A wet winter, a soggy spring: what is the negative Indian Ocean Dipole, and why is it so important?


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Nicky Wright, University of Sydney; Andréa S. Taschetto, UNSW, and Andrew King, The University of MelbourneThis month we’ve seen some crazy, devastating weather. Perth recorded its wettest July in decades, with 18 straight days of relentless rain. Overseas, parts of Europe and China have endured extensive flooding, with hundreds of lives lost and hundreds of thousands of people evacuated.

And last week, Australia’s Bureau of Meteorology officially declared there is a negative Indian Ocean Dipole — the first negative event in five years — known for bringing wet weather.

But what even is the Indian Ocean Dipole, and does it matter? Is it to blame for these events?

What is the Indian Ocean Dipole?

The Indian Ocean Dipole, or IOD, is a natural climate phenomenon that influences rainfall patterns around the Indian Ocean, including Australia. It’s brought about by the interactions between the currents along the sea surface and atmospheric circulation.

It can be thought of as the Indian Ocean’s cousin of the better known El Niño and La Niña in the Pacific. Essentially, for most of Australia, El Niño brings dry weather, while La Niña brings wet weather. The IOD has the same impact through its positive and negative phases, respectively.

Positive IODs are associated with an increased chance for dry weather in southern and southeast Australia. The devastating Black Summer bushfires in 2019–20 were linked to an extreme positive IOD, as well as human-caused climate change which exacerbated these conditions.

Negative IODs tend to be less frequent and not as strong as positive IOD events, but can still bring severe climate conditions, such as heavy rainfall and flooding, to parts of Australia.

The Indian Ocean Dipole (IOD) index, used to track the variability of the Indian Ocean Dipole. An event occurs after the index crosses the threshold for 8 weeks.
Bureau of Meteorology

The IOD is determined by the differences in sea surface temperature on either side of the Indian Ocean.

During a negative phase, waters in the eastern Indian Ocean (near Indonesia) are warmer than normal, and the western Indian Ocean (near Africa) are cooler than normal.




Read more:
Explainer: El Niño and La Niña


This causes more moisture-filled air to flow towards Australia, favouring wind pattern changes in a way that promotes more rainfall to southern parts of Australia. This includes parts of Western Australia, South Australia, Victoria, NSW and the ACT.

Generally, IOD events start in late autumn or winter, and can last until the end of spring — abruptly ending with the onset of the northern Australian monsoon.

The negative phase of the Indian Ocean Dipole.
Bureau of Meteorology

Why should we care?

We probably have a wet few months ahead of us.

The negative IOD means the southern regions of Australia are likely to have a wet winter and spring. Indeed, the seasonal outlook indicates above average rainfall for much of the country in the next three months.

In southern Australia, a negative IOD also means we’re more likely to get cooler daytime temperatures and warmer nights. But just because we’re more likely to have a wetter few months doesn’t mean we necessarily will — every negative IOD event is different.

Rainfall outlooks for August–October suggest that large parts of Australia will likely experience above-median rainfall.
Bureau of Meteorology, CC BY

While the prospect of even more rain might dampen some spirits, there are reasons to be happy about this.

First of all, winter rainfall is typically good for farmers growing crops such as grain, and previous negative IOD years have come with record-breaking crop production.

In fact, negative IOD events are so important for Australia that their absence for prolonged periods has been blamed for historical multi-year droughts in the past century over southeast Australia.

Negative IOD years can also bring better snow seasons for Australians. However, the warming trend from human-caused climate change means this signal isn’t as clear as it was in the past.

A negative IOD may mean a better snow season in the High Country.
Shutterstock

It’s not all good news

This is the first official negative IOD event since 2016, a year that saw one of the strongest negative IOD events on record. It resulted in Australia’s second wettest winter on record and flooding in parts of NSW, Victoria, and South Australia.

The 2016 event was also linked to devastating drought in East Africa on the other side of the Indian Ocean, and heavy rainfall in Indonesia.

Thankfully, current forecasts indicate the negative IOD will be a little milder this time, so we hopefully won’t see any devastating events.

