2,000 years of records show it’s getting hotter, faster



European heatwaves are part of a pattern of rapid global warming.
EPA/ABEL ALONSO

Ben Henley, University of Melbourne

New reconstructions of Earth’s temperature over the past 2,000 years, published today in Nature Geoscience, highlight the astonishing rate of the recent widespread warming of our planet.

We also now have a clearer picture of decade-to-decade temperature variations, and what drove those fluctuations before the industrial revolution took hold.

Contrary to previous theories that pre-industrial temperature changes in the last 2,000 years were due to variations in the Sun, our research found volcanoes were largely responsible. However, these effects are now dwarfed by modern, human-driven climate change.




Read more:
40 years ago, scientists predicted climate change. And hey, they were right


Reading the tree rings

Without networks of thermometers, ocean buoys and satellites to record temperature, we need other methods to reconstruct past climates. Luckily, nature has written the answers down for us. We just have to learn how to read them.

Corals, ice cores, tree rings, lake sediments, and ocean sediment cores provide a wealth of information about past conditions – this is called “proxy” data – and can be brought together to tell us about the global climate in the past.

Tree rings, corals and ice cores all provide ‘proxy data’ – information about changing temperatures over the centuries.
Simon Stankowski/Unsplash, CC BY

Teams of scientists around the world have spent many thousands of hours of field and laboratory work to collect and analyse samples, and ultimately publish and make available their data so other scientists can undertake further analysis.

Previously, our team, along with many other proxy experts, meticulously analysed and collated temperature-sensitive proxy data covering the last 2,000 years from around the world, creating the largest database of temperature-sensitive proxy data yet assembled. We then made all of the data publicly available in one place.

Astonishing consistency between reconstruction methods

With this unique dataset in hand, our team set about reconstructing past global temperature.

We scientists are notoriously sceptical of our own analysis. But what makes us more confident about our findings is when different methods applied to the same data yield the same result.

In this paper we applied seven different methods to reconstruct global temperature from our proxy network. We were astounded to find that the methods all gave remarkably similar results for multidecadal fluctuations – a very precise result considering the breadth of the methods used.

This gave us the confidence to delve further into what drove global temperature fluctuations on decadal timescales before the industrial revolution really took hold.

What happened before human-induced climate change?

Our study produces the clearest picture yet of Earth’s average temperature over the past two millennia. We also found that climate models performed very well in comparison, and they succeed in capturing the amount of natural variability in the climate system – the natural ups and downs in temperature from year-to-year and decade-to-decade.

Using climate models and reconstructions of external climate forcing, such as from volcanic eruptions and solar variability, we deduced that before the industrial revolution, global temperature fluctuations from decade to decade in the past 2,000 years were mainly controlled by aerosol forcing from major volcanic eruptions, not variations in the Sun’s output. Volcanic aerosols have a temporary cooling effect on the global climate. Following these temporary cooling periods our reconstructions show there is an increased probability of a temporary warming period due to the recovery from volcanic cooling.

Earlier this year One Nation leader Pauline Hanson suggested that volcanic eruptions may be responsible for the recent rise in atmospheric carbon dioxide levels.

Recent warming is far beyond natural variability

There are, of course, natural changes in Earth’s temperature from decade to decade, from century to century, and also on much longer timescales. With our new reconstructions were also able to quantify the rate of warming and cooling over the past 2,000 years. Comparing our reconstructions to recent worldwide instrumental data, we found that at no time in the last 2,000 years has the rate of warming been so high.

In statistical terms, rates of warming during all 51-year periods from the 1950s onwards exceed the 99th percentile of reconstructed pre-industrial 51 yr trends. If we look at timescales longer than 20 years, the probability that the largest warming trend occurred after 1850 greatly exceeds the values expected from chance alone. And, for trend lengths over 50 years, that probability swiftly approaches 100%. So what do all these stats mean? The strength of the recent warming is extraordinary. It is yet more evidence of human-induced warming of the planet.

But hasn’t there been natural climate change in the past?

