Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month


Dana M Bergstrom, University of Wollongong; Andrew Klekociuk, University of Tasmania; Diana King, University of Wollongong, and Sharon Robinson, University of Wollongong

While the world rightfully focuses on the COVID-19 pandemic, the planet is still warming. This summer’s Antarctic weather, as elsewhere in the world, was unprecedented in the observed record.

Our research, published today in Global Change Biology, describes the recent heatwave in Antarctica. Beginning in late spring east of the Antarctic Peninsula, it circumnavigated the continent over the next four months. Some of our team spent the summer in Antarctica observing these temperatures and the effect on natural systems, witnessing the heatwave first-hand.

Antarctica may be isolated from other continents by the Southern Ocean, but has worldwide impacts. It drives the global ocean conveyor belt, a constant system of deep-ocean circulation which transfers oceanic heat around the planet, and its melting ice sheet adds to global sea level rise.

Antarctica represents the simple, extreme end of conditions for life. It can be seen as a ‘canary in the mine’, demonstrating patterns of change we can expect to see elsewhere.

A heatwave in the coldest place on Earth

Most of Antarctica is ice-covered, but there are small ice-free oases, predominantly on the coast. Collectively 0.44% of the continent, these unique areas are important biodiversity hotspots for penguins and other seabirds, mosses, lichens, lakes, ponds and associated invertebrates.

This summer, Casey Research Station, in the Windmill Islands oasis, experienced its first recorded heat wave. For three days, minimum temperatures exceeded zero and daily maximums were all above 7.5°C. On January 24, its highest maximum of 9.2°C was recorded, almost 7°C above Casey’s 30-year mean for the month.




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The arrival of warm, moist air during this weather event brought rain to Davis Research Station in the normally frigid, ice-free desert of the Vestfold Hills. The warm conditions triggered extensive meltwater pools and surface streams on local glaciers. These, together with melting snowbanks, contributed to high-flowing rivers and flooding lakes.

By February, most heat was concentrated in the Antarctic Peninsula at the northernmost part of the continent. A new Antarctic maximum temperature of 18.4°C was recorded on February 6 at Argentina’s Esperanza research station on the Peninsula – almost 1°C above the previous record. Three days later this was eclipsed when 20.75°C was reported at Brazil’s Marambio station, on Seymour Island east of the Peninsula.

What caused the heatwave?

The pace of warming from global climate change has been generally slower in East Antarctica compared with West Antarctica and the Antarctic Peninsula. This is in part due to the ozone hole, which has occurred in spring over Antarctica since the late 1970s.

The hole has tended to strengthen jet stream winds over the Southern Ocean promoting a generally more ‘positive’ state of the Southern Annular Mode in summer. This means the Southern Ocean’s westerly wind belt has tended to stay close to Antarctica at that time of year creating a seasonal ‘shield’, reducing the transfer of warm air from the Earth’s temperate regions to Antarctica.




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But during the spring of 2019 a strong warming of the stratosphere over Antarctica significantly reduced the size of the ozone hole. This helped to support a more ‘negative’ state of the Southern Annular Mode and weakened the shield.

Other factors in late 2019 may have also helped to warm Antarctica. The Indian Ocean Dipole was in a strong ‘positive’ state due to a late retreat of the Indian monsoon. This meant that water in the western Indian Ocean was warmer than normal. Air rising from this and other warm ocean patches in the Pacific Ocean provided energy sources that altered the path of weather systems and helped to disturb and warm the stratosphere.

Is a warming Antarctica good or bad?

Localised flooding appeared to benefit some Vestfold Hills’ moss banks which were previously very drought-stressed. Prior to the flood event, most mosses were grey and moribund, but one month later many moss shoots were green.

Given the generally cold conditions of Antarctica, the warmth may have benefited the flora (mosses, lichens and two vascular plants), and microbes and invertebrates, but only where liquid water formed. Areas in the Vestfold Hills away from the flooding became more drought-stressed over the summer.

High temperatures may have caused heat stress in some organisms. Antarctic mosses and lichens are often dark in colour, allowing sunlight to be absorbed to create warm microclimates. This is a great strategy when temperatures are just above freezing, but heat stress can occur once 10°C is exceeded.

