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ARENA’s large-scale solar funding round revealed projected connection costs noticeably lower than for existing projects. Why is it so?

Three battalions ready to avert crisis after storms last year caused severe damage across north of England

Theresa May has placed three battalions of up to 1,200 soldiers on 24-hour standby to help if England suffers flooding this winter.

Last winter torrential rain affected thousands of families, resulting in criticism of the government. The storms forced the evacuation of homes and caused severe damage across the north of England. Somerset was badly affected by floods a year earlier.

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After a small celebration of COP21 achievements, COP22 gets down to business on accountability, as report reveals a shortfall between Paris commitments and the pre-Paris indicative commitments such as Australia’s 2030 target.

NSW government's draft energy plans take an ambitious, integrated approach to both renewables and energy efficiency – and that's a big deal for two major reasons.

PLANT POWER: The rate of growth in atmospheric carbon dioxide has slowed due to an increased uptake of the greenhouse gas by the planet's plants, a new study has suggested.

Residents in Florida are being asked to vote on a trial of genetically modified mosquitoes on US Election Day.

Legislation to be trialled at Lighthouse beach, Sharpes beach and Shelly beach at Ballina, Seven Mile beach at Lennox Head and Evans Head beach

Five New South Wales beaches will soon be trialling mesh shark nets under legislation to be fast-tracked into parliament.

The legislation will be tabled by the NSW primary industries minister, Niall Blair, on Wednesday.

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The great grey owl is imperiled by intensive logging of northern-hemisphere forests. Copyright Ondrej Prosicky/Shutterstock.

Life has existed on Earth for roughly 3.7 billion years. During that time we know of five mass extinction events — dramatic episodes when many, if not most, life forms vanished in a geological heartbeat. The most recent of these was the global calamity that claimed the dinosaurs and myriad other species around 66 million years ago.

Growing numbers of scientists have asserted that our planet might soon see a sixth massive extinction — one driven by the escalating impacts of humanity. Others, such as the Swedish economist Bjørn Lomborg, have characterised such claims as ill-informed fearmongering.

We argue emphatically that the jury is in and the debate is over: Earth’s sixth great extinction has arrived.

Collapse of biodiversity

Mass extinctions involve a catastrophic loss of biodiversity, but what many people fail to appreciate is just what “biodiversity” means. A shorthand way of talking about biodiversity is simply to count species. For instance, if a species goes extinct without being replaced, then we are losing biodiversity.

But there’s much more to biodiversity than just species. Within each species there usually are substantial amounts of genetic, demographic, behavioural and geographic variation. Much of this variation involves adaptations to local environmental conditions, increasing the biological fitness of the individual organism and its population.

Natural variation within two species of sea snails. Upper row: Littorina sitkana. Lower row: Littorina obtusata. Copyright David Reid/Ray Society.

And there’s also an enormous amount of biodiversity that involves interactions among different species and their physical environment.

Many plants rely on animals for pollination and seed dispersal. Competing species adapt to one another, as do predators and their prey. Pathogens and their hosts also interact and evolve together, sometimes with remarkable speed, whereas our internal digestive systems host trillions of helpful, benign or malicious microbes.

Hence, ecosystems themselves are a mélange of different species that are continually competing, combating, cooperating, hiding, fooling, cheating, robbing and consuming one another in a mind-boggling variety of ways.

All of this, then, is biodiversity - from genes to ecosystems and everything in between.

The modern extinction spasm Cumulative vertebrate species extinctions since 1500 compared to the ‘background’ rate of species losses. G. Ceballos et al. (2015) Scientific Advances.

No matter how you measure it, a mass extinctions has arrived. A 2015 study that one of us (Ehrlich) coauthored used conservative assumptions to estimate the natural, or background rate of species extinctions for various groups of vertebrates. The study then compared these background rates to the pace of species losses since the beginning of the 20th century.

Even assuming conservatively high background rates, species have been disappearing far faster than before. Since 1900, reptiles are vanishing 24 times faster, birds 34 times faster, mammals and fishes about 55 times faster, and amphibians 100 times faster than they have in the past.

For all vertebrate groups together, the average rate of species loss is 53 times higher than the background rate.

Extinction filters

To make matters worse, these modern extinctions ignore the many human-caused species losses before 1900. It has been estimated, for instance, that Polynesians wiped out around 1,800 species of endemic island birds as they colonised the Pacific over the past two millennia.

And long before then, early human hunter-gatherers drove a blitzkrieg of species extinctions — especially of megafauna such as mastodons, moas, elephant birds and giant ground sloths — as they migrated from Africa to the other continents.

In Australia, for instance, the arrival of humans at least 50,000 years ago was soon followed by the disappearance of massive goannas and pythons, predatory kangaroos, the marsupial “lion”, and the hippo-sized Diprotodon among others.