Our understanding of past temperature variations of the Earth contributes to understanding such fundamental things as how life evolved, where our species came from, how our planet works and, now that humans have fundamentally altered it, how modern climate change will unfold.

We know that over millions of years, the movement of tectonic plates and interactions between the solid earth, the atmosphere and the ocean, have a slow effect on global temperature. On shorter (but still very long) timescales of tens to hundreds of thousands of years, our planet’s climate is gradually influenced by small variations in the geometry of the Earth and the Sun, for example, small wobbles and variations in the Earth’s tilt and orbit.

From the Last Glacial Maximum, about 26,000 years ago, when huge ice sheets covered large parts of the Northern Hemisphere landmass, Earth transitioned to a 12,000-year warm period, called the Holocene.




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Two centuries of continuous volcanic eruption may have triggered the end of the ice age


This was a time of relative stability in global temperature, apart from the temporary cooling effect of the odd volcano. With the development of human agriculture, our prosperity and population grew. Before the industrial revolution, Earth had not seen carbon dioxide concentrations above current levels for at least 2 million years.

Following the industrial revolution, warming commenced due to human activity. With a clearer picture of temperature variations over the past two millennia we now have a better understanding of the extraordinary nature of recent warming.

It is up to all of us to decide whether this is the kind of experiment we want to run on our planet.


I would like to gratefully acknowledge the leader of this study, Raphael Neukom, and my fellow co-authors from the PAGES 2k Consortium. We also owe the teams of proxy experts much gratitude. It is their generous contribution to science and to human knowledge that has allowed for this, and other palaeoclimate compilation and synthesis studies.The Conversation

Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne

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

40 years ago, scientists predicted climate change. And hey, they were right



It’s been four decades since the first credible, global report on the effect of carbon dioxide on the global climate.
Shutterstock

Neville Nicholls, Monash University

This month the world has been celebrating the 50th anniversary of Neil Armstrong setting foot on the Moon. But this week sees another scientific anniversary, perhaps just as important for the future of civilisation.

Forty years ago, a group of climate scientists sat down at Woods Hole Oceanographic Institution in Massachusetts for the first meeting of the “Ad Hoc Group on Carbon Dioxide and Climate”. It led to the preparation of what became known as the Charney Report – the first comprehensive assessment of global climate change due to carbon dioxide.




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It doesn’t sound as impressive as landing on the Moon, and there certainly weren’t millions waiting with bated breath for the deliberations of the meeting.

But the Charney Report is an exemplar of good science, and the success of its predictions over the past 40 years has firmly established the science of global warming.

What is this ‘greenhouse gas’ you speak of?

Other scientists, starting in the 19th century, had already demonstrated that carbon dioxide was what we now call a “greenhouse gas”. By the 1950s, scientists were predicting warming of several degrees from the burning of fossil fuels. In 1972 John Sawyer, the head of research at the UK Meteorological Office, wrote a four-page paper published in Nature summarising what was known at the time, and predicting warming of about 0.6℃ by the end of the 20th century.

But these predictions were still controversial in the 1970s. The world had, if anything, cooled since the middle of the 20th century, and there was even some speculation in the media that perhaps we were headed for an ice age.

The meeting at Woods Hole gathered together about 10 distinguished climate scientists, who also sought advice from other scientists from across the world. The group was led by Jule Charney from the Massachusetts Institute of Technology, one of the most respected atmospheric scientists of the 20th century.

The Report lays out clearly what was known about the likely effects of increasing carbon dioxide on the climate, as well as the uncertainties. The main conclusion of the Report was direct:

We estimate the most probable warming for a doubling of CO₂ to be near 3℃ with a probable error of 1.5℃.

In the 40 years since their meeting, the annual average CO₂ concentration in the atmosphere, as measured at Mauna Loa in Hawaii, has increased by about 21%. Over the same period, global average surface temperature has increased by about 0.66℃, almost exactly what could have been expected if a doubling of CO₂ produces about 2.5℃ warming – just a bit below their best estimate. A remarkably prescient prediction.