On King George Island, near the Antarctic Peninsula, our measurements showed that in January 2019 moss surface temperatures only exceeded 14°C for 3% of the time, but in 2020 this increased fourfold (to 12% of the time).

Based on our experience from previous anomalous hot Antarctic summers, we can expect many biological impacts, positive and negative, in coming years. The most recent event highlights the connectedness of our climate systems: from the surface to the stratosphere, and from the monsoon tropics to the southernmost continent.

Under climate change, extreme events are predicted to increase in frequency and severity, and Antarctica is not immune.




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The Conversation


Dana M Bergstrom, Principal Research Scientist, University of Wollongong; Andrew Klekociuk, Adjunct Senior Lecturer, University of Tasmania; Diana King, Research officer, University of Wollongong, and Sharon Robinson, Professor, University of Wollongong

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

I studied what happens to reef fish after coral bleaching. What I saw still makes me nauseous



Victor Huertas, Author provided

Jodie L. Rummer, James Cook University

The Great Barrier Reef is suffering its third mass bleaching event in five years. It follows the record-breaking mass bleaching event in 2016 that killed a third of Great Barrier Reef corals, immediately followed by another in 2017.

While we don’t know if fish populations declined from the 2016 bleaching disaster, one 2018 study did show the types of fish species on some coral reefs changed. Our study dug deeper into fish DNA.

I was part of an international team of scientists that, for the first time, tracked wild populations of five species of coral reef fish before, during, and after the 2016 marine heatwave.

From a scientific perspective, the results are fascinating and world-first.

Marine heatwaves are now becoming more frequent and more severe with climate change. Corals are bleaching, as pictured here.
Jodie Rummer, Author provided

We used gene expression as a tool to survey how well fish can handle hotter waters. Gene expression is the process where a gene is read by cell machinery and creates a product such as a protein, resulting in a physical trait.

We know many tropical coral reef fish are already living at temperatures close to their upper limits. Our findings can help predict which of these species will be most at risk from repeated heatwaves.




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But from a personal perspective, I still feel nauseous thinking about what the reef looked like during this project. I’ll probably feel this way for a long time.

Rewind to November 2015

We were prepared. Back then we didn’t know the reef was about to bleach and lead to widespread ecological devastation. But we did anticipate that 2016 would be an El Niño year. This is a natural climate cycle that would mean warm summer waters in early 2016 would stick around longer than usual.

But we can’t blame El Niño – the ocean has already warmed by 1°C above pre-industrial levels from continued greenhouse gas emissions. What’s more, marine heatwaves are becoming more frequent and severe with climate change.

Given this foresight, we took some quick liver biopsies from several coral reef fish species at our field site in December 2015, just in case.

Coral bleaching at Magnetic Island, March 2020.
Victor Huertas, Author provided

A couple months later, we were literally in hot water

In February 2016, my colleague and I were based on Lizard Island in the northern part of the Great Barrier Reef working on another project.

The low tides had shifted to the afternoon hours. We were collecting fish in the shallow lagoon off the research station, and our dive computers read that the water temperature was 33°C.




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We looked at each other. These are the temperatures we use to simulate climate change in our laboratory studies for the year 2050 or 2100, but they’re happening now.

Over the following week, we watched corals turn fluorescent and then bone-white.

The water was murky with slime from the corals’ immune responses and because they were slowly exuding their symbiotic zooxanthellae – the algae that provides corals with food and the vibrant colours we know and love when we think about a coral reef. The reef was literally dying before our eyes.

A third of the corals on the Great Barrier Reef perished after the 2016 heatwave.
Jodie Rummer, Author provided

Traits for dealing with heatwaves

We sampled fish during four time periods around this devastating event: before, at the start, during, and after.

Some genes are always “switched on”, regardless of environmental conditions. Other genes switch on or off as needed, depending on the environment.

If we found these fish couldn’t regulate their gene expression in response to temperature stress, then the functions – such as metabolism, respiration, and immune function – also cannot change as needed. Over time, this could compromise survival.




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The plasticity (a bit like flexibility) of these functions, or phenotypes, is what buffers an organism from environmental change. And right now, this may be the only hope for maintaining the health of coral reef ecosystems in the face of repeated heatwave events.

