How climate change can make catastrophic weather systems linger for longer


Steve Turton, CQUniversity Australia

Many parts of Australia have suffered a run of severe and, in some cases, unprecedented weather events this summer. One common feature of many of these events – including the Tasmanian heatwave and the devastating Townsville floods – was that they were caused by weather systems that parked themselves in one place for days or weeks on end.

It all began with a blocking high – so-called because it blocks the progress of other nearby weather systems – in the Tasman Sea throughout January and early February.

This system prevented rain-bearing cold fronts from moving across Tasmania, and led to prolonged hot dry northwesterly winds, below-average rainfall and scorching temperatures.




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Meanwhile, to the north, an intense monsoon low sat stationary over northwest Queensland for 10 days. It was fed on its northeastern flank by extremely saturated northwesterly winds from Indonesia, which converged over the greater northeast Queensland area with strong moist trade winds from the Coral Sea, forming a “convergence zone”.

Ironically, these trade winds originated from the northern flank of the blocking high in the Tasman, deluging Queensland while leaving the island state parched.

Unusually prolonged

Convergence zones along the monsoon trough are not uncommon during the wet season, from December to March. But it is extremely rare for a stationary convergence zone to persist for more than a week.

Could this pattern conceivably be linked to global climate change? Are we witnessing a slowing of our weather systems as well as more extreme weather?

There does seem to be a plausible link between human-induced warming, slowing of jet streams, blocking highs, and extreme weather around the world. The recent Tasman Sea blocking high can be added to that list, along with other blocking highs that caused unprecedented wildfires in California and an extreme heatwave in Europe last year.

There is also a trend for the slowing of the forward speed (as opposed to wind speed) of tropical cyclones around the world. One recent study showed the average forward speeds of tropical cyclones fell by 10% worldwide between 1949 and 2016. Meanwhile, over the same period, the forward speed of tropical cyclones dropped by 22% over land in the Australian region.

Climate change is expected to weaken the world’s circulatory winds due to greater warming in high latitudes compared with the tropics, causing a slowing of the speed at which tropical cyclones move forward.

Obviously, if tropical cyclones are moving more slowly, this can leave particular regions bearing the brunt of the rainfall. In 2017, Houston and surrounding parts of Texas received unprecedented rainfall associated with the “stalling” of Hurricane Harvey.

Townsville’s floods echoed this pattern. Near the centre of the deep monsoon low, highly saturated warm air was forced to rise due to colliding winds, delivering more than a year’s worth of rainfall to parts of northwest Queensland in just a week.

The widespread rain has caused significant rises in many of the rivers that feed into the Gulf of Carpentaria and the Great Barrier Reef lagoon, and some runoff has made it into the Channel Country and will eventually reach Lake Eyre in South Australia. Unfortunately, little runoff has found its way into the upper reaches of the Darling River system.

Satellite images before (right) and after (left) the floods in northwest Queensland.
Courtesy of Japan Meteorological Agency, Author provided

Huge impacts

The social, economic and environmental impacts of Australia’s recent slow-moving weather disasters have been huge. Catastrophic fires invaded ancient temperate rainforests in Tasmania, while Townsville’s unprecedented flooding has caused damage worth more than A$600 million and delivered a A$1 billion hit to cattle farmers in surrounding areas.

Townsville’s Ross River, which flows through suburbs downstream from the Ross River Dam, has reached a 1-in-500-year flood level. Some tributaries of the dam witnessed phenomenal amounts of runoff, reliably considered as a 1-in-2,000-year event

Up to half a million cattle are estimated to have died across the area, a consequence of their poor condition after years of drought, combined with prolonged exposure to water and wind during the rain event.




Read more:
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Farther afield, both Norfolk Island and Lord Howe Island – located under the clear skies associated with the blocking high – have recorded exceptionally low rainfall so far this year, worsening the drought conditions caused by a very dry 2018. These normally lush subtropical islands in the Tasman Sea are struggling to find enough water to supply their residents’ and tourists’ demands.