Author provided/The Conversation, CC BY-ND

Reception of the article

Despite the high regard in which the authors of the Charney Report were held by their scientific peers at the time, the report certainly didn’t lead to immediate changes in behaviour, by the public or politicians.

But over time, as the world has continued to warm as they predicted, the report has become accepted as a major milestone in our understanding of the consequences our actions have for the climate. The current crop of climate scientists revere Charney and his co-authors for their insight and clarity.

Strong science

The report exemplifies how good science works: establish an hypothesis after examining the physics and chemistry, then based on your assessment of the science make strong predictions. Here, “strong predictions” means something that would be unlikely to come true if your hypothesis and science were incorrect.

In this case, their very specific prediction was that warming of between 1.5℃ and 4.5℃ would accompany a doubling of atmospheric CO₂. At the time, global temperatures, in the absence of their hypothesis and science, might have been expected to stay pretty much the same over the ensuing 40 years, cooled a bit, possibly even cooled a lot, or warmed a lot (or a little).

In the absence of global warming science any of these outcomes could have been feasible, so their very specific prediction made for a very stringent test of their science.

The Charney Report’s authors didn’t just uncritically summarise the science. They also acted sceptically, trying to find factors that might invalidate their conclusions. They concluded:

We have tried but have been unable to find any overlooked or underestimated physical effects that could reduce the currently estimated global warmings due to a doubling of atmospheric CO₂ to negligible proportions or to reverse them altogether.

The report, and the successful verification of its prediction, provides a firm scientific basis for the discussion of what we should do about global warming.

Over the ensuing 40 years, as the world warmed pretty much as Charney and his colleagues expected, climate change science improved, with better models that included some of the factors missing from their 1979 deliberations.




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This subsequent science has, however, only confirmed the conclusions of the Charney Report, although much more detailed predictions of climate change are now possible.The Conversation

Neville Nicholls, Professor emeritus, School of Earth, Atmosphere and Environment, Monash University

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

The waterwheel plant is a carnivorous, underwater snap-trap



The whaterwheel plant can snap up its prey in milliseconds.
The Conversation

Adam Cross, Curtin University

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


Billabongs in the northern Kimberley are welcome oases of colour in an otherwise brown landscape. This one reflected the clear blue sky, broken up by water lilies and a scattering of yellow Nymphoides flowers. A ring of trees surrounded it, taking advantage of the permanent water source.

My student and I approached with excitement. We had spent a week searching barren habitats, but now on the final day of our expedition we were ecstatic about the potential of this watering hole.




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The strange world of the carnivorous plant


Between us we had been plant-hunting in northern Australia for nearly 20 years and knew well that where water seeped over sandstone, carnivorous plants often grew.

Hunting carnivorous plants in the North Kimberley.
Adam Cross, Author provided

Clambering along some rocks at the edge of the billabong, I looked down by chance into a small rockhole and nearly fell in. Floating between two water lily leaves was a short stem of whorled leaves. And at the end of each leaf, a tiny snapping trap.

Looking out into the middle of the billabong I saw thousands of plants, and even a few tiny white flowers protruding above the surface of the water. After a decade of fruitlessly searching the swamps, creeks and rivers of the Kimberley for it, I had stumbled across a new population of Aldrovanda vesiculosa, the waterwheel plant.



The Conversation

The waterwheel plant must surely be among the most fascinating plants in the world. Its genus dates back 50 million years, and although we know of many species from the fossil record, A. vesiculosa is the only modern species.

The waterwheel plant is a submerged aquatic plant, first discovered by botanists in 1696 and studied by the likes of Charles Darwin, and is the only species to have evolved snap-trap carnivory under water. It takes just 100 milliseconds for the snapping leaves to close upon small, unsuspecting aquatic invertebrates such as mosquito larvae – one of the fastest movements in the plant kingdom.

Although the waterwheel plant also photosynthesises, it needs to eat prey to get enough nutrients to grow. And while its traps may be small, up to 1cm long, it can efficiently catch tiny insects and even small fish and tadpoles.