So, what were the fish doing?

We looked at expression patterns of thousands of genes. We found the same genes responded differently between species. In other words, some fish struggled more than others to cope with marine heatwaves.

Ostorhinchus doederleini, a species of cardinalfish, is bad at coping with marine heatwaves.
Göran Nilsson, Author provided

The species that coped the least was a nocturnal cardinalfish species (Cheilodipterus quinquelineatus). We found it had the lowest number of differentially expressed genes (genes that can switch on or off to handle different stressors), even when facing the substantial change in conditions from the hottest to the coolest months.

In contrast, the spiny damselfish (Acanthochromis polyacanthus) responded to the warmer conditions with changes in the expression of thousands of genes, suggesting it was making the most changes to cope with the heatwave conditions.

What can these data tell us?

Our findings not only have implications for specific fish species, but for the whole ecosystem. So policymakers and the fishing industry should screen more species to predict which will be sensitive and which will tolerate warming waters and heatwaves. This is not a “one size fits all” situation.

One of the species that showed the least amount of change under warming was Cheilodipterus quinquelineatus.
Moises Antonio Bernal de Leon, Author provided

Fish have been on the planet for more than 400 million years. Over time , they may adapt to rising temperatures or migrate to cooler waters.

But, the three recent mass bleaching events is unprecedented in human history, and fish won’t have time to adapt.




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My drive to protect the oceans began when I was a child. Now it’s my career. Despite the progress my colleagues and I have made, my nauseous feelings remain, knowing our science alone may not be enough to save the reef.

The future of the planet, the oceans, and the Great Barrier Reef lies in our collective actions to reduce global warming. What we do today will determine what the Great Barrier Reef looks like tomorrow.The Conversation

Jodie L. Rummer, Associate Professor & Principal Research Fellow, James Cook University

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

Here’s what the coronavirus pandemic can teach us about tackling climate change


Natasha Chassagne, University of Tasmania

Every aspect of our lives has been affected by the coronavirus. The global economy has slowed, people have retreated to their homes and thousands have died or become seriously ill.

At this frightening stage of the crisis, it’s difficult to focus on anything else. But as the International Agency has said, the effects of coronavirus are likely to be temporary but the other global emergency – climate change – is not.

Stopping the spread of coronavirus is paramount, but climate action must also continue. And we can draw many lessons and opportunities from the current health crisis when tackling planetary warming.

Action to reduce greenhouse gas emissions must not be compromised by the coronavirus pandemic.
EPA/MAST IRHAM

A ‘degrowing’ economy

S&P Global Ratings this week said measures to contain COVID-19 have pushed the global economy into recession.

Economic analyst Lauri Myllyvirta estimates the pandemic may have reduced global emissions by 200 megatonnes of carbon dioxide to date, as air travel grinds to a halt, factories close down and energy demand falls.

In the first four weeks of the pandemic, coal consumption in China alone fell by 36%, and oil refining capacity reduced by 34%.

In many ways, what we’re seeing now is a rapid and unplanned version of economic “degrowth” – the transition some academics and activists have for decades said is necessary to address climate change, and leave a habitable planet for future generations.




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Degrowth is a proposed slowing of growth in sectors that damage the environment, such as fossil fuel industries, until the economy operates within Earth’s limits. It is a voluntary, planned and equitable transition in developed nations which necessarily involves an increased focus on the environment, human well-being, and capabilities (good health, decent work, education, and a safe and healthy environment).

Such a transformation would be profound, and so far no nation has shown the will to implement it. It would require global economies to “decouple” from carbon to prevent climate-related crises. But the current unintended economic slowdown opens the door to such a transition, which would bring myriad benefits to the climate.

The idea of sustainable degrowth is very different to a recession. It involves scaling back environmentally damaging sectors of the economy, and strengthening others.

Reduced air travel is helping drive global emissions down.
James Gourley/AAP

A tale of two emergencies

Climate change has been declared a global emergency, yet to date the world has largely failed to address it. In contrast, the global policy response to the coronavirus emergency has been fast and furious.

There are several reasons for this dramatic difference. Climate change is a relatively slow-moving crisis, whereas coronavirus visibly escalates over days, even hours, increasing our perception of the risks involved. One thing that history teaches us about politics and the human condition in times of peril, we often take a “crisis management” approach to dealing with serious threats.