Many parts of Australia have tolerated widespread extreme weather events this year, including some records. This follows a warm and generally dry 2018. In fact, 9 of the 10 warmest years on record in Australia have occurred since 2005, with only 1998 remaining from last century with reliable records extending back to 1910. Steady warming of our atmosphere and oceans is directly linked to more extreme weather events in Australia and globally.

If those extreme weather events travel more slowly across the landscape, their effects on individual regions could be more devastating still.The Conversation

Steve Turton, Adjunct Professor of Environmental Geography, CQUniversity Australia

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

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Ice melt in Greenland and Antarctica predicted to bring more frequent extreme weather



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A new climate model combines data on ice loss from both polar regions for the first time.
Mark Brandon, CC BY-ND

Nick Golledge, Victoria University of Wellington

Last week, rivers froze over in Chicago when it got colder than at the North Pole. At the same time, temperatures hit 47℃ in Adelaide during the peak of a heatwave.

Such extreme and unpredictable weather is likely to get worse as ice sheets at both poles continue to melt.

Our research, published today, shows that the combined melting of the Greenland and Antarctic ice sheets is likely to affect the entire global climate system, triggering more variable weather and further melting. Our model predictions suggest that we will see more of the recent extreme weather, both hot and cold, with disruptive effects for agriculture, infrastructure, and human life itself.

We argue that global policy needs urgent review to prevent dangerous consequences.




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Accelerated loss of ice

Even though the goal of the Paris Agreement is to keep warming below 2℃ (compared to pre-industrial levels), current government pledges commit us to surface warming of 3-4℃ by 2100. This would cause more melting in the polar regions.

Already, the loss of ice from ice sheets in Antarctica and Greenland, as well as mountain glaciers, is accelerating as a consequence of continued warming of the air and the ocean. With the predicted level of warming, a significant amount of meltwater from polar ice would enter the earth’s oceans.

The West Antarctic Ice Sheet is considered more vulnerable to melting, but East Antarctica , once thought to be inert, is now showing increasing signs of change.
Nick Golledge, CC BY-ND

We have used satellite measurements of recent changes in ice mass and have combined data from both polar regions for the first time. We found that, within a few decades, increased Antarctic melting would form a lens of freshwater on the ocean surface, allowing rising warmer water to spread out and potentially trigger further melting from below.

In the North Atlantic, the influx of meltwater would lead to a significant weakening of deep ocean circulation and affect coastal currents such as the Gulf Stream, which carries warm water from the tropics into the North Atlantic. This would lead to warmer air temperatures in Central America, Eastern Canada and the high Arctic, but colder conditions over northwestern Europe on the other side of the Atlantic.

Recent research suggests that tipping points in parts of the West Antarctic Ice Sheet may have already been passed. This is because most of the ice sheet that covers West Antarctica rests on bedrock far below sea level – in some areas up to 2 kilometres below.




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


Bringing both poles into one model

It can be a challenge to simulate the whole climate system because computer models of climate are usually global, but models of ice sheets are typically restricted to just Antarctica or just Greenland. For this reason, the most recent Intergovernmental Panel of Climate Change (IPCC) assessment used climate models that excluded ice sheet interactions.

Global government policy has been guided by this assessment since 2013, but our new results show that the inclusion of ice sheet meltwater can significantly affect climate projections. This means we need to update the guidance we provide to policy makers. And because Greenland and Antarctica affect different aspects of the climate system, we need new modelling approaches that look at both ice sheets together.

When the edges of the West Antarctic Ice Sheet start to recede, they retreat into deeper and deeper water and the ice begins to float more easily.
Mark Brandon, CC BY-ND

Seas rise as ice melts on land

Apart from the impact of meltwater on ocean circulation, we have also calculated how ongoing melting of both polar ice caps will contribute to sea level. Melting ice sheets are already raising sea level, and the process has been accelerating in recent years.

