El Niño has rapidly become stronger and stranger, according to coral records

Mandy Freund, University of Melbourne; Ben Henley, University of Melbourne; David Karoly, CSIRO; Helen McGregor, University of Wollongong, and Nerilie Abram, Australian National University

The pattern of El Niño has changed dramatically in recent years, according to the first seasonal record distinguishing different types of El Niño events over the last 400 years.

A new category of El Niño has become far more prevalent in the last few decades than at any time in the past four centuries. Over the same period, traditional El Niño events have become more intense.

This new finding will arguably alter our understanding of the El Niño phenomenon. Changes to El Niño will influence patterns of precipitation and temperature extremes in Australia, Southeast Asia and the Americas.

Some climate model studies suggest this recent change in El Niño “flavours” could be due to climate change, but until now, long-term observations were limited.

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Read more:
Explainer: El Niño and La Niña

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Our paper, published in Nature Geoscience today, fills this gap using coral records to reconstruct El Niño event types for the past 400 years.

Central Pacific El Niño event frequency relative to Eastern Pacific El Niño event frequency over the past four centuries, expressed as the number of events in 30-year sliding windows.
Author provided

What is El Niño?

El Niño describes an almost year-long warming of the surface ocean in the tropical Pacific. These warming events are so extreme and powerful that their impacts are felt around the globe.

During strong El Niño events, Australia and parts of Asia often receive much less rainfall than during normal years. The opposite applies to the western parts of the Americas, where the stronger rising motion over unusually warm ocean waters often results in heavy rainfall, causing massive floods. At the same time many of the hottest years on record across the globe coincide with El Niño events.

El Niño and its global impacts. Schematic of idealised atmospheric and sea surface temperature conditions during Central (top left) and Eastern Pacific events (top right). Annual global temperature anomalies (lower panel) show the familiar upward trend due to climate change. Many of the hottest years on record coincide with El Niño events.
NOAA National Centers for Environmental information, Climate at a Glance: Global Time Series

The reason for such far-reaching influences on weather is the changes El Niño causes in atmospheric circulation. In normal years, a massive circulation cell, called the Walker circulation, moves air along the equator across the tropical Pacific.

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Read more:
500 years of drought and flood: trees and corals reveal Australia’s climate history

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Warmer waters during El Niño events disrupt or even reverse this circulation pattern. The type of atmospheric disruption and the climate impacts this causes depend in particular on where the warm waters of El Niño are located.

The new ‘flavour’ of El Niño

A new “flavour” of El Niño is now recognised in the tropical Pacific. This type of El Niño is characterised by warm ocean temperatures in the Central Pacific, rather than the more typical warming in the far Eastern Pacific near the South American coast, some 10,000km away.

Although not as strong as the Eastern Pacific version, the Central Pacific El Niño is clearly observed in recent decades, including in 2014-15 and most recently in 2018-19. Over most of the last 400 years, El Niño events happened roughly at the same rate in the Central and Eastern Pacific.

Differences between Central and Eastern Pacific El Niño events and their associated drought impacts.

By the end of the 20th century, though, our research shows a sudden change: a sharp increase of Central Pacific El Niño events becomes evident. At the same time, the number of conventional Eastern Pacific events stayed relatively low, but the three most recent Eastern-type events (in 1982-83, 1997-98 and 2015-16) were unusually strong.

Using coral to unlock the past

Our understanding of the new Central Pacific flavour of El Niño is hindered by the fact that El Niño events happen only every 2-7 years. So during our lifetime we can observe only a handful of events.

This isn’t enough to really understand Central Pacific El Niño, and whether they are becoming more common.

That’s why we look at corals from the tropical Pacific. The corals started growing decades to centuries before we began routinely measuring the climate with instruments. The corals are an excellent archive of changes in water conditions they experience as they grow, including ocean changes related to El Niño. We combined the information from a network of coral records that preserve seasonal histories.

At a seasonal timescale, we can see the characteristic patterns of past El Niño events in the chemistry of the corals. These patterns tell us which El Niño is which over the last 400 years. It is in this continuous picture of past El Niños obtained from coral archives that we found a clear picture of an unusual recent change in the Pacific’s El Niño flavours.

Underwater drilling of corals off Christmas Island (underwater team: Jennie Mallela, Oscar Branson; surface team: Jessica Hargreaves, Nerilie Abram).
Jason Turl, Nerilie Abram

Why do we care?

This extraordinary change in El Niño behaviour has serious implications for societies and ecosystems around the world. For example, the most recent Eastern-Pacific El Niño event in 2015-2016 triggered disease outbreaks across the globe. With the impacts of climate change continuing to unfold, many of the hottest years on record also coincide with El Niño events.

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Read more:
Australia moves to El Niño alert and the drought is likely to continue

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What’s more, the Pacific Ocean is currently lingering in an El Niño state. With these confounding events, many people around the world are wondering what extreme weather will be inflicted upon them in the months and years to come.

