marine Science has shown that the Great Barrier Reef has lost around 50% of its coral cover between 1985 and 2012.

A reef in peril

The Great Barrier Reef is in grave danger. The twin perils brought by climate change – an increase in the temperature of the ocean and in its acidity – threaten its very existence. – Sir David Attenborough

As this television series has aired in Australia, an underwater heatwave has caused coral bleaching on 93% of the reefs that make up the Great Barrier Reef. Up to 50% of corals in the worst-affected regions may die as a result of this bleaching.

We should not be too surprised. Reef scientists have been warning about this for decades. In 1998, the warmest year on record at the time, the world lost around 16% of its coral reefs in the first global-scale mass coral bleaching event.

Before the current bleaching, the reef bleached severely in 1998 and 2002, with a substantial bleaching event in 2006 around the Keppel Islands. Outside these events, there has been moderate mass bleaching on the reef since the early 1980s (particularly 1983 and 1987), although never to the extent and intensity that we are witnessing today.

Rising sea temperatures

The current bleaching event has drawn widespread media coverage. One of the arguments we have seen raised is that coral bleaching is natural – and that the reef will bounce back as it always has, or even adapt to warming seas.

It is true that certain coral species, and even certain individual colonies within the same species, do perform better than others when stressed by warmer-than-normal sea temperatures. However, the extent of these differences is only 1-2℃. Given that even moderate climate change projections involve temperatures 2-3℃ higher than today, these differences offer little comfort for reefs like the Great Barrier Reef in a warmer world.

The observation that corals grow in warm areas of the globe is a demonstration that corals can and do adapt to local temperatures. However, the time frames involved are hundreds of years, not a single decade. Current rates of warming are much faster than anything for tens of millions of years, which makes the prospect of evolution keeping pace with a changing ocean even more improbable.

Mass bleaching is a new phenomenon that was first reported in the early 1980s. Before this, there are no reports of corals bleaching en masse across any coral reef or ocean region.

Experts are in agreement that mass coral bleaching and death on the Great Barrier Reef is driven by climate change resulting from human activities (mainly burning fossil fuels). This is the conclusion at the heart of the latest consensus of the United Nations scientific report.

Rising sea temperatures coupled with strong El Niños are unfortunately pushing corals to their thermal tolerance limits and beyond. It only takes a temperature increase of 1-2℃ to disrupt the special relationship between corals and tiny marine algae that live inside their tissue, resulting in bleached corals.

In fact, as CO₂ concentrations rise, sea temperatures will continue to climb – increasing the likelihood that mass coral bleaching events will become more frequent and more destructive. Recent research has shown that near-future increases in local temperature of as little as 0.5℃ may lead to significant degradation of the Great Barrier Reef.

Rising temperatures are not the only climate threat. Cyclones are predicted to become stronger (if less frequent) in a warmer world. Since 2005 there have been eight cyclones on the reef of category 3 or above – more than previous decades. We would argue this is evidence that these predictions are already coming true and form part of our current reality.

Heat stress is not just affecting corals on the Great Barrier Reef either. We are seeing reports of bleaching across all of Australia’s coral real estate (Coral Sea, Torres Strait, Kimberley, North West Shelf), the South Pacific and the central and western Indian Ocean.

It is likely only a matter of time before we start to see reports of bleaching from other coral reefs around the world. We are indeed dealing with changing times and a global issue.

It’s not too late to act

It’s not too late to act – but we will need very deep and significant action to occur within three to five years or face a collapse of ecosystems like the Great Barrier Reef.

Climate change is just one of the threats facing the Great Barrier Reef. Fortunately, it is not too late to give the reef a fighting chance.

Ove Hoegh-Guldberg on the future of the reef

However, it does require strong, immediate and decisive action from our political leaders.

In the lead-up to the federal election, we believe that four major steps are required by our leaders to ensure a future for the Reef:

1. Mitigate: we need to – as per the Paris Agreement – keep average global surface temperature increases to below 2.0°C, and hopefully 1.5°C in the long term. This means we must adopt a pathway that will bring our greenhouse gas emissions to zero over the next few decades. Our leaders must live up to the global agreement that they committed to in Paris at COP21.
2. Invest: we need to ultimately close our coal mines and stop searching for more fossil fuels. The experts tell us that we must leave 80% of known fossil fuels in the ground. Let’s invest in coral, renewables and the planet, and not in coal, emissions and ecosystem collapse.
3. Strengthen: we need an urgent and concerted effort to reduce other non-climate change threats to build the resilience of the reef so it can better withstand the impacts of climate change over the coming years.
4. Integrate: Australian and Queensland governments have begun a process to address declining reef health through the Reef 2050 Long-term Sustainability Plan. This plan has a strong focus on coastal water quality. The 2050 Reef Plan and its resourcing will need to consider climate change – especially given that it is likely to make achieving the objectives of the plan even more challenging and impossible (if no action). Otherwise we run the risk of ending up with a great plan for improving water quality by 2050 but no Great Barrier Reef.

We hope that Sir David Attenborough will help inspire Australians to demand action from their political leaders to ensure that this natural wonder of the world continues to inspire, employ, educate and generate income for generations to come.

It seems fitting to end with Sir David’s closing words with a call to our political leaders and fellow Australians:

Do we really care so little about the earth upon which we live that we don’t wish to protect one of its greatest wonders from the consequences of our behaviours?

After all, it is our Great Barrier Reef – let’s keep it great.

Or at least let’s fight to keep it.

Ove Hoegh-Guldberg, Director, Global Change Institute, The University of Queensland and Tyrone Ridgway, Healthy Oceans Program Manager, Global Change Institute, The University of Queensland

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

 

Denialism

Denialism is a person’s choice to deny certain particular facts.  It is an essentially irrational belief where the person substitutes his or her personal opinion for established knowledge. Indeed, one of the hallmarks of denialism is a failure to recognise the distinction between opinions and facts.

Denialism should not be confused with modern scientific skepticism, which is the challenging of beliefs that are unscientific, irrational or based on insufficient evidence.  Instead of denying facts, modern skeptics test claims by analysing whether they are supported by adequate empirical evidence. Denialism is the a priori rejection of ideas without objective consideration.

The philosophical skepticism of the Academic Skeptics and Pyrrhonists in Classical Greece (which was quite different to modern skepticism) consisted of doubting whether there can be any knowledge or facts at all, rather than denying particular facts.

Science denialism is the rejection of basic facts and concepts that are undisputed, well-supported parts of the scientific consensus on a subject, in favour of radical and controversial opinions of an unscientific nature. For example, the term climate change denialist is applied to people who argue against the scientific consensus that the global warming of planet Earth is a real and occurring event primarily caused by human activity. 

The term evolution denialist or ‘creationist’ is applied to people who argue against the fact that life on Earth has evolved from earlier forms, instead of having been created by a supernatural being in its current form.

Other instances include Holocaust denialism, AIDS denialism, vaccination denialism, and Flat-Earthism. The various forms of denialism present the common feature of the person rejecting overwhelming evidence, often with attempts to deny the existence of a scientific consensus or alternatively to allege a conspiracy theory to fake or conceal the evidence. Denialism is commonly one of the foundations of quackery and other varieties of woo.

The motivations and causes of denialism include irrationality, religion and self-interest (political, economic or financial), beliefs in conspiracy theories or even defence mechanisms meant to protect the psyche of the denialist against mentally disturbing facts and ideas.