Our research is in agreement with another study published today, in terms of the amount that Antarctica might contribute to sea level over the present century. This is good news for two reasons.

First, our predictions are lower than one US modelling group predicted in 2016. Instead of nearly a metre of sea level rise from Antarctica by 2100, we predict only 14-15cm.

Second, the agreement between the two studies and also with previous projections from the IPCC and other modelling groups suggests there is a growing consensus, which provides greater certainty for planners. But the regional pattern of sea level rise is uneven, and islands in the southwest Pacific will most likely experience nearly 1.5 times the amount of sea level rise that will affect New Zealand.

While some countries, including New Zealand, are making progress on developing laws and policies for a transition towards a low-carbon future, globally policy is lagging far behind the science.

The predictions we make in our studies underline the increasingly urgent need to reduce greenhouse gas emissions. It might be hard to see how our own individual actions can save polar ice caps from significant melting. But by making individual choices that are environmentally sustainable, we can persuade politicians and companies of the desire for urgent action to protect the world for future generations.The Conversation

Nick Golledge, Associate Professor of Glaciology, Victoria University of Wellington

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

When extreme weather wipes out wildlife, the fallout can last for years


Sean Maxwell, The University of Queensland and James Watson, The University of Queensland

The recent heatwaves have proved deadly to many Australian animals, from feral horses to flying foxes.

And it’s not just heatwaves that can cause mass die-offs. Last year, flooding rain wiped out entire Antarctic penguin colonies, while drought has previously caused mass mangrove diebacks around the Gulf of Carpentaria.

These events generate headlines, but what about the aftermath? And are these catastrophic events part of a wider pattern?




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Killer climate: tens of thousands of flying foxes dead in a day


Our research describes how species have responded to extreme weather events over the past 70 years. These responses can tell us a great deal about how species are likely to cope with change in the frequency and intensity of extreme events in coming years.

We reviewed 517 studies, dating back to 1941 and conducted throughout the world, that examined how birds, mammals, fish, amphibians, reptiles, invertebrates or plants have responded to droughts, cyclones, floods, heatwaves, and cold snaps.

We found more than 100 cases of dramatic population declines. In a quarter of these cases, population numbers showed no sign of recovery long after the event. And in most cases, extreme events reduced populations of common species that play an important role in maintaining ecosystem integrity.

For example, extreme drought in the 2000s drove massive population declines of invertebrate freshwater species across Australia’s Murray-Darling Basin, and populations of buffalo, waterbuck, and kudu along the Zambezi River in Zimbabwe suffered severe and persistent declines following droughts in the 1980s.

We also found 31 cases of populations completely disappearing after an extreme event. Large populations of lizards and spiders were eradicated after Hurricane Lilli struck the Bahamas in 1996, for example. These populations had begun to recover one year after Lilli, but in half of all the cases of local population extinction, the species was still absent years or decades after exposure to an extreme event.

Negative responses were the most commonly reported, and also included habitat loss, declines in species numbers, and declines in reproductive fitness after an extreme event. These impacts clearly pose a serious risk to the longevity of many species, and to threatened species in particular. Kosciuszko National Park, for example, is a stronghold for the endangered northern corroboree frog, but 42% of its breeding sites in the park were rendered unusable by severe drought conditions throughout the 2000s.

Is there an upside?

Alongside the many negative impacts, we also found a larger‐than‐expected number of positive or neutral responses to extreme events (21% of all responses). This is a reminder that natural disturbances from extreme events often play a crucial role in the natural dynamics of an ecosystem.

Unfortunately, however, in many cases it was invasive species that benefited from extreme events. Flooding in southern Minnesota in 2004, for example, led to the rapid incursion of invasive green sunfish into streams, and cyclones accelerated the invasion of sweet pittosporum in Jamaican rainforests in the 1990s.

Cases of extreme events benefiting threatened species were uncommon, but included rainforest frogs becoming less susceptible to a fungal pathogen, chytrid fungus, after cyclones reduced rainforest canopy cover.