Our new record opens a door to understanding past changes of El Niño, with implications for the future too. Knowing how the different types of El Niño have unfolded in the past will mean we are better able to model, predict and plan for future El Niños and their widespread impacts.

Mandy Freund, PhD Researcher, University of Melbourne; Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne; David Karoly, Leader, NESP Earth Systems and Climate Change Hub, CSIRO; Helen McGregor, ARC Future Fellow, University of Wollongong, and Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; 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.

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Summer forecast: scorching heat and heightened bushfire risk

Catherine Ganter, Australian Bureau of Meteorology

Large parts of Australia are facing a hotter and drier summer than average, according to the Bureau of Meteorology’s summer outlook.

Drier than average conditions are likely for much of northern Australia. Most of the country has at least an 80% chance of experiencing warmer than average day and night-time temperatures.

The threat of bushfire will remain high, with few signs of the sustained rain needed to reduce fire risk or make a significant dent in the ongoing drought.

Expect extreme heat

Large parts of Western Australia, most of Queensland and the Top End of the Northern Territory are expected to be drier than usual. Further south, the rest of the country shows no strong push towards a wetter or drier than average summer, which is a change for parts of the southeast compared to recent months.

Bureau of Meteorology

Queensland has already seen some extraordinary record-breaking heat in recent days, with summer yet to truly begin. With the summer outlook predicting warmer days and nights, combined with recent dry conditions and our long-term trend of increasing temperatures, some extreme highs are likely this summer.

Bureau of Meteorology

All of this means above-normal bushfire potential in eastern Australia, across New South Wales, Victoria and Queensland. The bushfire outlook, also released today, notes that rain in areas of eastern Australia during spring, while welcome, was not enough to recover from the long-term dry conditions. The current wet conditions across parts of coastal New South Wales will help, but it will not take long once hot and dry conditions return for vegetation to dry out.

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Read more:
Sydney storms could be making the Queensland fires worse

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What about El Niño?

The Bureau is currently at El Niño ALERT, which means a roughly 70% chance of El Niño developing this season.

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Read more:
Australia moves to El Niño alert and the drought is likely to continue

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However, not all the ducks are lined up. While ocean temperatures have already warmed to El Niño levels, to declare a proper “event” there must also be a corresponding response in the atmosphere to reinforce the ocean – this hasn’t happened yet.

That said, climate models expect this event to arrive in the coming months. The outlook has factored in that chance, and the conditions predicted are largely consistent with what we would expect during El Niño. In summer, this includes drier weather in parts of northern Australia, and warmer summer days.

Once an El Niño is in place, weather systems across southern Australia tend to be more mobile. This can mean shorter but more intense heatwaves in Victoria and southern South Australia. However, in New South Wales and Queensland, El Niño is associated with both longer and more intense heat waves.

The exact reason why the states are affected differently is complicated, but relates to the fast-moving cold fronts and troughs that sweep through Victoria and South Australia in the summertime, creating cool changes. These weather systems don’t influence areas further north so when hot air arrives, it takes longer to clear.

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Read more:
Drought, wind and heat: when fire seasons start earlier and last longer

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The heavy rains seen in parts of eastern Australia in October and November have provided some welcome short-term relief to drought-stricken farmers, but longer-term rainfall relief has not arrived yet. If El Niño arrives, this widespread relief may only be on the cards in autumn.

Catherine Ganter, Senior Climatologist, Australian Bureau of Meteorology

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

Will the arrival of El Niño mean fewer mosquitoes this summer?

A hot summer will mean wetlands dry out faster than ever, so how will pest mosquitoes respond?
Cameron Webb (NSW Health Pathology), Author provided

Cameron Webb, University of Sydney

Once the warm weather arrives, you know mosquitoes won’t be far behind. Spring heatwaves associated with the impending arrival of El Niño to the east coast of Australia may mean we’ll get an early taste of summer, but what about mosquitoes? Does a long, hot summer mean fewer annoying buzzing and biting beasts bothering us whenever we spend time outdoors?

Where do mosquitoes come from?

Mosquitoes are complex animals. Like all insects, they thrive in warm weather, but they need more than just heat, they need water.

Mosquitoes lay their eggs on or around water. Without it, they cannot complete their life cycle. Mosquito “wrigglers” hatch out from eggs and spend a week or so swimming about before emerging and flying off in search of blood. Depending on where the water is, whether it is wetlands, puddles or water-filled containers, different kinds of mosquitoes will be present.

There are hundreds of different mosquitoes in Australia. Some like salty water, some like fresh. Some need pristine conditions while some will tolerate filthy water trapped at the bottom of a septic tank.

Because mosquitoes rely on water, rainfall plays a critical role in determining how many mosquitoes will be buzzing about this summer.