The number of Indian Ocean Dipole events (per 30 years) based on climate models.
Modified from Abram et al. (2020)

Is the negative IOD behind the recent wet weather?

It’s too early to tell, but most likely not.

While Perth is experiencing one of its wettest Julys on record, the southwest WA region has historically been weakly influenced by negative IODs.

Negative IODs tend to be associated with moist air flow and lower atmospheric pressure further north and east than Perth, such as Geraldton to Port Hedland.

Outside of Australia, there has been extensive flooding in China and across Germany, Belgium, and The Netherlands.

It’s still early days and more research is needed, but these events look like they might be linked to the Northern Hemisphere’s atmospheric jet stream, rather than the negative IOD.

The jet stream is like a narrow river of strong winds high up in the atmosphere, formed when cool and hot air meet. Changes in this jet stream can lead to extreme weather.

What about climate change?

The IOD — as well as El Niño and La Niña — are natural climate phenomena, and have been occurring for thousands of years, before humans started burning fossil fuels. But that doesn’t mean climate change today isn’t having an effect on the IOD.




Read more:
Why drought-busting rain depends on the tropical oceans


Scientific research is showing positive IODs — linked to drier conditions in eastern Australia — have become more common. And this is linked to human-caused climate change influencing ocean temperatures.

Climate models also suggest we may experience more positive IOD events in future, including increased chances of bushfires and drought in Australia, and fewer negative IOD events. This may mean we experience more droughts and less “drought-breaking” rains, but the jury’s still out.

When it comes to the recent, devastating floods overseas, scientists are still assessing how much of a role climate change played.

But in any case, we do know one thing for sure: rising global temperatures from climate change will cause more frequent and severe extreme events, including the short-duration heavy rainfalls associated with flooding, and heatwaves.

To avoid worse disasters in our future, we need to cut emissions drastically and urgently.




Read more:
You may have heard the ‘moon wobble’ will intensify coastal floods. Well, here’s what that means for Australia


The Conversation


Nicky Wright, Research Fellow, University of Sydney; Andréa S. Taschetto, Associate Professor, UNSW, and Andrew King, ARC DECRA fellow, The University of Melbourne

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

If you’re planning to hike this winter, invest in the right gear. Being unprepared for Australia’s harsh terrain can be deadly


Vanessa Adams, University of Tasmania; Jason Byrne, University of Tasmania, and Noelle Nemeth, University of TasmaniaTwo years ago, emergency workers rescued a hiker in Cradle Mountain-Lake St Clair National Park. He had spent nine days in his tent in freezing weather with dangerous blizzards, trying to keep dry from infiltrating snow and rain.

Because he was an experienced and prepared hiker, he had the skills and gear needed to keep himself safe and relatively warm until rescuers could find him. His preparedness ultimately led to his survival.

Such experiences, however, don’t always have happy endings.

Of the hikers, trekkers and bushwalkers who need rescuing from Australia’s harsh wilderness each year, a small proportion never make it back alive. And as we head into winter, the likelihood of accidents increases, especially in places like Tasmania.

Our recent research on hikers in Tasmania shows just how important preparedness is to prevent injuries and deaths. So let’s look at what it means to be prepared for a hike and who’s most at risk.

Slips, drops, hypothermia

Tasmania is quickly becoming known worldwide as a hiking destination, with Cradle Mountain National Park the crown jewel, from short two-hour walks to the multi-day Overland track.

In 2017-18, an estimated 280,000 people visited Cradle Mountain, and 9,000 hikers completed the Overland track between October and May.

Two hikers on a grassland trail
The Tassie wilderness provides awe-inspiring but physically demanding hikes for visitors.
Noelle Nemeth, Author provided

But in winter, Tasmania’s weather conditions can change rapidly, particularly in alpine areas that draw people in with the promise of snow-capped mountains. One hour it can be clear and sunny. The next, bad weather can worsen into a blizzard.

The island’s sometimes severe weather means risks are amplified. These can include getting lost, running out of food or water while sheltering, and having an accident such as falling from steep and slippery terrain.