We also identified a range of “ambiguous” responses, including changes in diet or foraging behaviour, and changes in the types of species inhabiting a study area. Changes in invertebrate communities were particularly prevalent (87 cases). In 18 of these cases, the changes were long-lasting. However, most of the studies we reviewed lasted less than one year, and did not monitor for long-term recovery following an extreme event. This limits our ability to assess the long-term implications of extreme events on the species composition of ecosystems.

Avoiding future impacts

The one failsafe option for helping species cope with extreme events is to retain intact habitats, as these are the places where species are most resilient to extreme events. Intact habitats are contiguous areas of water or native vegetation that often span various altitudes, temperatures and rainfall patterns. These places can also act as important refuges for species that rely on long breaks between extreme events to recover.

Where intact habitat protection is not possible, restoring land or seascapes can also help species to adapt to extreme events. For example, long-term restoration efforts (that is, those that will be effective for at least 15 years) in brackish marshes help plant and animal communities cope with drought events.

Ecological restoration that helps species to adapt to extreme events can also benefit humans too. For instance, coastal communities can use oyster reefs or seagrass beds to guard against flooding.




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Climate change has already increased the intensity and frequency of extreme events across the world, and the trend is expected to accelerate in the future. Recognising the importance of planning for extreme events is essential for helping species cope with climate change. Building resilience to extreme events may also provide an opportunity to reduce the vulnerability of humans too.

Governments, local councils, and local communities are under increasing pressure to plan for extreme climate events. We now need similar recognition of the importance of extreme events in threatened species planning efforts. Right now, this planning is virtually non-existent, and that needs to change.The Conversation

Sean Maxwell, Postdoctoral fellow, The University of Queensland and James Watson, Professor, The University of Queensland

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

Trust Me, I’m An Expert: Australia’s extreme weather



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Australia’s cyclone season lies ahead.
NASA / ESRSU / Seán Doran, CC BY-NC-SA

Madeleine De Gabriele, The Conversation and Wes Mountain, The Conversation

It’s easy to write off Australia’s extreme weather as business as usual. We deal with floods, droughts, cyclones and other wild events every year. But as climate change raises global temperatures, are the droughts happening more often? Are the floods getting worse?

The October episode of Trust Me, I’m An Expert looks back through colonial evidence and prehistoric records, and forward to the Bureau of Meteorology’s Cyclone Weather Outlook for the year ahead.

The full episode will be released on October 8, but today you can catch a little of our interview with the Bureau of Meteorology’s Andrew Watkins. Keep an eye out for the full episode, where we ask: are we in uncharted territory, or is this life as usual on a changeable continent?




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Trust Me I’m An Expert is a monthly podcast from The Conversation, where we bring you stories, ideas and insights from the world of academic research.

You can download previous episodes of Trust Me here. And please do check out other podcasts from The Conversation – including The Conversation US’ Heat and Light, about 1968 in the US, and The Anthill from The Conversation UK, as well as Media Files, a brand new podcast all about the media.

You can find all our podcasts over here.

Music:




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The Conversation


Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation and Wes Mountain, Deputy Multimedia Editor, The Conversation

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

Health Check: how can extreme heat lead to death?



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Our climate is going to get warmer, and we need to protect ourselves from heat-related illness.
from shutterstock.com

David Shearman, University of Adelaide

Our climate is becoming hotter. This is our reality. Extreme heat is already responsible for hundreds of deaths every year. It’s a big environmental killer, and deaths from heatwaves in Australian cities are expected to double in the next 40 years.

Those most at risk are the elderly, people with chronic illness, those living in socioeconomic disadvantage, outdoor workers, and athletes who play their sport in brutally high temperatures. But extreme heat can affect anyone at any age.

So, what happens in our body during times of extreme heat? And how can it lead to fatal consequences?