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Read more:
Health Check: why mosquitoes seem to bite some people more

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A hot, dry summer must mean fewer mosquitoes?

The likelihood that an El Niño will bring drier and warmer conditions to eastern Australia this summer is increasing. The latest predictions from the Bureau of Meteorology are that there is a 70% chance an El Nino will occur this year, about three times more than usual.

At first, this may seem like good news for those averse to mosquito bites, but don’t pack away the repellent just yet.

While floods bring mosquitoes, and often outbreaks of mosquito-borne disease, drought will knock out almost all mosquitoes. It is true that the ongoing dry conditions across inland areas of Australia will ensure mosquito populations remain low, but that doesn’t mean mosquitoes will disappear completely.

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Read more:
The worst year for mosquitoes ever? Here’s how we find out

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Water doesn’t just come from rain

While a lack of rain will keep many wetlands dry, that isn’t the case for our coastal wetlands. Some of the worst pest mosquitoes in Australia are found in our mangroves, saltmarshes and sedgelands.

Mosquitoes, like the saltmarsh mosquito, Aedes vigilax, love wetlands regularly flooded by high tides. The eggs of this mosquito, laid in moist wetland mud, survive long periods of dry conditions. Once covered by tides, these hatch, complete development within a week, and emerge in extraordinary numbers to fly kilometres away into nearby communities to bite and spread disease-causing pathogens such as Ross River virus.

Not only have these mosquitoes found a way to survive without rain, they thrive in hot and dry conditions. Without substantial rainfall, the pools and ponds in the wetlands dry completely, killing off any fish or other aquatic predators, ensuring perfect conditions once the next series of tides comes flooding in. The arrival of El Niño may be bad news for lots of wetland wildlife, but it isn’t all bad news for mosquitoes.

The saltmarsh mosquito, Aedes vigilax, is one of the most important pest mosquitoes in coastal regions of Australia and has adapted to thrive in hot and dry conditions.
Stephen Doggett (NSW Health Pathology)

Bringing mosquitoes home

Much has been made of the impact of heatwaves on human health. It may also inadvertently increase health risks in metropolitan regions of Australia. A shortage of water increases the need to conserve and store water around the backyard. Unfortunately, that also means creating a home for mosquitoes.

One of the most widespread mosquitoes in the country, a mosquito that has probably bitten almost every Australian, is the backyard mosquito Aedes notoscriptus. This mosquito is found in water-filled containers around the backyard, from drains and roof gutters to rainwater tanks and bird baths. While you’d think hot and dry conditions will impact this mosquito, think about the extra effort we’re taking to store water around the home. If your rainwater tank isn’t properly screened or you’re keeping uncovered bins and buckets around the backyard filled with water, you’ll be providing a home for mosquitoes.

The debate about the impact of a changing climate on mosquitoes and mosquito-borne disease often focuses on the spread of tropical diseases into warming temperate regions. The truth is it may be the way humans respond to a changing climate through water-saving measures around the home that could increase mosquito impacts in urban areas. This also may bring a risk of exotic mosquitoes to our suburbs, which could transmit more serious mosquito-borne pathogens such as dengue, chikungunya and Zika viruses.

While some parts of Australia will have fewer annoying mozzies this summer, don’t be complacent about taking steps to avoid mosquito bites. Choose and use the right insect repellents and reduce opportunities for mosquitoes to move into your backyard by covering up water-holding containers.

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

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

Australia: El Nino

El Niño in the Pacific has an impact on dolphins over in Western Australia

Leaping bottlenose dolphins.
Kate Sprogis/MUCRU, Author provided

Kate Sprogis, Murdoch University; Fredrik Christiansen, Murdoch University; Lars Bejder, Murdoch University, and Moritz Wandres, University of Western Australia

Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a regular sight in the waters around Australia, including the Bunbury area in Western Australia where they attract tourists.

The dolphin population here, about 180km south of Perth, has been studied quite intensively since 2007 by the Murdoch University Cetacean Unit. We know the dolphins here have seasonal patterns of abundance, with highs in summer/autumn (the breeding season) and lows in winter/spring.

But in winter 2009, the dolphin population fell by more than half.

A leaping bottlenose dolphin.
Kate Sprogis/MUCRU, Author provided

This decrease in numbers in WA could be linked to an El Niño event that originated far away in the Pacific Ocean, we suggest in a paper published today in Global Change Biology. The findings could have implications for future sudden drops in dolphin numbers here and elsewhere.

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Read more: Tackling the kraken: unique dolphin strategy delivers dangerous octopus for dinner

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A Pacific event

The El Niño Southern Oscillation (ENSO) results from an interaction between the atmosphere and the tropical Pacific Ocean. ENSO periodically fluctuates between three phases: La Niña, Neutral and El Niño.

During our study from 2007 to 2013, there were three La Niña events. There was one El Niño event in 2009, with the initial phase in winter being the strongest across Australia.