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Across Tasmania, bushwalker rescues fluctuate substantially by year, from lows of six (2018) to highs of 44 (2019).

Of the recent hiker deaths in Tasmania, some have been due to falls from great heights, while others are attributed to a lack of preparation and appropriate gear causing hypothermia.

Hypothermia is life threatening. This video explains how you can be prepared in Tasmania’s parks and reserves.

For park management agencies, rescuing injured hikers or recovering the deceased can be dangerous and expensive. Estimated rescue costs range from a few hundred dollars to tens of thousands of dollars per incident.

At times, bad weather conditions means rescue agencies can’t access sites. They have to make the challenging decision not to respond to rescue calls, to protect the lives of volunteers and rescue staff.

What is preparedness and why does it matter?

Preparedness is about providing yourself with the necessary resources to safely tackle unexpected issues that may arise.

How prepared you are can be the difference between severe injury or death, and survival. We define preparedness as the process of:

  • packing essential clothing and equipment
  • conducting pre-planning and familiarisation with a destination (what are the weather conditions, or trail conditions like?)
  • self-assessment of capabilities (what’s your fitness level, and what are your wilderness knowledge and skills like?)
  • notifying others about your travel intentions.
Hiking boots overlooking a lake in Cradle Mountain
Wearing the right shoes on your next hike can save your life.
Shutterstock

Some hikers are better prepared than others

Our research surveyed overnight hikers in Tasmania. And we found a lack of preparedness is related to people’s backgrounds (such as age and sex) and behavioural traits (such as risk taking).

Young men, for example, appear more likely to take risks, overestimating their skills and experience. Some tourist groups, who are unfamiliar with local weather conditions and landscapes, are also at higher risk.

In many accidents, inadequate clothing or footwear is a culprit, such as lack of woollen base layers, hats and gloves, and waterproof outer layers. This can result in hypothermia, frostbite, falls and other major problems.




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We were surprised by what many hikers didn’t carry, including maps, compasses, whistles, and first aid kits — essential items for all hikers. Some told us they didn’t own that equipment, others thought it was unnecessary.

People in a tour group were less likely to carry food, a first aid kit and safety items, believing their guide would carry it for them. But if group members become separated, the consequences can be fatal.

Hiker beside an orange tent
Maps, compasses, whistles and first aid kits are essential on every hike.
Shutterstock

Our research also suggests hikers out for day trips or shorter walks, appear to feel there’s less risk and seem less prepared than if they were doing a longer trip.

They’re unlikely to take an emergency position indicating radio beacon (EPIRB) or personal locator beacon (PLB), which can send a distress signal and alert rescuers to your location in places with no phone reception. They may also wear sport shoes instead of hiking boots, and some don’t carry essential items for winter walking, such as a waterproof jacket or tent.

Being prepared with the right gear and experience is important regardless of how long you plan on being out. The reality is weather conditions can change suddenly, even if you’re not out for very long.

So how can you be better prepared?

In response to past hiker deaths, coronial inquests have identified better education, improved visitor management and safety measures as possible solutions.

But we’ve also identified a simple, but likely effective solution that could supplement a continued lack of appropriate gear: the use of a “gear library”.

A gear library would be set up at visitor centres where you’re usually expected to start hikes and would allow people to hire speciality gear items, such as personal safety devices (EPIRB, PLB). These can usually cost more than $200, but would be substantially cheaper in a gear library, ensuring rescue workers are notified and can find you after an accident.




Read more:
Stick to the path, and stay alive in national parks this summer


It’s also important to keep a checklist to pack essential items. Some key items include:

  • adequate supply of food and water, including contingency items for unexpected additional days hiking because of bad weather
  • warm clothes, such as a waterproof jacket with hood and storm front, waterproof over-trousers, sturdy walking boots and warm clothing (a fleece or woollen jumper, thermal base layers, hat and gloves)
  • appropriate footwear, such as hiking boots
  • a tent for overnight hikes
  • a first aid kit
  • a torch.