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How we lose and gain heat

Our core body temperature sits at around 37℃. If it rises or falls, a range of very efficient physiological mechanisms come into play. In good health, our body can usually cope well with deviations of about 3.5℃, but beyond that the body begins to show signs of distress.

In hot weather, the body maintains core temperature by losing heat in several ways. One is to transfer it to a cooler environment, such as surrounding air or water, through our skin. But if the surrounding temperature is the same or higher than the skin (greater than 35-37℃) the effectiveness of this mechanism is markedly reduced.

Blood vessels supplying blood to the skin dilate. This allows more warm blood to flow near the surface of the skin, where the heat can be lost to the air. That’s why some people’s skin looks redder in hot environments.

One way the body loses heat is by directly transferring it to a cooler environment.
from shutterstock.com

Evaporation (or sweat) is another way to lose heat from the body. If there is enough airflow and humidity is low enough, we can lose large amounts of heat through sweat. But on humid days, the rate of evaporation is reduced, as the air cannot absorb so much if it is already saturated with water vapour.

We can also reduce our heat production by resting. About 80% of the energy produced by working muscles is heat, so any activity will increase the amount of heat the body has to lose. This is why athletes and outdoor manual workers are at particular risk when performing at high levels of physical activity.




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What happens if the body can’t lose heat

Heat stress describes a spectrum of heat-related disorders that occur when the body fails to lose heat to maintain core temperature. Heat stress ranges from heat cramps to heat exhaustion (pale, sweating, dizzy and fainting). If the core temperature rises above 40.5℃, it can lead to heatstroke, which is a medical emergency, can occur suddenly and often kills.

The hypothalamus works as the body’s thermostat.
from shutterstock.com

Heatstroke is caused by a failure of the hypothalamus, the region of the brain that works as our thermostat and co-ordinates our physiological response to excessive heat. It’s what leads to mechanisms like sweating and rapid breathing, dilated veins and increased blood flow to the skin. So, when the hypothalamus fails, so does our ability to sweat and lose heat in other ways.

At temperatures higher than 41.5℃, convulsions are common. Irreversible brain damage can occur at temperatures above 42.5℃. Patients with heatstroke can show neurological signs such as lack of co-ordination, confusion, seizures and loss of consciousness.




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When sweating stops, the skin may become hot and dry, heart rate and breathing increase and blood pressure is low. Cells and nerves in the body become damaged. Liver damage is also common, but may not manifest for several days. The kidneys stop working, normal blood clotting is impaired, the heart muscle can be damaged and skeletal muscles start breaking down.

Essentially, this is what we describe as multi-organ failure. People with heatstroke can die within a few hours, or several days or even weeks later from organ failure.

Protecting yourself

Heatstroke could be “exertional”, as with athletes, or “classic”, which occurs in patients with impaired thermostatic responses, as a result of age, illness or medications.

Heatstroke can be caused by exertion, such as with athletes putting their body through stress in extreme temperatures.
from shutterstock.com

Much of the increase in deaths during hotter temperatures occurs in older patients with a chronic illness. This is because they may have a poorly functioning central nervous system that cannot orchestrate the physiological changes needed to lose heat.

Older hearts may not be able to cope with the changes in circulation needed for more blood flow to go to the skin. Some medications can also interfere with the mechanisms for heat loss.

People experiencing any of the warning signs of heat stress (headache, nausea, light-headedness and fatigue) need to alter their behaviour to reduce it.

The best way to do this is to find a cool spot indoors or in the shade, put on light clothing, avoid physical exertion, put a damp cloth on your skin, immerse yourself in cold water and stay well hydrated.

But for some people, like children who are too young to make changes to their environment (such as those left in cars), this is not possible. Also, for the elderly, perhaps those with chronic mental illness or on certain medications that impair their ability to respond to increasing core temperature, these signs may not be apparent or noticed.




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Strategies for coping with extremely hot weather


This means we need safeguards to ensure the vulnerable stay cool. This is especially a problem for elderly people who live alone.