The blue vertical line shows the decline in dolphin numbers (d) during the 2009 El Niño event.
Kate Sprogis, Author provided

Coupled with El Niño, there was a weakening of the Leeuwin Current, the dominant ocean current off WA. There was also a decrease in sea surface temperature and above average rainfall.

ENSO is known to affect the strength of the south-ward flowing Leeuwin Current.

During La Niña, easterly trade winds pile warm water on the western side of the Pacific Ocean. This westerly flow of warm water across the top of Australia through the Indonesian Throughflow results in a stronger Leeuwin Current.

During El Niño, trade winds weaken or reverse and the pool of warm water in the Pacific Ocean gathers on the eastern side of the Pacific Ocean. This results in a weaker Indonesian Throughflow across the top of Australia and a weakening in strength of the Leeuwin Current.

A chart showing sea surface temperature (SST) anomalies off Western Australia. Note the extremes for the moderate El Niño in 2009 (blue rectangle), and the strong La Niña in 2011 (red rectangle)
Moritz Wandres, Author provided

The strength and variability of the Leeuwin Current coupled with ENSO affects species biology and ecology in WA waters. This includes the distribution of fish species, the transport of rock lobster larvae, the seasonal migration of whale sharks and even seabird breeding success.

The question we asked then was whether ENSO could affect dolphin abundance?

What happened during the El Niño?

These El Niño associated conditions may have affected the distribution of dolphin prey, resulting in the movement of dolphins out of the study area in search of adequate prey elsewhere.

A surfacing bottlenose dolphin.
Kate Sprogis/MUCRU, Author provided

This is similar to what happens for seabirds in WA. During an El Niño event with a weakened Leeuwin Current, the distribution of prey changes around seabird’s breeding colonies resulting in a lower abundance of important prey species, such as salmon.

This in turn negatively impacts seabirds, including a decrease in reproductive output and changes in foraging.

In southwestern Australia, the amount of rainfall is strongly connected to sea surface temperature. When the water temperature in the Indian Ocean decreases, the region receives higher rainfall during winter.

High levels of rainfall contribute to terrestrial runoff and alters freshwater inputs into rivers and estuaries. The changes in salinity influences the distribution and abundance of dolphin prey.

This is particularly the case for the river, estuary, inlet and bay around Bunbury. Rapid changes in salinity during the onset of El Niño may have affected the abundance and distribution of fish species.

In 2009, there was also a peak in strandings of dead bottlenose dolphins in WA (between 1981-2010), but the cause of this remains unknown.

Of these strandings, in southwest Australia, there was a peak in June that coincided with the onset of the 2009 El Niño.

Specifically, in the Swan River, Perth, there were several dolphin deaths, with some resident dolphins that developed fatal skin lesions that were enhanced by the low-salinity waters.

What does all this mean?

Our study is the first to describe the effects of climate variability on a coastal, resident dolphin population.

A group of bottlenose dolphins.
Kate Sprogis/MUCRU, Author provided

We suggest that the decline in dolphin abundance during the El Niño event was temporary. The dolphins may have moved out of the study area due to changes in prey availability and/or potentially unfavourable water quality conditions in certain areas (such as the river and estuary).

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Read more: Explainer: El Niño and La Niña

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Long-term, time-series datasets are required to detect these biological responses to anomalous climate conditions. But few long-term datasets with data collected year-round for cetaceans (whales, dolphins and porpoises) are available because of logistical difficulties and financial costs.

Continued long-term monitoring of dolphin populations is important as climate models provide evidence for the doubling in frequency of extreme El Niño events (from one event every 20 years to one event every ten years) due to global warming.

With a projected global increase in frequency and intensity of extreme weather events (such as floods, cyclones), coastal dolphins may not only have to contend with increasing coastal human-related activities (vessel disturbance, entanglement in fishing gear, and coastal development), but also have to adapt to large-scale climatic changes.

Kate Sprogis, Research associate, Murdoch University; Fredrik Christiansen, Postdoctoral Research Fellow, Murdoch University; Lars Bejder, Professor, Cetacean Research Unit, Murdoch University, Murdoch University, and Moritz Wandres, Oceanographer PhD Student, University of Western Australia

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

Meet El Niño’s cranky uncle that could send global warming into hyperdrive

Ben Henley, University of Melbourne; Andrew King, University of Melbourne; Chris Folland, Met Office Hadley Centre; David Karoly, University of Melbourne; Jaci Brown, CSIRO, and Mandy Freund, University of Melbourne

You’ve probably heard about El Niño, the climate system that brings dry and often hotter weather to Australia over summer.

You might also know that climate change is likely to intensify drought conditions, which is one of the reasons climate scientists keep talking about the desperate need to reduce greenhouse gas emissions, and the damaging consequences if we don’t.