There are plenty of resources for people seeking information about how best to prepare for their bushwalk, including national park visitor centres, Westpac Rescue Tas and the Parks and Wildlife Tasmania website. These websites provide essential bushwalking guides on what to pack and how to prepare for bushwalking.

Anyone can safely enjoy a good day out in the Tasmanian wilderness — it’s beautiful, but can also be deadly. You can never be too prepared.




Read more:
Good signage in national parks can save lives. Here’s how to do it right


The Conversation


Vanessa Adams, Senior Lecturer, Discipline of Geography and Spatial Sciences, University of Tasmania; Jason Byrne, Professor of Human Geography and Planning, University of Tasmania, and Noelle Nemeth, Master’s Research Student, University of Tasmania

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

More people die in winter than summer, but climate change may see this reverse


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Ivan Charles Hanigan, University of Sydney; Alistair Woodward, University of Auckland, and Keith DearClimate change not only poses enormous dangers to the planet, but also harms human health. In our study published today, we show some of the first evidence climate change has had observable impacts on Australians’ health between 1968 and 2018.

We found long-term heating is associated with changed seasonal balance of deaths in Australia, with relatively more deaths in summer months and relatively fewer deaths in winter months over recent decades.

Our findings can be explained by the gradual global warming associated with climate change. Over the 51 years of our study, annual average temperatures increased by more than 1°C in Australia. The last decade (2011 to 2020) was the hottest in the country’s recorded history.

If we continue on this trajectory, we’re likely to see many more climate-related deaths in the years to come.

What we did and found

Using the Australian Institute of Health and Welfare, the Australian Bureau of Statistics and other sources, we gathered mortality data for people aged 55 and over between 1968 and 2018. We then looked at deaths in summer compared to winter in each year.

We found that in 1968 there were approximately 73 deaths in summer for every 100 deaths in winter. By 2018, this had risen to roughly 83 deaths in summer for every 100 deaths in winter.

The same trend, albeit of varying strength, was evident in all states of Australia, among all age groups over 55, in females and males, and in the three broad causes of death we looked at (respiratory, heart and renal diseases).

Elderly woman coughing with blanket over her
Historically, winter death rates have tended to be higher than in summer. But this is changing as our planet warms.
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Hot and cold weather can have a variety of direct and indirect effects on our health. Winter death rates generally exceed those in summer months because infectious diseases, like influenza, tend to circulate more in winter. Meanwhile, heat stress can exacerbate chronic health conditions including heart disease and kidney disease, particularly for older adults.

But the gap between cold-related deaths and heat-related deaths appears to be narrowing. And when we compared deaths in the hottest summers with the coldest winters, we found particularly warm years increase the likelihood of seasonal mortality ratios approaching 1 to 1 (meaning equal deaths in summer and winter).

With summers expected to become hotter, we believe this is an early indication of the effects of climate change in the future.




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Our research is unique

Globally, our study is one of very few that directly shows the health impacts of climate change. Most other studies examine the effects of past weather or climate conditions on health and extrapolate these into the future based on projected climate change scenarios, with associated uncertainties. For example, demographic characteristics of the population are likely to change over time.

Climate change occurs slowly, so typically, we need at least 30–50 years of records to accurately show how climate change is affecting health. Suitable health information is seldom available for such periods due to a variety of challenges in collecting electronic health data (especially in low- and middle-income countries).

Further, long-term health trends can be influenced by numerous non-climate related factors, such as improvements in health care.

In our study, we used Australian mortality records that have been collected with remarkable consistency of detail and quality over the last half century. And by focusing on the ratio of summer to winter deaths within each year, we avoid possible confounding associated with, say, improvements to health care.




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However, we were unable to consider some issues such as the different climate trends in small areas within each state/territory, or the effects of changing temperatures on different occupation groups, such as construction workers.

Our data also don’t allow us to account for the possible effects of people’s adaptation to warmer temperatures in the future.

Dry, cracked riverbed
Summer deaths will almost certainly increase in the years to come.
Shutterstock

Looking ahead

The changing ratio of summer to winter deaths has previously been identified as a possible warning sign of the impact of climate change on human health.