So, as our climate warms up, we need to do all we can to minimise the consequences of an increasingly hot environment. That means we must adapt our behaviour, our understanding of the issues, our urban environments, our sporting events and our systems that look out for the vulnerable in our community.


The ConversationThis article was co-authored by Dr Mark Monaghan, an emergency physician, and Dr Liz Bashford, an anaesthetist, who are both members of Doctors for the Environment Australia.

David Shearman, Emeritus Professor of Medicine, University of Adelaide

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

2017: the year in extreme weather


Andrew King, University of Melbourne

Overall 2017 will be the warmest non-El Niño year on record globally, and over the past 12 months we have seen plenty of extreme weather, both here in Australia and across the world.

Here I’ll round up some of this year’s wild weather, and look forward to 2018 to see what’s around the corner.

Drought and flooding rains… again

It feels as if Australia has had all manner of extreme weather events in 2017.
We had severe heat at both the start and end of the year. Casting our minds back to last summer, both Sydney and Brisbane experienced their hottest summers on record, while parts of inland New South Wales and Queensland endured extended periods of very high temperatures.


Read more: We’ve learned a lot about heatwaves, but we’re still just warming up


More recently Australia had an unusually dry June and its warmest winter daytime temperatures on record. The record winter warmth was made substantially more likely by human-caused climate change.

The end of the year brought more than its fair share of extreme weather, especially in the southeast. Tasmania had by far its warmest November on record, beating the previous statewide record by more than half a degree. Melbourne had a topsy-turvy November with temperatures not hitting the 20℃ mark until the 9th, but a record 12 days above 30℃ after that.

November was rounded off by warnings for very severe weather that was forecast to strike Victoria. Melbourne missed the worst of the rains, although it still had a very wet weekend on December 2-3. Meanwhile, northern parts of the state were deluged, with many places recording two or three times the December average rainfall in just a couple of days.

Hurricane after hurricane after hurricane…

Elsewhere in the world there was plenty more headline-worthy weather.

The Atlantic Ocean had a particularly active hurricane season, with several intense systems. Hurricane Harvey struck Texas and its slow trajectory resulted in record-breaking rainfall over Houston and neighbouring areas.

Then Hurricanes Irma and Maria, both of which reached the strongest Category 5 status, brought severe weather to the Caribbean and southeastern United States just a couple of weeks apart. Island nations and territories in the region are still recovering from the devastation.

Around the same time, the Indian subcontinent experienced a particularly wet monsoon season. Flooding in India, Pakistan, Bangladesh, and Nepal killed more than 1,000 people and affected tens of millions more.

Other parts of the world experienced their own severe weather events. Whether it was summer heat in Europe or wildfires in California, 2017 dished up plenty of extremes.

In many cases, especially for heat extremes, we can rapidly identify a human influence and show that climate change is increasing the frequency and intensity of such events.

For other weather types, like the very active hurricane season and other extreme rain or drought events, it is harder (but not always impossible) to work out whether it bears the fingerprint of climate change.

What’s in store for 2018?

The main problem when trying to offer an outlook is that extreme weather is hard to predict, even on the scale of days or weeks in advance, let alone months.

For Australia, with a weak La Niña in the Pacific, there are few clear indications of what the rest of the summer’s weather will bring. There is a suggestion that we can expect a slightly wetter than average start to the year in parts of the southeast, along with warmer than average conditions for Victoria and Tasmania. Beyond that it is anyone’s guess.


Read more: Not just heat: even our spring frosts can bear the fingerprint of climate change


The La Niña is also likely to mean that 2018 won’t be a record hot year for the globe. But it’s a safe bet that despite the La Niña, 2018 will still end up among the warmest years on record, alongside every other year this century. Rising global average temperatures, along with our understanding of the effect of greenhouse gas emissions, are one of our clearest lines of evidence for human-caused climate change.

The ConversationSo it’s hard to say much about what extreme weather we’ll experience in 2018, other than to say that there’s likely to be plenty more weather news to wrap up in a year’s time.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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