El Niño is driven by changes in the Pacific Ocean, and shifts around with its opposite, La Niña, every 2-7 years, in a cycle known as the El Niño Southern Oscillation or ENSO.

But that’s only part of the story. There’s another important piece of nature’s puzzle in the Pacific Ocean that isn’t often discussed.

It’s called the Interdecadal Pacific Oscillation, or IPO, a name coined by a study which examined how Australia’s rainfall, temperature, river flow and crop yields changed over decades.

Since El Niño means “the boy” in Spanish, and La Niña “the girl”, we could call the warm phase of the IPO “El Tío” (the uncle) and the negative phase “La Tía” (the auntie).

These erratic relatives are hard to predict. El Tío and La Tía phases have been compared to a stumbling drunk. And honestly, can anyone predict what a drunk uncle will say at a family gathering?

What is El Tío?

Like ENSO, the IPO is related to the movement of warm water around the Pacific Ocean. Begrudgingly, it shifts its enormous backside around the great Pacific bathtub every 10-30 years, much longer than the 2-7 years of ENSO.

The IPO’s pattern is similar to ENSO, which has led climate scientists to think that the two are strongly linked. But the IPO operates on much longer timescales.

We don’t yet have conclusive knowledge of whether the IPO is a specific climate mechanism, and there is a strong school of thought which proposes that it is a combination of several different mechanisms in the ocean and the atmosphere.

Despite these mysteries, we know that the IPO had an influence on the global warming “hiatus” – the apparent slowdown in global temperature increases over the early 2000s.

Global temperatures are on the up, but the IPO affects the rate of warming.
Author provided, data from NOAA, adapted from England et al. (2014) Nat. Clim. Change

Temperamental relatives

When it comes to global temperatures we know that our greenhouse gas emissions since the industrial revolution are the primary driver of the strong warming of the planet. But how do El Tío and La Tía affect our weather and climate from year to year and decade to decade?

Superimposed on top of the familiar long-term rise in global temperatures are some natural bumps in the road. When you’re hiking up a massive mountain, there are a few dips and hills along the way.

Several recent studies have shown that the IPO phases, El Tío and La Tía, have a temporary warming and cooling influence on the planet.

Rainfall around the world is also affected by El Tío and La Tía, including impacts such as floods and drought in the United States, China, Australia and New Zealand.

In the negative phase of the IPO (La Tía) the surface temperatures of the Pacific Ocean are cooler than usual near the equator and warmer than usual away from the equator.

Since about the year 2000, some of the excess heat trapped by greenhouse gases has been getting buried in the deep Pacific Ocean, leading to a slowdown in global warming over about the last 15 years. It appears as though we have a kind auntie, La Tía perhaps, who has been cushioning the blow of global warming. For the time being, anyway.

The flip side of our kind auntie is our bad-tempered uncle, El Tío. He is partly responsible for periods of accelerated warming, like the period from the late 1970s to the late 1990s.

The IPO has been in its “kind auntie” phase for well over a decade now. But the IPO could be about to flip over to El Tío. If that happens, it is not good news for global temperatures – they will accelerate upwards.

Models getting better

One of the challenges to climate science is to understand how the next decade, and the next couple of decades, will unravel. The people who look after our water and our environment want to know things like how fast our planet will warm in the next 10 years, and whether we will have major droughts and floods.

To do this we can use computer models of Earth’s climate. In our recently published paper in Environmental Research Letters, we evaluated how well a large number of models from around the world simulate the IPO. We found that the models do surprisingly well on some points, but don’t quite simulate the same degree of slow movement (the stubborn behaviour) of El Tío and La Tía that we observe in the real world.

But some climate models are better at simulating El Tío and La Tía. This is useful because it points the way to better models that could be used to understand the next few decades of El Tío, La Tía and climate change.

However, more work needs to be done to predict the next shift in the IPO and climate change. This is the topic of a new set of experiments that are going to be part the next round of climate model comparisons.

With further model development and new observations of the deep ocean available since 2005, scientists will be able to more easily answer some of these important questions.

Whatever the case, cranky old El Tío is waiting just around the corner. His big stick is poised, ready to give us a massive hiding: a swift rise in global temperatures over the coming decades.

And like a big smack, that would be no laughing matter.

Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne; Andrew King, Climate Extremes Research Fellow, University of Melbourne; Chris Folland, Science Fellow, Met Office Hadley Centre; David Karoly, Professor of Atmospheric Science, University of Melbourne; Jaci Brown, Senior Research Scientist, CSIRO, and Mandy Freund, PhD student, University of Melbourne

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

Australia simmers through hottest autumn on record

Andrew King, University of Melbourne

It’s the same old story: with 2016 on track to become the hottest year on record globally, and record-breaking heat already evident around the world, Australia has just experienced its hottest autumn on record.