Mr Worldwide

Uniquely, the waterwheel plant is a global clone, with virtually no genetic differentiation between populations on different continents.

It has one of the largest and most disconnected distributions of any flowering species, growing in more than 40 countries across four continents, from sub-Arctic regions of northern Russia to the southern coast of Australia, and from western Africa to the eastern coast of Australia. Yet despite this global distribution, the waterwheel plant occupies a very small ecological niche, and grows only in the shallow and acidic waters of nutrient-poor freshwater swamps.

The waterwheel plant is sensitive, and is often the first species to disappear when these habitats become degraded.

As a result, this unique species has undergone a catastrophic global decline as humans have systematically degraded and destroyed nearly two-thirds of the world’s wetland habitats.

The past century has seen the systematic extinction of the waterwheel plant from more than half the countries it once occupied, and a rapid deterioration in almost all others. From more than 400 populations recorded since the 18th century, fewer than 50 now remain.

Three-quarters of these are in the exclusion zone surrounding the Chernobyl nuclear disaster site, with the rest spread thinly across Africa, Australia and Europe, and isolated from each other by thousands, and sometimes tens of thousands, of kilometres. The species can be seen as a harbinger of the perilous state of our world’s freshwater ecosystems.

Waterwheel plants flourish in this oasis in the remote North Kimberley.
Adam Cross, Author provided

Conservation

Ecologists are working hard at conserving the waterwheel plant: monitoring habitats, reintroducing it into areas where it has become extinct and detailed study of its ecology and reproductive biology.

But ultimately, its future depends on the survival of wetlands – complex and sensitive ecosystems that can be affected by even small changes throughout their catchment area. Wetlands are often linked together by waterbirds and other animals that disperse plant seeds and spores between them, so the degradation of one area can have significant knock-on effects even for distant locations.




Read more:
Why a wetland might not be wet


Without concerted wetland conservation, individual conservation for species like the waterwheel plant become little more than band-aids.

For the waterwheel plant, a single isolated population in a remote and untouched corner of the North Kimberley could represent a crucial refuge. It gives a thin sliver of hope that this remarkable species will still exist for future generations to marvel at.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Adam Cross, Research Fellow, Curtin University

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

More than 28,000 species are officially threatened, with more likely to come



A giant guitarfish caught in West Papua is hung from a fishing boat. Guitarfish are in trouble, according to the IUCN Red List.
Conservation International/Abdy Hasan, Author provided

Peter Kyne, Charles Darwin University

More than 28,000 species around the world are threatened, according to the Red List of Threatened Species compiled by the International Union for the Conservation of Nature (IUCN). The list, updated on Thursday night, has assessed the extinction risk of almost 106,000 species and found more than a quarter are in trouble.

While recent headline-grabbing estimates put as many as 1 million species facing extinction, these were based on approximations, whereas the IUCN uses rigorous criteria to assess each species, creating the world-standard guide to biodiversity extinction risk.




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In this update, 105,732 species were ranked from least concern (little to no risk of extinction), to critically endangered (an extremely high risk of extinction) and extinct (the last individual of a species has expired).

This Red List update doesn’t hold a lot of good news. It takes the total number of threatened species to 28,338 (or 27% of those assessed) and logs the extinction of 873 species since the year 1500.

These numbers seem small when thinking about the estimated 1 million species at risk of extinction, but only around 1% of the world’s animals, fungi and plants have been formally assessed on the IUCN Red List. As more species are assessed, the number of threatened species will no doubt grow.

More than 7,000 species from around the world were added to the Red List in this update. This includes 501 Australian species, ranging from dragonflies to fish.

The shortfin eel (Anguilla australis) has been assessed as near threatened due to poor water and river management, land clearing, nutrient run-off, and recurring drought.

The Australian shortfin eel is under threat from drought and land clearing.

Twenty Australian dragonflies were also assessed for the first time, including five species with restricted ranges under threat from habitat loss and degradation. Urban and mining expansion pose serious threats to the western swiftwing (Lathrocordulia metallica), which is only found in Western Australia.