Changes in climate could have contributed, but humans with their hunting and fires were almost certainly the death knell for many of these species.

As a result of these pre-1900 extinctions, most ecosystems worldwide went through an “extinction filter”: the most vulnerable species vanished, leaving relatively more resilient or less conspicuous species behind.

Giant ground sloths such as this elephant-sized Megatherium vanished soon after humans arrived in the New World. Copyright Catmando.

And it’s the loss of these survivors that we are seeing now. The tally of all species driven to extinction by humans from prehistory to today would be far greater than many people realise.

Vanishing populations

The sixth great extinction is playing out in other ways too, especially in the widespread annihilation of millions (perhaps billions) of animal and plant populations. Just as species can go extinct, so can their individual populations, reducing both the genetic diversity and long-term survival prospects of the species.

For example, the Asian two-horned rhinoceros once ranged widely across Southeast Asia and Indochina. Today it survives only in tiny pockets comprising perhaps 3% of its original geographic range.

Three-quarters of the world’s largest carnivores, including big cats, bears, otters and wolves, are declining in number. Half of these species have lost at least 50% of their former range.

Likewise, except in certain wilderness areas, populations of large, long-lived trees are falling dramatically in abundance.

WWF’s 2016 Living Planet Report summarises long-term trends in over 14,000 populations of more than 3,700 vertebrate species. Its conclusion: in just the last four decades, the population sizes of monitored mammals, birds, fish, amphibians and reptiles have shrunk by an average of 58% worldwide.

And as populations of many species collapse, their crucial ecological functions decline with them, potentially creating ripple effects that can alter entire ecosystems.

Hence, disappearing species can cease to play an ecological role long before they actually go extinct.

Once a widespread and dominating predator, the tiger today is vanishingly rare across most of its former range. Copyright Matt Gibson Paying the extinction debt

Everything we know about conservation biology tells us that species whose populations are in freefall are increasingly vulnerable to extinction.

Extinctions rarely happen instantly, but the conspiracy of declining numbers, population fragmentation, inbreeding and reduced genetic variation can lead to a fatal “extinction vortex”. In this sense, our planet is currently accumulating a large extinction debt that must eventually be paid.

And we’re not just talking about losing cute animals; human civilisation relies on biodiversity for its very existence. The plants, animals and microorganisms with which we share the Earth supply us with vital ecosystem services. These include regulating the climate, supplying clean water, limiting floods, running nutrient cycles essential to agriculture and forestry, controlling serious crop pests and carriers of diseases, and providing beauty, spiritual and recreational benefits.

Are we preaching doom? Far from it. What we’re saying, however, is that life on Earth is ultimately a zero-sum game. Humans cannot keep growing in number and consuming ever more land, water and natural resources and expect all to be well.

Limiting harmful climate change has become a catchphrase for battling such maladies. But solutions to the modern extinction crisis must go well beyond this.

We also have to move urgently to slow human population growth, reduce overconsumption and overhunting, save remaining wilderness areas, expand and better protect our nature reserves, invest in conserving critically endangered species, and vote for leaders who make these issues a priority.

Without decisive action, we are likely to hack off vital limbs of the tree of life that could take millions of years to recover.

The Slow Loris, a primitive primate, is a denizen of intact rainforests in southern Asia. Copyright hkhtt hj

Paul Ehrlich will present a lecture on the current mass extinction, at James Cook University’s Cairns campus on November 10.

Bill Laurance receives funding from the Australian Research Council and other scientific and philanthropic organisations. He is the director of the JCU Centre for Tropical Environmental and Sustainability Science, and founder and director of ALERT--the Alliance of Leading Environmental Researchers & Thinkers.

Paul Ehrlich does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

The Millennium drought had a huge impact on the Murray-Darling river system. suburbanbloke/Flickr/Wikimedia Commons, CC BY-SA

The journal Climatic Change has published a special edition of review papers discussing major natural hazards in Australia. This article is one of a series looking at those threats in detail.

Droughts are a natural feature of the Australian environment. But the Millennium drought (or “Big Dry”), which ran from 1997 to 2010, was a wake-up call even by our parched standards.

The Millennium drought had major social, economic and environmental impacts. It triggered water restrictions in major cities, and prompted severe reductions in irrigation allocations throughout the vast Murray-Darling Basin.

The Millennium drought also highlighted that, compared to the rest of the world, the impacts of drought on Australia’s society and economy are particularly severe. This is mainly because our water storage and supply systems were originally designed by European settlers who failed to plan for the huge variability in Australia’s climate.

Have we learned the lessons?

Are we likely to fare any better when the next Big Dry hits? It’s important to reflect on how much we actually understand drought in Australia, and what we might expect in the future.

Our study, part of the Australian Water and Energy Exchanges Initiative (OzEWEX), had two aims related to this question. The first was to document what is known and unknown about drought in Australia. The second aim was to establish how Australia’s scientists and engineers can best investigate those unknowns.