In one study on the topic, the authors found Australia may initially experience a net reduction in temperature-related deaths. That is, increased deaths from heat during summer would be offset by fewer deaths in winter, as winters become more mild.

However, they predict this pattern would reverse by mid-century under the business-as-usual emissions scenario, with increases in heat-related deaths outweighing decreases in cold-related deaths over the long term.

Our findings support these worrying predictions. If warming trends continue, it’s almost certain summer deaths will increase, and come to dominate the burden of temperature-related deaths in Australia.

We found the speed of change in the ratio of summer to winter deaths was fastest in the hottest years within each decade. This strengthens our conclusion we’re observing an effect of long-term climate change.




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Besides helping to answer the question, “does climate change affect human health?”, we believe our findings should inform planning for climate change mitigation and adaptation. The implications are considerable for the planning of hospital services and provision of health care, as well as for emergency services, housing, energy supply, holiday periods and bushfire disaster preparedness.The Conversation

Ivan Charles Hanigan, Data Scientist (Epidemiology), University of Sydney; Alistair Woodward, Professor, School of Population Health, University of Auckland, and Keith Dear, Adjunct Professor of Public Health

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

Under climate change, winter will be the best time for bush burn-offs – and that could be bad news for public health


Giovanni Di Virgilio, UNSW; Annette Hirsch, UNSW; Hamish Clarke, University of Wollongong; Jason Evans, UNSW; Jason Sharples, UNSW, and Melissa Hart, UNSW

At the height of last summer’s fires, some commentators claimed “greenies” were preventing hazard reduction burns – also known as prescribed burns – in cooler months. They argued that such burns would have reduced the bushfire intensity.

Fire experts repeatedly dismissed these claims. As then NSW Rural Fire Service Commissioner Shane Fitzsimmons noted in January this year, the number of available days to carry out prescribed burns had reduced because climate change was altering the weather and causing longer fire seasons.




Read more:
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This public conversation led our research team to ask: if climate change continues at its current rate, how will this change the days suitable for prescribed burning?

Our results, published today, were unexpected. Climate change may actually increase the number of burn days in some places, but the windows of opportunity will shift towards winter months. The bad news is that burning during these months potentially increases the public health impacts of smoke.

A hot debate

Hazard reduction involves removing vegetation that could otherwise fuel a fire, including burning under controlled conditions. But its effectiveness to subdue or prevent fires is often debated in the scientific community.

Commissioner Fitzsimmons weighs in on a national debate about hazard-reduction burns.

Those with experience on fire grounds, including Fitzsimmons, say it’s an important factor in fire management, but “not a pancea”.

Despite the debate, it’s clear hazard reduction burning will continue to be an important part of bushfire risk management in coming decades.




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Modelling future weather

Before conducting prescribed burns, firefighting agencies consider factors such as vegetation type, proximity to property, desired rate of spread and possible smoke dispersal over populated areas. But we wanted to distil our investigation down to daily weather factors.

We reduced those factors to five key components. These were maximum temperature, relative humidity, wind speed, fuel moisture and the McArthur forest fire danger index (the index used to forecast fire danger in southeast Australia).

We looked at these elements on prescribed burning days between 2004-2015. We then used climate models to simulate how the conditions would change with global warming over southeast Australia, relative to a baseline historical 20-year period for 1990-2009.

To make a valid 20-year comparison, we compared the historical period to a modelled period from 2060-2079, assuming emissions continue to rise at their current pace.

A controlled burn in bushland, with small flames and lots of smoke.
Under global warming, suitable conditions for prescribed burns will be shifted to late winter and early spring in many places.
Shutterstock

Surprisingly, we found, with one regional exception, the number of days suitable for prescribed burning did not change. And in many places, the number increased.

As the fire season lengthened under a warming climate, the number of days suitable for burning just shifted from autumn to winter.

Shifting seasons

Our research indicated that by 2060 there’ll be fewer prescribed burning days during March, April and May. These are the months when most burning happens now.