Plight of the rhino rays

I coordinate shark and ray Red List assessments for the IUCN. Of particular concern in this update is the plight of some unique and strange fishes: wedgefishes and giant guitarfishes, collectively known as “rhino rays”.

This group of shark-like rays, which range from Australia to the Eastern Atlantic, are perilously close to extinction. All six giant guitarfishes and nine out of 10 wedgefishes are critically endangered.

Bottlenose wedgefish in Raja Ampat, Indonesia.
Credit: Arnaud Brival

While rhino ray populations are faring comparatively well in Australia, this is not the case throughout their wider Indo-Pacific and, in some cases, Eastern Atlantic ranges, where they are subject to intense and often unregulated exploitation.

The predicament of rhino rays is driven by overfishing for meat and their valuable fins. Their meat is often eaten or traded locally and, along with other sharks, rays and bony fishes, is an important part of coastal livelihoods and food security in tropical countries. Their fins are traded internationally to meet demand for shark fin soup. The “white fins” of rhino rays are highly prized in the trade and can fetch close to US$1,000 per kilogram.




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This exploitation for a high-value yet small body part places the rhino rays in the company of the rhinoceroses in more than name alone.

Bottlenose wedgefish in the Kota Kinabalu fish market in Malaysia.
Peter Kyne

Two species in particular may be very close to extinction. The clown wedgefish (Rhynchobatus cooki) from the Indo-Malay Archipelago has been seen only once in over 20 years – when a local researcher photographed a dead specimen in a Singapore fish market.

The false shark ray (Rhynchorhina mauritaniensis) is known from only one location in Mauritania in West Africa, and there have been no recent sightings. It’s likely increased fishing has taken a serious toll; the number of small fishing boats in Mauritania has risen from 125 in 1950 to nearly 4,000 in 2005.

This rising level of fishing effort is mirrored in the tropical nations of the Indo-West Pacific where most rhino rays are found.

Effective rhino ray conservation will require a suite of measures working in concert: national species protection, habitat management, bycatch reduction and international trade restrictions. These are not quick and easy solutions; all will be dependent on effective enforcement and compliance.




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The challenges of saving rhino rays illustrate the larger, mammoth task of tackling our current extinction crisis. But the cost of inaction is even larger: precipitous loss of biodiversity and, eventually, the collapse of the ecosystems on which we depend.


This article was co-written by Caroline Pollock, Program Officer for the IUCN’s Red List Unit.The Conversation

Peter Kyne, Senior Research Fellow in conservation biology, Charles Darwin University

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

Drought and climate change are driving high water prices in the Murray-Darling Basin


Neal Hughes, Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES)

Water prices in the southern Murray-Darling Basin have reached their highest levels since the worst of the Millennium drought more than a decade ago. These high water prices are causing much anxiety in the region, and have led the federal government to call on the Australian Competition and Consumer Commission to hold an inquiry into the water market.

Inevitably, whenever an important good becomes more expensive – be it housing, electricity or water – there is a rush to identify potential causes and culprits. In the past few years high water prices have been blamed on foreign investors, corporate speculators, state government water-sharing rules, new almond plantings and the Murray-Darling Basin Plan.




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While some of these factors have had an effect on the market, they are in many ways a distraction from the simpler truth: that high water prices have mostly been caused by a lack of rain.

Supply drives the market

The waters of the northern basin run to the Darling River and the waters of the southern basin run to the Murray River.
MDBA

Market reforms in the 1980s and 1990s enabled water trading in many parts of Australia. By far the most active market exists in the southern Murray-Darling basin, which covers the Murray River and its tributaries in northern Victoria, southern New South Wales and eastern South Australia.

The market allows users – mostly irrigation farmers – to trade their water allocations (effectively shares of water in the rivers’ major dams). This trading helps ensure limited water supplies go to the farmers who value them the most, which can be crucial in times of drought.

Historical data shows the main driver of water market prices in the southern basin is change in water supply.