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As others have observed, the slow increase in global temperatures means humans can psychologically adjust as the situation worsens, making the problem seem less urgent and meaning people are less willing to accept drastic policy measures.

The human ability to adapt to climate change can make it seem less urgent.
CHAMILA KARUNARATHNE/EPA

Key lessons from coronavirus

The global response to the coronavirus crisis shows that governments can take immediate, radical emergency measures, which go beyond purely economic concerns, to protect the well-being of all.

Specifically, there are practical lessons and opportunities we can take away from the coronavirus emergency as we seek to tackle climate change:

Act early: The coronavirus pandemic shows the crucial importance of early action to prevent catastrophic consequences. Governments in Taiwan, South Korea and Singapore acted quickly to implement quarantine and screening measures, and have seen relatively small numbers of infections. Italy, on the other hand, whose government waited too long to act, is now the epicentre of the virus.




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Go slow, go local: Coronavirus has forced an immediate scale-down of how we travel and live. People are forging local connections, shopping locally, working from home and limiting consumption to what they need.

Researchers have identified that fears about personal well-being represent a major barrier to political support for the degrowth movement to date. However with social distancing expected to be in place for months, our scaled-down lives may become the “new normal”. Many people may realise that consumption and personal well-being are not inextricably linked.

Stimulus spending should be directed to clean energy.
EPA

New economic thinking is needed. A transition to sustainable degrowth can help. We need to shift global attention from GDP as an indicator of well-being, towards other measures that put people and the environment first, such as New Zealand’s well-being budget, Bhutan’s gross national happiness index, or Ecuador’s social philosophy of buen vivir (good living).

Spend on clean energy: The International Energy Agency (IEA) says clean energy should be “at the heart of stimulus plans to counter the coronavirus crisis”.

The IEA has called on governments to launch sustainable stimulus packages focused on clean energy technologies. It says hydrogen and carbon-capture also need major investment to bring them to scale, which could be helped by the current low interest rates.

Governments could also use coronavirus stimulus packages to reskill workers to service the new “green” economy, and address challenges in healthcare, sanitation, aged care, food security and education.

More people are shopping locally during the pandemic.
AAP/STEFAN POSTLES

Looking ahead

As climate scientist Katharine Hayhoe said this month:

What really matters is the same for all of us. It’s the health and safety of our friends, our family, our loved ones, our communities, our cities and our country. That’s what the coronavirus threatens, and that’s exactly what climate change does, too.

The coronavirus crisis is devastating, but failing to tackle climate change because of the pandemic only compounds the tragedy. Instead, we must draw on the lessons of coronavirus to address the climate challenge.The Conversation

Natasha Chassagne, University Associate, University of Tasmania, University of Tasmania

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

New ways of ‘being together apart’ can work for us and the planet long after coronavirus crisis passes


Random Thoughts

Oxfam/Wikimedia Commons, CC BY

Andrew Glover, RMIT University and Tania Lewis, RMIT University

Most major corporate, academic and other networking events have been cancelled because of the risks of spreading the coronavirus while travelling or at the events themselves. This flurry of cancellations has even spawned a literally titled website: https://www.isitcanceledyet.com/. But the changes in behaviour now being forced upon us might benefit the planet in the long term as we find and get used to other ways of holding meetings.

The COVID-19 pandemic is driving the development of these alternatives to physical travel and meetings much more strongly than climate change had to date. With many countries closing their borders, limiting domestic travel and imposing restrictions on large gatherings, few conferences are likely to proceed in the coming months of 2020.




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Snowy 2.0 is a wolf in sheep’s clothing – it will push carbon emissions up, not down



Luka Cochleae/AAP

Bruce Mountain, Victoria University

The massive Snowy 2.0 pumped hydro project is soon expected to be granted environmental approval. I and others have criticised the project on several grounds, including its questionable financial viability and overstated benefits to the electricity system. But Snowy 2.0’s greenhouse gas emissions have barely been discussed.

Both Snowy Hydro and its owner, the federal government, say the project will help expand renewable electricity generation (and by extension, contribute to emissions reduction from the energy sector).