But there will be significantly more opportunities for burning days from June to October. This is because the conditions that make for a good day for prescribed burning – such as mild and still days – start to shift to winter. Today, weather in these months is unsuitable for conducting burns.

Interestingly, these results aren’t uniform across southeast Australia. For example, much of the Australian east coast and South Australia would see seasonal shifts in burning windows, with around 50% fewer burning days in March to May.

Much of Victoria and in particular the southern regions saw an increase in burning windows during April to May and, in some parts of the state, through September and October as well.

Only the east Queensland coast would see a total reduction in prescribed burn days from April to October.

The smoke trap

This may be good news for firefighters and those agencies who depend on prescribed burning as a key tool in bushfire prevention. But, as so often is the case with climate change, it’s not that simple.

A byproduct of prescribed burning is smoke, and it’s a very significant health issue.

Last year, research showed global warming will strengthen an atmospheric layer that traps pollution close to the land surface, known as the “inversion layer”. This will happen in the years 2060-79, relative to 1990-2009 – especially during winter.




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Unfortunately, the conditions that create inversion layers – including cool, still air – correspond with conditions suitable for prescribed burning.

For asthmatics and those sensitive to air pollution, smokier burn days could make winter months more difficult and add further stress to the health system.

It also creates an additional challenge for firefighting agencies, which must already consider whether smoke will linger close to the surface and potentially drift into populated regions during prescribed burns.

This is just one factor our firefighting agencies will need to face in the future as bushfire risk management becomes more complex and challenging under climate change.




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How does bushfire smoke affect our health? 6 things you need to know


The Conversation


Giovanni Di Virgilio, Research associate, UNSW; Annette Hirsch, Post Doctoral Research Fellow, UNSW; Hamish Clarke, Research Fellow, University of Wollongong; Jason Evans, Professor, UNSW; Jason Sharples, Professor of Bushfire Dynamics, School of Science, UNSW Canberra, UNSW, and Melissa Hart, Graduate Director, ARC Centre of Excellence for Climate Extremes, UNSW

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

Winter storms are speeding up the loss of Arctic sea ice



A scientist checks cracks in the Arctic sea ice after a storm (April 2015, N-ICE2015 expedition).
Amelie Meyer/NPI, Author provided

Amelie Meyer, University of Tasmania

Arctic sea ice is already disappearing rapidly but our research shows winter storms are now further accelerating sea ice loss.




Read more:
Arctic breakdown: what climate change in the far north means for the rest of us


The research is based on data we gathered during an expedition on a small Norwegian research vessel, the Lance, that was left to drift in the Arctic sea ice for five months in 2015.

Time series of air temperature anomalies in the Arctic for the period 1981-2010: Temperatures in the Arctic in May and June 2019 period were the warmest in the satellite records.
Zack Labe (@ZLabe)

The expedition was intense and felt more like going to the Moon than going on a typical research cruise. What took us by surprise were the many winter storms that battered the ice (and our ship and ice camp).

It has taken us years to collate these data but now we know the winter storms play a key role in the fate of Arctic sea ice, particularly in the Atlantic sector of the Arctic.

Norwegian research vessel ‘Lance’ frozen in the Arctic sea ice in February 2015 during the N-ICE2015 expedition.
Paul Dodd (NPI)

How winter storms amplify climate change

On average, about 10 extreme storms will reach all the way to the North Pole each winter. While these winter storms are short (they last on average 6-48 hours), they can be incredibly intense.

During a storm in winter 2015 we saw the air temperature rise from -40℃ (-40℉) to 0℃ (32℉) in just a day, and then fall back to -30℃ (-22℉) the next day, when cold Arctic air returned after the storm.

These storms bring heat, moisture and strong winds into the Arctic, and next we look at how they impact sea ice and its surroundings.

Warming and weakening the ice

The heat from the storms warms up the air, snow and ice, slowing down the growth of the ice. Moisture from the storms falls as snow on the ice. After the storm, the blanket of snow insulates the ice from the cold air, further slowing the growth of the ice for the remainder of winter.

The strong winds during the storms push the ice around and break it into pieces, making it more fragile and deforming it, more like a boulder field.