The following chart shows storage volumes (in orange) and water prices (in red) in the southern basin since 2006. Prices peaked at the height of the Millennium drought in 2007. During the floods of 2011, they fell near zero. Prices have increased again during the latest drought, and are now at their highest levels in a decade.


Water allocation prices and storage volumes in the southern Murray-Darling Basin.
State government trade registers, BOM, Ruralco Water, ABARES estimates.

Lower rainfall, higher temperatures

While water prices have always been higher in dry years and lower in wet, we’ve been getting a lot more dry years in recent decades.

Over the past 20 years, rainfall, run-off and stream flow in the southern basin has been far less than historical conditions.

The below chart shows modelled flow data for the Murray River, assuming historical weather conditions and no water extraction, over the past century. It shows that average water flows this century are about 40% below the average of the 20th century.


Modelled ‘without-development’ annual Murray River flow, 1900 to 2018.
Murray-Darling Basin Authority.

We know these reductions are at least partly related to climate change, driven by both reduced winter rainfall and higher temperatures.

Lower rainfall and higher temperatures also make crops thirstier, increasing demand for irrigation water. This was evident in January, when temperatures exceeded 35℃ for 14 days and irrigators’ demand for water spiked from about 4.5 gigalitres to 7 gigalitres a day.




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The basin plan in perspective

The Murray-Darling Basin Plan seeks to improve the environmental health of the river system by recovering water rights from irrigation farmers. To date, more than 1,700 gigalitres of water rights – about 20% of annual water supply – have been recovered in the southern basin.

By reducing supply, water recovery was always expected to increase water prices. However, the effects of water recovery on supply – while significant – are still small relative to the effects of climate over the same period, as shown in the below chart.


Water allocation use in the southern basin with and without water recovery.
State government agencies, Department of Agriculture, ABARES estimates.

Measuring the precise effect of water recovery on prices is difficult. Water buybacks are straightforward and have been modelled by ABARES and others. But the effects of infrastructure programs – where farmers return a portion of their water rights in exchange for funding to upgrade infrastructure – are harder to estimate.




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Billions spent on Murray-Darling water infrastructure: here’s the result


‘Carryover’ rule changes

Historically farmers had to use water allocations within a 12-month window. The introduction of “carryover” – most recently in Victoria in 2008 – means users can now hold their unused water in dams. This rule change was a good thing, as it encourages farmers to conserve water and build up a buffer against drought.

But it might also have contributed to anxiety about the water market’s operations.

Since water allocations can be bought and held for multiple years, information about future conditions can have a big effect on prices now. For example, we see large jumps in price following news of worse-than-expected supply forecasts. This may have helped fuel concern about “speculators”.

Over the longer-term, the ability to store water helps to “smooth” water prices, with slightly higher prices in most years offset by much lower prices in drought years. Again this is a good thing, but it may have added to the perception of higher prices in the market.

Water demand is rising

When a profitable new irrigation activity is willing to pay more for water – as is the case with almond farms in the southern basin – competition for limited supplies can potentially drive up prices.

ABARES’ research shows that between 2003 and 2016 there was little change in irrigation demand (aside from that linked to rainfall). Growth in demand from expanding activities such as almonds and cotton was offset by reductions in others including dairy, rice and wine grapes. However, there is evidence since 2016 that demand for water has started to increase, contributing to higher water prices. Longer-term projections suggest this trend may continue.

With drought and climate change reducing water supply, and demand for both environmental and irrigation water increasing, high water prices are only likely to become more common in the basin in future.The Conversation

Neal Hughes, Senior Economist, Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES)

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

Taller, faster, better, stronger: wind towers are only getting bigger



Wind towers are getting taller.
Shutterstock

Con Doolan, UNSW

Former Australian Greens leader Bob Brown made headlines this week after he objected to a proposed wind farm on Tasmania’s Robbins Island. The development would see 200 towers built, each standing 270 metres from base to the tip of their blades.