However, closer inspection shows it won’t work that way. For at least the next couple of decades, Snowy 2.0 will store coal-fired electricity, not renewable electricity. In fact, I predict Snowy 2.0 will create additional demand for coal-fired generation and lead to an increase in greenhouse gas emissions for the foreseeable future.

Khancoban Dam, part of the soon-to-be expanded Snowy Hydro scheme.
Snowy Hydro Ltd

The problem explained

The expanded Snowy Hydro scheme in southern New South Wales will involve pumping water uphill to a reservoir, storing it, and then releasing it downhill to generate electricity when demand is high.

The emissions reduction potential of the project rests on what type of electricity is used to pump the water uphill. Snowy Hydro says it will pump the water when a lot of wind and solar energy is being produced (and therefore when wholesale electricity prices are low).

But the crucial point here is that wind and solar farms produce electricity whenever the resource is available. This will happen irrespective of whether Snowy 2.0 is producing or consuming energy.




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When Snowy 2.0 pumps water uphill to its upper reservoir, it adds to demand on the electricity system. The generators that will provide this extra electricity are the ones that would not operate unless Snowy 2.0’s pumping demand was calling them into operation.

These will not be renewable generators since they will be operating anyway. Rather, for the next couple of decades at least, coal-fired electricity generators – the next cheapest form of electricity after renewables – will provide Snowy 2.0’s power.

Snowy Hydro claims Snowy 2.0 will add 2000 megawatts of renewable capacity to the national electricity market. However Snowy 2.0 is a storage device, and its claim to be renewable rests on the source of the electricity that it stores and then reproduces. It is not renewable electricity that Snowy 2.0 will store and reproduce for the foreseeable future.

The Snowy 2.0 scheme will lead to more coal use in the foreseeable future.
Julian Smith/AAP

Why this matters

Ageing coal-fired generaters will account for a smaller share of Australia’s electricity production over time as they become uneconomic and close down. But projections from the Australian Energy Market Operator show coal will make up a significant proportion of electricity production for the next two decades.

It is only when all coal-fired generators have closed (and gas-fired generators have not taken their place) that Snowy 2.0 could claim to be using renewable electricity to power its pumps.

Does this matter? Yes, very much. Using Snowy Hydro’s projections of how much
electricity Snowy 2.0 will pump each year from 2025 to 2047 (the period over which they have developed their projections) I estimate that Snowy 2.0 will, on average, account for 5.4 million tonnes of carbon dioxide equivalent each year.




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This is clearly a big number – roughly equivalent to the annual greenhouse gas emissions of Australia’s mineral or chemical industry, and equal to the annual emissions of 2.4 million cars.

If we assume, conservatively, that emissions have a cost of A$20 per tonne of carbon, then Snowy 2.0 will impose an additional annual cost of A$108 million on the Australian community that will need to be countered by emissions reduction somewhere else in the economy.

Over 20 years, Snowy 2.0 will lead to more greenhouse gas emissions than three million cars.
Julian Smith/AAP

The NSW government has adopted a target of net-zero emissions by 2050. But using Snowy Hydro’s projections of pumped energy, average greenhouse gas emissions attributable to Snowy 2.0 over its first decade will increase NSW’s emissions by about 10% of their current levels each year.

This proportion will increase if the government successfully reduces emissions elsewhere.

Of course, emission reduction is not just an issue for the states. The federal
government has been at pains to affirm its commitment to the Paris climate accord. Snowy 2.0 will undermine the achievement of this commitment.

If additional energy storage is needed to stabilise our electricity grid, it can be provided by many alternatives with a much smaller greenhouse gas impact such as demand response, gas or diesel generators, batteries or smaller and more efficient pumped-hydro generators.

Meeting the climate challenge

Emissions associated with storage is given little attention in Australia but is well-researched overseas. Since Australia’s state and federal governments profess a commitment to reducing greenhouse gas emissions, this is a serious omission.




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Energy storage will increase emissions as long as fossil fuel generators dominate the power system.

In meeting the climate challenge, greenhouse gas emissions must become a more prominent consideration in the planning and approval of all electricity projects, including storage – and especially for Snowy 2.0.


In response the points raised in this article, Snowy Hydro said Snowy 2.0 would add 2,000 megawatts (MW) of renewable capacity to the national electricity market (NEM).