The strong winds also stir the ocean below the ice, mixing up warmer water from deeper waters to the surface where it melts the ice from below. This melting of the ice in the middle of winter can happen for several days after the storms when the air is already back to well below freezing.

Processes related to Arctic winter storms. In the first storm phase, strong southerly winds compress the ice cover and transport warm air, moisture, and bring strong winds. In the second phase, northerly winds transport ice southwards. After the storm has passed, cold and calm conditions return, allowing new ice to grow in leads. When the next winter storm arrives, it further drives the ice cover into a relatively thin-ice, snow-covered mosaic of strongly deformed ice floes. These new conditions impact surrounding ecosystems by shaping habitats and light conditions.
Graham et al., 2019 (Scientific Reports)

Thinner ice, shelter for life and accelerated melting

The breakup of the ice opens big passages of open water between ice floes, called leads. In winter these passages end up refreezing rapidly, generating new super-thin ice.

These thinner refrozen patches of ice let more light through in the following spring, allowing ocean plants (phytoplankton) to bloom earlier.

The rougher sea ice landscape becomes a shelter for many ice-associated Arctic organisms, including ice algae, becoming biological hot spots in the following spring.

The broken up and deformed ice drifts faster, reaching warmer waters where it melts sooner and faster.

So really, winter storms precondition the ice to a faster melt in the following spring with an impact that continues well into the following season.

Why is Arctic sea ice declining?

Winter sea ice cover in the Atlantic sector of the Arctic has been retreating at a record breaking pace, especially in the Barents Sea off Norway and Russia.

Average September Arctic sea ice extent from 1979 to 2018. Black line shows monthly average for each year; blue line shows the trend.
National Snow and Ice Data Center

The Arctic is particularly sensitive to human driven climate change. We know the decrease in sea ice is due to both the warming of the Arctic (air and ocean) and changing wind patterns that break up the ice cover.

But there are also amplifying mechanisms or “feedback” mechanisms, in which one natural process reinforces another. Their role in the decrease of sea ice is hard to predict. We now know winter storms in the Arctic contribute to these feedback mechanisms.

More storms ahead

Arctic winter storms are increasing in frequency and this is likely due to climate change.

With the thinner Arctic sea ice cover and shallower warmer water in the Arctic Ocean, the mechanisms we observed during the winter storms will likely strengthen and the overall impact of winter storms on Arctic ice is likely to increase in the future.

Two weeks ago, the Arctic sea ice reached its minimum extent for 2019, after another winter of intense winter storms. The minimum ice extent was effectively tied for second lowest since modern record-keeping began in the late 1970s, along with 2007 and 2016, reinforcing the long-term downward trend in Arctic ice extent. Arctic sea ice has been declining for at least 40 years, and amplifying mechanisms such as the winter storms are accelerating this retreat.

Arctic sea ice extent just reached its annual minimum extent for 2019 on September 18. This season was a tie for the 2nd lowest on record, along with 2007 and 2016 and behind 2012, which holds the overall record minimum.
Zack Labe (@ZLabe)

As highlighted in the recent IPCC Ocean and Cryopshere report, these changes in September sea ice are likely unprecedented for at least 1,000 years.

Remember also that changes in the Arctic don’t just affect the immediate region: Arctic warming has been linked to the polar vortex, and weather extremes across central Europe and north America.




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As we start taking into account feedback mechanisms like the winter storms, our predictions for the first Arctic sea ice free summer are indicating it will likely happen before 2050.The Conversation

Amelie Meyer, Research fellow, University of Tasmania

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

The winter was dry, the spring will likely be dry – here’s why


Jonathan Pollock, Australian Bureau of Meteorology and Andrew B. Watkins, Australian Bureau of Meteorology

Winter still has a few days to run, but it’s highly likely to be one of Australia’s warmest and driest on record. While final numbers will be crunched once August ends, this winter will probably rank among the top ten warmest for daytime temperatures and the top ten driest for rainfall.