Leaving aside the question of the Robbins Island development, these will be extraordinarily tall towers. However, they fit right in with the current trend for wind turbines.




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Wind turbines come in many designs, but the most common is the so-called “horizontal axis” kind, which look like giant fans on poles. This type of turbine is highly efficient at turning the energy in the wind into electrical energy.

Keen observers will have noticed that these turbines have been gaining in size over the years. In the 1990s, wind turbines typically had hub heights and rotor diameters of the order of 30m. Today, hub heights and rotor diameters are pushing well past 100m.



Shutterstock/The Conversation

Bigger is better

When it comes to wind turbines, bigger is definitely better. The bigger the radius of the rotor blades (or diameter of the “rotor disc”), the more wind the blades can use to turn into torque that drives the electrical generators in the hub. More torque means more power. Increasing the diameter means that not only more power can be extracted, but it can be done so more efficiently.

Larger and longer turbine blades mean greater aerodynamic efficiency. Creating more power in one turbine means less energy is lost as it is moved into the transmission system, and from there into the electrical generator. The economies of scale provide an overwhelming push for wind energy companies to develop larger rotor blades.




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Wind turbines are also growing taller because of the way wind travels around the world. Because air is viscous (like very thin honey) and “sticks” to the ground, the wind velocity at higher altitudes can be many times higher than at ground level.

Hence it is advantageous to put the turbine high in the sky where there is more energy to extract. Hilly terrain (like a mountain ridge) may also distort the wind, requiring engineers to design the wind turbines to be even taller to catch the wind. Wind turbines used offshore are generally larger and taller because of the higher levels of wind energy available at sea.

Typically, onshore turbines (most common in Australia) have blades between 40m and 90m long. Tower heights are usually in the range of 150m. Offshore turbines (those situated at sea and common in Europe) are much larger.

Offshore turbines are typically much larger than onshore towers.
Shutterstock

One of the largest wind turbine designs in the world, General Electric’s offshore 12-megawatt Haliade-X, has 107m blades and a total height of 260m. As a comparison, Sydney’s Centrepoint tower is 309m tall.

If the Robbins Island turbines are indeed built to 270m, as reported in the media, they would eclipse General Electric’s behemoths. I cannot speak to the likelihood of this, but I would assume engineers will have to select the best turbine for the prevailing wind conditions and existing infrastructure.

Challenging heights

The quest for bigger and taller turbines comes with its fair share of engineering challenges.

Longer blades are more flexible than shorter ones, which can create vibration. If not controlled, this vibration affects performance and reduces the life of the blades and anything they are attached to, such as the gearbox or generator.

Materials and manufacturing techniques are constantly being refined to create longer, and longer-lasting, turbine blades.

The longer the turbine’s blades, the more pressure is put on internal mechanisms.
Shutterstock

Taller turbines generate more power, which puts greater loads on the gearbox and transmission system, requiring mechanical engineers to develop new ways of converting the ever-increasing torque into electrical power. Taller wind turbines also need stronger support towers and foundations. The list of challenges is long.

As turbines grow, so too does the noise they make. The dominant source of noise occurs at the outer edge of the blades. Here, turbulence caused by the blade itself creates a “hissing” sound as it passes over the trailing edge. More noise is created when the blade chops through atmospheric turbulence in the wind as it blows into the tower.

Noise isn’t just a matter of size. If one turbine is placed in the wake of another, the sound of its blades passing through the highly turbulent air created by the upstream turbine will be very loud.

Keeping noise under control requires inventive solutions, such as borrowing ideas from nature: the silent-flying owl uses serrated feathers to control noise and these are now being used to make noisy turbines quieter.




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Of course, engineering challenges are not the only considerations for creating wind farms. Environmental effects, noise, visual impacts and other community concerns all need to be considered, as with any large infrastructure project. But wind turbines are one of the most cost-effective and technologically sophisticated forms of renewable energy, and as the developed world comes to grips with climate change we will only see more of them.The Conversation

Con Doolan, Professor, School of Mechanical and Manufacturing Engineering, UNSW

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