“In the absence of Snowy 2.0, the NEM will have to fill the capacity need with other power stations, which would inevitably be fossil-fuelled,” the company said in a statement.

“Snowy will sell capacity contracts (tantamount to insurance against NEM price volatility and spikes) to a range of NEM counterparties, as it does now and has done for decades.”

Snowy Hydro said Snowy 2.0 would directly draw wind and solar capacity into the NEM, via the contract market.

It said this market, rather than the wholesale market, drives investment and electricity generation.

“Snowy Hydro’s renewable energy procurement program, through which Snowy contracted with 888 MW of wind and solar facilities in 2019, has made the construction of eight new wind and solar projects possible,” Snowy Hydro said.

“In the NEM, what happens subsequently to the spot price is of little interest to the owners of these facilities, because their revenue is guaranteed through their offtake contracts with Snowy.”

The company said the energy produced by wind and solar plants, backed by Snowy’s existing large-scale generation fleet, was “the most cost-effective and reliable way to serve the customers of the NEM in the future.”

Snowy Hydro said Snowy 2.0 would pump water uphill using cheap electricity from wind and solar – often most plentiful when NEM prices are low – rather than expensive electricity from coal.

“The water is released when prices are high – this is one of the four Snowy 2.0 revenue streams,” it said.

“Given that Snowy has the water storage capability to pump when electricity prices are low, and generate when electricity prices are high, why would Snowy choose to buy expensive coal-fired energy to pump water uphill at times of high prices?”The Conversation

Bruce Mountain, Director, Victoria Energy Policy Centre, Victoria University

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

It’s official: the last five years were the warmest ever recorded


It’s official: the last five years were the warmest ever recorded

Blair Trewin, Australian Bureau of Meteorology and Pep Canadell, CSIRO

The World Meteorological Organisation today published a definitive climate report card showing concentrations of greenhouse gases continue to rise, and the last five years were the warmest on record.

The Statement on the State of the Global Climate also confirmed that the ongoing drought and recent bushfires in Australia were a globally significant climate event.

The report is an annual, comprehensive overview of the latest information from the world’s meteorological services and other key institutions. We are among the many authors who contributed.

It’s an important record of the magnitude and speed of changes to global climate, drawing on the latest data from across the fields of climate science.

A record year

Global average temperatures in 2019 were 1.1℃ above pre-industrial levels. Only 2016 was hotter, but that year came at the end of an extreme El Niño, which typically has a warming influence on global temperatures.

The last five years were the world’s five warmest on record. Areas which were especially warm, with temperatures in 2019 more than 2℃ above average, included parts of Australia, Alaska and northern Russia, eastern Europe and southern Africa. Central North America was the only significant land area with below-average temperatures.


CC BY-ND

Human-driven climate change is predominantly caused by increasing greenhouse gases in the atmosphere. Concentrations of carbon dioxide, methane and nitrous oxide, the three most potent greenhouse gases, have continued to grow and are now, respectively, 147%, 259% and 123% of pre-industrial levels, measured in the year 1750.

Global emissions of carbon dioxide from fossil fuels reached a record high of 36.6 billion tonnes, of which about half is absorbed by vegetation and oceans.

The Antarctic ozone hole was its smallest since 2002, after an unusually early spring breakdown of the Antarctic polar vortex following a sudden warming in the polar stratosphere.




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


Many other indicators of large-scale climate change continued their long-term trends in 2019. These include the heat content of the global ocean – an important indicator because around 90% of warming generated by greenhouse gases from human activities is taken by the oceans.

In 2019, ocean heat content reached the highest levels since instrumental records began. Global mean sea level also reached new highs in 2019, while Arctic and Antarctic sea ice extent was well below average.

Glacial mass declined for the 32nd consecutive year. In Switzerland, for example, glacier loss over the past five years has exceeded 10%, the highest rate of decline in more than a century.


CC BY-ND

Australia’s fire and drought

The report confirms the ongoing drought in Australia and exceptional fire weather conditions late in the year were among the most significant global climate events last year.

2019 was Australia’s warmest and driest year since national records began – the first time both records have been broken in the same year.