Figures from the Bureau of Meteorology indicate Australia has experienced its hottest autumn on record.
Bureau of Meteorology

The Bureau of Meteorology has reported that for average temperatures across Australia, this has been the hottest March-May period ever recorded – beating the previous record, set in 2005, by more than 0.2℃.

Within this period, March was also the hottest on record, while April and May were each the second-warmest in a series extending back to 1910.

Temperatures were well above average across much of the country, especially in the east.
Bureau of Meteorology

Why so hot?

El Niño events tend to cause warmer weather across the east and north of Australia and the major El Niño of 2015-16 undoubtedly contributed to the extreme temperatures experienced across these areas.

However, climate change also played a significant role in our warmest autumn. Previous work, led by ANU climatologist Sophie Lewis, indicates that the human influence on the climate has made a record-breakingly hot autumn roughly 20 times more likely.

In other words, without climate change we would be much less likely to experience autumns as warm as this one has been in Australia.

How we’ll remember autumn 2016

In the past few months, Australia has seen many extreme hot weather events. Melbourne experienced its warmest March night on record, while Sydney had a run of 39 days with daytime highs above 26℃, as the summer heat continued long into March.

But it’s the coral bleaching event on the Great Barrier Reef that will likely linger in our memories the longest. Some 93% of the reef was found to be affected by bleaching and recent surveys have revealed that more than one-third of coral in the northern and central parts of the reef have died.

Without climate change, a bleaching event like this would be virtually impossible.

The extreme heat over Australia this autumn and the associated damage to the reef are also having an effect on the election campaign. As public concern over the future of the reef grows, the parties are being asked to defend their climate change policies.

Both major parties have made election commitments to the reef, with the Coalition announcing an extra A$6 million to tackle crown-of-thorns starfish (adding to a further A$171 million committed under the 2016 budget), and Labor an extra A$377 million over five years (A$500 million in total). While both Labor and the Coalition aim to improve water quality in the reef through their policies, the coral bleaching and death this year is linked with warm seas.

Whether we’ll be able to save parts of the reef largely depends on whether we reduce our greenhouse gas emissions and manage to prevent the rising trend in temperatures from continuing.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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

El Niño – what it will bring this year and how it could change with global warming

Catherine Gautier, University of California, Santa Barbara

As the summer ends, heat is dominating the meteorological landscape, with the warmest month ever recorded and the drought continuing unabated in California. At the same time, it is clear that an El Niño is building that is expected to culminate in the fall and last until the winter, with the possibility of it becoming a “mega” El Niño.

The hope in California is that the large amounts of precipitation usually associated with extreme El Niño events would lessen the impacts of the state’s multi-year drought by partly refilling reservoirs and groundwater, even as scientists caution that this might not happen to the degree needed to alter the present situation.

What drives the El Niño weather pattern and what do scientists know about El Niño under man-made greenhouse warming?

A tropical Pacific phenomenon with global influence

To be clear, El Niño is a tropical Pacific phenomenon, even though it represents the strongest year-to-year meteorological fluctuation on the planet and disrupts the circulation of the global atmosphere. When sea surface temperature changes – or anomalies – in the eastern equatorial Pacific exceed a certain threshold, it becomes an El Niño.

What are the mechanisms behind El Niño? In normal conditions in the tropical Pacific, the trade winds blow from east to west, driving ocean currents westwards underneath. These currents transport warm water that is heated by low-latitude solar radiation and eventually piles up in the western Pacific. As a result, heat accumulates in the upper ocean.

Under normal conditions, winds help carry warm water from east to west.
Michael McPhaden/NOAA

The warm water evaporates from the ocean surface, and the light, warm and humid air rises, leading to deep convection in the form of towering cumulonimbus clouds and heavy precipitation. As this air ascends, it reaches upper levels of the troposphere and returns eastwards to eventually sink over the cooler water of the eastern Pacific. This east-west (zonal) circulation is called the Walker Circulation.

What happens to the atmosphere and the ocean during El Niño?

This circulation gets disrupted every few years by El Niño or enhanced by La Niña, the opposite effect. This periodic, naturally occurring phenomenon is called the El-Niño Southern Oscillation (ENSO).

During the typical El Niño, the warm phase of that oscillation, the trade winds weaken, and episodic westerly wind bursts in the western equatorial Pacific generate internal waves into the ocean. These waves trigger the transport of the warm water from the west to the east of the basin.

During an El Niño, the trade winds weaken and change ocean circulation patterns.
Michael McPhaden/NOAA

This induces a reduction of the upwelling (upward motion) of cold water in the east, at the equator and along the coast. It also creates warm sea surface temperature anomalies along the equator from the international dateline in the Pacific to the coast of South America.