While it was drier than average across most of the country, it was especially dry across South Australia, New South Wales and southern Queensland. Small areas of South Australia and New South Wales are on track for their driest winter on record.




Read more:
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In contrast, parts of southern Victoria, western Tasmania and central Queensland were wetter than usual.

Preliminary winter 2019 rainfall deciles.
Bureau of Meteorology

Thirsty ground

Soil moisture normally increases during winter (except in the tropics, where it’s the dry season), and while we saw that in parts of Victoria, for most of Queensland and New South Wales the soil moisture actually decreased.

Dry soils leading into winter have soaked up the rain that has fallen, resulting in limited runoff and inflows into the major water storages across the country.

A glass half empty

Sydney’s water storages dropping below 50% received considerable public attention, and unfortunately a number of other regional storages in New South Wales and the Murray Darling Basin are much lower than that.

The winter ‘filling’ season in the southern Murray Darling Basin has been drier than usual for the third year in a row, and storages in the northern Murray Darling basin are extremely low or empty with no meaningful inflows.

Some rain in the west

Some regions did receive enough rainfall to grow crops this cool season. However, northern New South Wales and southern Queensland didn’t see an improvement in their severe year-to-date rainfall deficiencies over winter.

In fact, the area of the country that is experiencing year-to-date rainfall in the lowest 5% of historical records expanded.

In better news, the severe year-to-date deficiencies across southwest Western Australia shrank during winter.

Indian Ocean Dipole the culprit

Sustained differences between sea surface temperatures in the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole (IOD). The IOD impacts Australian seasonal rainfall and temperature patterns, much like the more well known El Niño–Southern Oscillation.

Warm sea surface temperatures in the tropical western Indian Ocean and cool sea surface temperatures in the eastern Indian Ocean, along with changes in both cloud and wind patterns, have been consistent with a positive Indian Ocean Dipole since late May.

International climate models, some of which forecast the positive IOD as early as February, agree that it is likely to continue through spring.

Typically, this means below average rainfall and above average temperatures for much of central and southern Australia, which is consistent with the current rainfall and temperature outlook from the Bureau’s dynamical computer model. The positive IOD is likely to be the dominant climate driver for Australia during the next three months.

Comparison of international climate model forecasts of the IOD index for November 2019.
Models from the Australian Bureau of Meteorology, Canadian Meteorological Centre, European Centre for Medium-Range Weather Forecasts, Meteo France, National Aeronautics and Space Administration (USA) and the Met Office (UK)

A dry end to 2019 likely

Chances are the remainder of 2019 will be drier than normal for most of Australia. The exceptions are western Tasmania, southern Victoria and western WA, where chances of a wetter or drier than average end to the year are roughly equal.

The spring 2019 outlook showing low chances of above average rainfall for most of the country.
Bureau of Meteorology

Warmer than average days are very likely (chances above 80%) for most of the country except the far south of the mainland, and Tasmania.

Nights too are likely to be warmer than average for most of the country. However, much of Victoria and Tasmania, and southern parts of South Australia and New South Wales have close to an even chance for warmer than average minimum temperatures.

Due to the warm and dry start to the year, the east coast of Queensland, New South Wales, Victoria and Tasmania, as well as parts of southern Western Australia, face above normal fire potential this coming bushfire season.

More outlooks more often

The term weather describes conditions over shorter periods, such as from minutes to days, while the term climate describes the more slowly varying aspects of the atmosphere.

From today, the Bureau of Meteorology is closing the forecast gap between weather and climate information with the release of weekly and fortnightly climate outlooks.

For the first time, rainfall and temperature outlooks for the weeks directly after the 7-day forecast are available. One- and two-week outlooks have been added to complement the existing 1-month and 3-month outlooks.




Read more:
Why Sydney residents use 30% more water per day than Melburnians


The new outlook information for the weeks ahead also features how much above or below average temperatures are likely to be, and the likelihood of different rainfall totals.

The Bureau’s outlook videos explain the long-range forecast for the coming months.
Bureau of Meteorology


You can find climate outlooks and summaries on the Bureau of Meteorology website here.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology and Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology

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