CC BY-ND

In December, the monthly accumulated Forest Fire Danger Index – an indicator of severe fire weather – was the highest on record for any month in Queensland, New South Wales, South Australia and the ACT. Some fires burned for longer than two months.

In January and February 2019, a dry summer in Tasmania contributed to fires in the normally moist western and central parts of the island – the second time in four years that fires burnt regions where historically such events were extremely rare.




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The drought was strongly influenced by a very strong positive phase of the Indian Ocean Dipole – an oscillation of sea surface temperatures which affects the climate in Australia. A strong negative Southern Annular Mode – a climate driver which originates in Antarctica – brought westerly winds and dry conditions to the eastern states from September.

Australia was not the only nation affected by drought in 2019 – southern Africa, southeast Asia and central Chile were also significantly affected. In the Chilean capital Santiago, rainfall was more than 70% below average.

Heatwaves and cyclones

Two exceptional heatwaves affected Europe in the summer. France, Germany, Belgium, the Netherlands and the United Kingdom all had their highest recorded temperatures. Belgium and the Netherlands both reached 40℃ for the first time, and Paris reached a high of 42.6℃.

Australia had extreme heatwaves both early and late in the year, and in South America, temperatures exceeded 30℃ as far south as Tierra del Fuego.




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Tropical cyclones are amongst the most destructive weather phenomena in most years, and 2019 was no exception. The most severe cyclone impact was in Mozambique and Zimbabwe, when Cyclone Idai hit in mid-March, killing more than 900 people.

Hurricane Dorian, one of the strongest ever to affect land in the North Atlantic, caused massive destruction in the Bahamas, whilst Typhoon Hagibis led to exceptional flooding in Japan, and daily rainfall of more than 900 millimetres. The North Indian Ocean also had its most active cyclone season on record.

Looking to the future

Global climate projections show that under all scenarios, temperatures will continue to warm – and years such as 2019 will become the norm this decade.

The report is intended to inform decisions around the world on adaptation to, and mitigation of, climate change.The Conversation

Blair Trewin, Climate scientist, Australian Bureau of Meteorology and Pep Canadell, Chief research scientist, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO

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

A rare natural phenomenon brings severe drought to Australia. Climate change is making it more common



Shutterstock

Nicky Wright, Australian National University; Bethany Ellis, Australian National University, and Nerilie Abram, Australian National University

Weather-wise, 2019 was a crazy way to end a decade. Fires spread through much of southeast Australia, fuelled by dry vegetation from the ongoing drought and fanned by hot, windy fire weather.

On the other side of the Indian Ocean, torrential rainfall and flooding devastated parts of eastern Africa. Communities there now face a locust plague and food shortages.

These intense events can partly be blamed on the extreme positive Indian Ocean Dipole, a climate phenomenon that unfolded in the second half of 2019.




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The Indian Ocean Dipole refers to the difference in sea surface temperature on either side of the Indian Ocean, which alters rainfall patterns in Australia and other nations in the region. The dipole is a lesser-known relative of the Pacific Ocean’s El Niño.

Climate drivers, such as the Indian Ocean Dipole, are an entirely natural phenomenon, but climate change is modifying the behaviour of these climate modes.

In research published today in Nature, we reconstructed Indian Ocean Dipole variability over the last millennium. We found “extreme positive” Indian Ocean Dipole events like last year’s are historically very rare, but becoming more common due to human-caused climate change. This is big news for a planet already struggling to contain global warming.

So what does this new side-effect of climate change mean for the future?

The Indian Ocean brings drought and flooding rain

First, let’s explore what a “positive” and “negative” Indian Ocean Dipole means.

During a “positive” Indian Ocean Dipole event, waters in the eastern Indian Ocean become cooler than normal, while waters in the western Indian Ocean become warmer than normal.

Warmer water causes rising warm, moist air, bringing intense rainfall and flooding to east Africa. At the same time, atmospheric moisture is reduced over the cool waters of the eastern Indian Ocean. This turns off one of Australia’s important rainfall sources.




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In fact, over the past century, positive Indian Ocean Dipoles have led to the worst droughts and bushfires in southeast Australia.

The Indian Ocean Dipole also has a negative phase, which is important to bring drought-breaking rain to Australia. But the positive phase is much stronger and has more intense climate impacts.