As the central part of the Pacific warms up during El Niño, the atmospheric convection that normally occurs over the western warm pool migrates to the central Pacific. That transfer of heat from the ocean to the atmosphere gives rise to extraordinary rainfall in the normally dry eastern equatorial Pacific. Warm air then flows from the west, feeding this convection and further weakening the east-west-flowing trade winds. This leads to further warming as this feedback loop amplifies the phenomenon and ensures that deep atmospheric convection and rainfall patterns are maintained in the central equatorial Pacific. El Niño eventually ends when changes in the ocean cause negative feedbacks that reverse the dynamics that create the El Niño effects.

How can El Niño affect weather in United States and rainfall in California?

In association with El Niño, the heat redistribution in the ocean creates a major reorganization of atmospheric convection, severely disrupting global weather patterns from Australia to India and from South Africa to Brazil.

El Niño years typically bring rain-carrying storms to the western US.
Stuart Rankin/flickr, CC BY-NC

What explains the specific effect on the US and California, however, is a particular type of connection – called extratropical teleconnections – between the heating generated by El Niño and North America. This heating excites wave trains, or groups of similar-sized atmospheric waves, that propagate northward, connecting the central equatorial Pacific to North America. This shifts the subtropical jet stream northward and induces a series of storms over California and the southern US, in general. The increased precipitation that ensues seems to only occur during a strong El Niño.

While El Niños have a rather “typical” signature in the tropics, their impacts over North America vary because other influences act in temperate climates. Nevertheless, most El Niño winters are mild over western Canada and parts of the northern central United States, and wet with anomalous precipitation over the southern United States from Texas to Florida.

How might El Niño evolve under man-made greenhouse warming?

Scientists are now studying the diversity in El Niño behavior – strong and weak ones, changes in duration, and the different regions for the maximum SST anomalies. Are these changes to El Niño related to global warming? It is too early to say.

For one thing, there is significant natural variability in the Pacific over the decade-length and longer time scales, which could be masking changes driven by global warming.

Climate models do suggest that the mean conditions in the Pacific will evolve toward a warmer state. That means sea surface temperatures are likely to rise and the trade wind to weaken, which could lead to a more permanent El Niño state and/or more intense El Niño events.

Some climate model projections, together with reconstructions of past El Niños, provide empirical support for more extreme El Niño events under greenhouse warming. They also point toward an eastward shift of the center point where heat from the ocean transfers to the air. This would mean an eastward shift of extratropical rainfall teleconnections, the phenomenon responsible for weather changes in North America, including more rain in the West.

But models diverge in their predictions of whether and how the teleconnections’ intensity will change. So there is no simple answer to how precipitation will change in California in association with changes of El Niño related to greenhouse warming.

A complex phenomenon with many tricks for scientists

Will the sensitivity of the atmosphere to the primary mechanism at the heart of El Niño – that is, feedback between the higher sea temperatures and slowing trade winds, leading to atmospheric convection over the central Pacific – continue in the future?

It was not maintained during 2014, when otherwise favorable conditions for a big El Niño were present. In that case, persistent deep convection did not occur in the central Pacific, and the usual strong interaction between the atmosphere and the ocean there failed to play its normal role in anchoring the convection and heat transfer.

These results show us that we still have much to learn. This is true despite the dramatic scientific progress that has been accomplished over the last few decades regarding El Niño and ENSO cycles, including new theories, sophisticated seasonal forecasting models and extensive observation systems.

Our ability to predict El Niño and the potential connections between increasing greenhouse gases and El Niño is still limited by the complexity of the ENSO dynamics, as exemplified by the failed prediction of a 2014 El Niño. In the meantime, we can look forward to a winter when El Niño, perhaps even a mega El Niño, will dominate the weather discussion.

Catherine Gautier, Professor Emerita of Geography, University of California, Santa Barbara

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

El Nino

As drought looms again, Australians are ready to embrace recycled water

Stuart Khan, UNSW Australia

Concerns about drought and water supply are once more building in eastern Australia. Recent reports from Victoria show the state government is considering switching on the so-far-unused desalination plant to supply Melbourne. While Melbourne doesn’t currently need extra water, this might free up other water allocated to the city to be diverted to regional communities in the north of the state where water shortages are looming.

When drought strikes, people and governments look to shore up water supplies. In Australia, politicians have focused on building more dams and long pipelines, at the expense of alternative sources such as recycled water.

It has been widely assumed that drinking recycled water, from sources such as sewage, is not acceptable to the public. But an Australia-first survey released by the Australian Water Association shows the public is ready to accept recycled water.

Water is getting further away and more expensive

Since colonisation, we have tapped increasingly distant, more energy-intensive and more expensive sources of fresh water.

We have constructed large dams to buffer variable water supplies through wet and dry seasons, as well as wet and dry years. As water consumption has exceeded the capacity of river basins to meet demand, we have constructed long pipelines, to pump water in from less populated river basins to more populated basins.

During the last decade, many of our major cities began to identify that the capacity to pump more water from distant locations was approaching sustainable limits.