We’ve experienced extreme positive Indian Ocean Dipole events before. Reliable instrumental records of the phenomenon began in 1958, and since then a string of very strong positive Indian Ocean Dipoles have occurred in 1961, 1994, 1997 and now 2019.

The Dipole Mode Index is used to track variability of the Indian Ocean Dipole.
Author provided

But this instrumental record is very short, and it’s tainted by the external influence of climate change.

This means it’s impossible to tell from instrumental records alone how extreme Indian Ocean Dipoles can be, and whether human-caused climate change is influencing the phenomenon.

Diving into the past with corals

To uncover just how the Indian Ocean Dipole has changed, we looked back through the last millennium using natural records: “cores” taken from nine coral skeletons (one modern, eight fossilised).

These coral samples were collected just off of Sumatra, Indonesia, so they’re perfectly located for us to reconstruct the distinct ocean cooling that characterises positive Indian Ocean Dipole events.

Scientists drilling into corals to study past climate. Corals are like trees, and grow a band for every year they live.
Jason Turl, Author provided

Corals grow a lot like trees. For every year they live they produce a growth band, and individual corals can live for more than 100 years. Measuring the oxygen in these growth bands gives us a detailed history of the water temperature the coral grew in, and the amount of rainfall over the reef.

In other words, the signature of extreme events like past positive Indian Ocean Dipoles is written in the coral skeleton.

Altogether, our coral-based reconstruction of the Indian Ocean Dipole spans 500 years between 1240 and 2019. There are gaps in the timeline, but we have the best picture so far of how exactly the Indian Ocean Dipole has varied in the past.

How unusual was the 2019 Indian Ocean Dipole event?

Extreme events like the 2019 Indian Ocean Dipole have historically been very rare.

We found only ten extreme positive Indian Ocean Dipole events in the entire record. Four occurred in the past 60 years, but only six occurred in the remaining 440 years before then. This adds more weight to evidence that positive Indian Ocean Dipole events have been occurring more often in recent decades, and becoming more intense.




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But another finding from the reconstruction surprised – and worried – us. Events like 2019 aren’t the worst of what the Indian Ocean Dipole can throw at us.

Of the extreme events we found in our reconstruction, one of them, in 1675, was much stronger than anything we’ve seen in observations from the last 60 years.

The 1675 event was around 30–40% stronger than what we saw in 1997 (around the same magnitude as 2019). Historical accounts from Asia show this event was disastrous, and the severe drought it caused led to crop failures, widespread famine and mortality, and incited war.

The wiggles that make up 500 years of reconstructed Indian Ocean Dipole variability. The red triangles show when extreme positive events occurred.
Author provided

As far as we can tell, this event shows just how extreme Indian Ocean Dipole variability can be, even without any additional prompting from external forces like human-caused climate change.

Why should we care?

Indian Ocean Dipole variability will continue to episodically bring extreme climate conditions to our region.

Drilling through fossilised coral layers to look into the past.
Nerilie Abram, Author provided

But previous studies, as well as ours, have shown human-caused climate change has shortened the gaps between these episodes, and this trend will continue. This is because climate change is causing the western side of the Indian Ocean to warm faster than in the east, making it easier for positive Indian Ocean Dipole events to establish.

In other words, drought-causing positive Indian Ocean Dipole events will become more frequent as our climate continues to warm.

In fact, climate model projections indicate extreme positive Indian Ocean Dipole events will occur three times more often this century than last, if high greenhouse gas emissions continue.




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This means events like last year will almost certainly unfold again soon, and we’re upping the odds of even worse events that, through the fossil coral data, we now know are possible.

Knowing we haven’t yet seen the worst of the Indian Ocean Dipole is important in planning for future climate risks. Future extremes from the Indian Ocean will act on top of long-term warming, giving a double-whammy effect to their impacts in Australia, like the record-breaking heat and drought of 2019.

But perhaps most importantly, rapidly cutting greenhouse gas emissions will limit how often positive Indian Ocean Dipole events occur in future.The Conversation

Nicky Wright, Research Fellow, Australian National University; Bethany Ellis, PhD Candidate, Australian National University, and Nerilie Abram, Professor; ARC Future Fellow; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University

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