New sources of water were required. So, in a very short period of time, cities including Perth, Sydney, Melbourne, Adelaide and the Gold Coast set about constructing seawater desalination plants.

Hindsight comes with 20-20 vision and it’s clear that most of these desalination decisions – with the notable exception of Perth’s – were premature since the plants have barely beeen used. Politicians and those with a financial interest in these plants often comment that the desal plants represent great “insurance policies” for when the next drought inevitably arrives.

However, these “insurance policies” came with billion-dollar price tags. Much of this has been externally financed, thus accruing significant annual interest costs.

Furthermore, the costs associated with maintaining desal plants are significant – even when they supply zero or negligible water. In some cases, such as Sydney, the real need to use the desal plant – given effective demand management – is likely to be still many years away. As such, it is arguable that these desal plants were very poor value insurance policies.

The lure of desalination

In 2006, the New South Wales Parliament undertook an Inquiry into a Sustainable Water Supply for Sydney. I appeared as a witness to that inquiry to put forward an argument that there was a more sustainable option than seawater desalination.

I argued that the technology was established to reliably purify water from sewage treatment plants to such a high degree that it would be capable of providing extremely high-quality drinking water for Sydney. This practice has been adopted in a number of US cities and is commonly referred to as “potable water recycling”.

All towns and cities are physically unique in terms of geography and historic development features. However, in the right mix of circumstances, potable water recycling can have significant advantages over seawater desalination.

These can include reduced operation and construction costs, as well as much lower energy requirements, which translate to reduced carbon emissions. Nonetheless, the suggestion that the NSW government seriously consider potable water recycling as an alternative to seawater desalination was not widely appreciated.

The general wisdom of the time was that Australians would not be prepared to accept water that was once sewage as a component of their drinking water supply. Indeed, this appeared to be supported by a telephone survey around that time.

Since then, the New South Wales and Victorian state governments have made statements that potable water recycling is not even an option for consideration by cities in those states.

Political thirst for dams

It is widely recognised that most opportunities for building dams on rivers to provide water for Australia’s large cities have been effectively exhausted.

Nonetheless, Australian politicians appear to yearn for opportunities to announce a new big dam project. When the federal member for Calare, John Cobb, announced a plan to dam the Belubula River at Needles Gap (NSW) in 2014, he declared: “I believe this project will lift the spirits of the central west and will inspire all of regional Australia.”

Water supply projects may have many diverse objectives, and inspiring all of regional Australia may be an understandably important one for a politician. However, many politicians appear to carry some unshakeable assumptions about community water supply preferences in Australia. Most seem to think we all want to hear announcements for new big dams.

And if we can’t have new big dams, they think desalination plants are our next preferred option. Few politicians deny the sustainability advantages of potable water recycling, but most seem to think it’s just too difficult to bring the community on board to support it.

Attitudes are changing

In the recent survey, 3,316 completed responses were received from community members across Australia.

Of these, 69% agreed or strongly agreed with the statement that recycled water “can be treated and managed for safe drinking”. This compared with 56% who agreed with the same statement for stormwater and 82% who agreed for seawater desalination.

Given the prevalence of actual seawater desalination plants around Australia and a lack of any public discussion about potable water recycling, I suggest that this level of faith in the capabilities of recycling plants is remarkable.

Recent research from the United States has shown that by engaging the community and providing accurate information, the underlying level of support for recycling can be significantly increased.

When consumers were asked whether they agree with the statement that “there is scope for more dams to provide additional water supplies in the south of Australia (e.g. in the Murray-Darling Basin and the south-east coastal areas)”, only 33% agreed. This rose to 46% for northern Australia. So much for inspiring all of regional Australia.

Preparing for the dry

Worldwide, countries are preparing for the significant El Niño event underway. Evidence is rapidly building that the east coast of Australia will again be subjected to the drought-causing conditions that have led to major water shortages in previous decades.

When this happens, we can expect many regional areas to struggle in their management of dwindling water supplies. Many will be searching for sustainable water supply solutions and some will identify potable water recycling as the most sustainable option for their circumstances.

The challenge for the federal and state governments will be to support the needs of these towns and cities. They will do that best by ensuring that all potential water supply options are on the table and given fair consideration.

In the meantime, our politicians would serve regional Australia best by ceasing to stigmatise potable water recycling as an option that is not even entitled to consideration.

Instead, they should work to build upon the support that currently exists in our communities so that when the need arises, potable water recycling is a viable and broadly accepted water supply solution. There is already powerful evidence that this can be achieved, when state governments work constructively toward this goal.

In 2013, the Western Australian government gave strong support and approval for a potable water recycling project to provide up to 20% of Perth’s water supply. That plant has since been constructed and will soon begin replenishing one of the city’s essential, but dwindling, groundwater supplies.

Stuart Khan, Associate Professor in Environmental Engineering, UNSW Australia

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