The fact is that despite their significance, droughts are generally still poorly understood. This makes it hard to come up with practical, effective strategies for dealing with them when they strike.

One reason for this is that unlike natural hazards with more graphic and measurable impacts (such as floods, cyclones, and bushfires), droughts develop gradually over huge areas, and can last for years. Often they go unnoticed until they trigger widespread water or food shortages, or cause significant energy, economic, health or environmental issues.

By the time you know it’s arrived, a drought can already be doing damage. Bidgee/Wikimedia Commons, CC BY-SA

Drought has been described as a “creeping disaster”, because by the time a drought is identified, it is usually already well under way, the costs to fix it are mounting, and the opportunity to take proactive action has already been missed.

This is complicated still further by the uncertainties around defining, monitoring and forecasting drought – including predicting when a drought will finally end. As in the case of other natural hazards (such as drought’s polar opposite, floods), what we need most is accurate and practically useful information on the likelihood, causes and consequences of droughts in particular areas.

This is a very tricky question, not least because we still need to come up with a rigorous way to distinguish between correlation and causation. For example, are increased local temperatures a cause or a consequence of drought?

The complications don’t end there. Because droughts are so much slower and bigger than other natural disasters, they therefore have much more complicated effects on agriculture, industry and society. Bushfires can be devastating, but they also offer ample opportunities to learn lessons for the next time. Droughts, in contrast, give us limited opportunities to learn how best to prepare.

Yet prepare we must. Given Australia’s history of decades-long swings between wet and dry, and the fact that these swings are projected to grow even stronger, drought will be a key concern for Australia for a long time to come.

What to do next

We therefore make several recommendations to help boost our understanding and management of drought.

1). Reconsider the way drought is defined and monitored to remove confusion between drought causes, impacts and risks. Similarly, there is also a need to better distinguish between drought, aridity, and water scarcity due to over-extractions.

The simplest definition of “drought” is a deficit of water compared with normal conditions. But what is normal? How long does the deficit have to persist, and how severe does it need to be, to be considered a drought? What is meant by water: rainfall, snow, ice, streamflow, water in a storage reservoir, groundwater, soil moisture, or all of these?

The answers to these questions depend very much on the local situation in terms of climate and water use, which varies significantly in space and time and is why the simplest definition of drought is insufficient. We need to develop drought definitions that clearly differentiate drought from long-term changes in aridity and water scarcity, and that capture drought start, duration, magnitude and spatial extent. Such definitions should account for the differences between Australia’s climate zones, the wide variety of end-users and applications of drought monitoring information, and the diversity of droughts that have occurred in the past. There needs to be a common understanding of what a drought is and the differences between drought, aridity and human-induced water scarcity.

2). Improve documentation of droughts that took place before weather records began, in roughly 1900. This will improve our understanding of Australia’s long-term “baseline” drought characteristics (that is, how bad can droughts get? how does the worst drought on record compare with the worst that has ever occurred?), and thus provide the fundamental information needed to successfully manage droughts.

This requires compilation of longer-term and more spatially complete drought histories via the merging of palaeoclimate information with instrumental, satellite, and reanalysis data. This will help us better understand instrumental and pre-instrumental drought behaviour, and put the droughts observed in the instrumental record into context. This work will involve looking at ice cores, tree rings, different tree rings, cave deposits, corals, sediments and historical changes to river channels and floodplains.

3). Improve drought forecasting by developing more realistic models of the many factors that cause (or contribute to) drought. This will help us separate out the influences of natural variability and human-induced climate change, which in turn will help us make more accurate long-term projections.

If we can answer these big research questions, we will all be better prepared when the next big dry inevitably arrives.

Anthony Kiem receives funding from the Australian Research Council and the National Climate Change Adaptation Research Facility.

Fiona Johnson receives funding from the Australian Research Council and World Health Organisation.

Seth Westra receives funding from the Australian Research Council and various State Government research funding programs.

The growth in CO2 in the atmosphere has been slowed by the increased ability of plants to soak up the gas.

Proposal to cut emissions controversially emits several appliances on the grounds that economic benefits would not be worth the negative publicity

The EU has dropped plans to force toaster-makers to improve the energy efficiency of their products over fears of the political costs of being seen to be intruding in people’s daily lives, it has emerged.

But while a new EU plan to cut emissions controversially emits several appliances, the manufacturers of electric kettles, refrigerators and hand driers will have to make their future products consume less energy.

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The World Meteorological Organisation (WMO) says that the five years from 2011 to 2015 were the warmest on record.

Increased growth of plants fertilised by higher CO2 levels is only partly offsetting emissions and will not halt dangerous warming, scientists conclude

A global “greening” of the planet has significantly slowed the rise of carbon dioxide in the atmosphere since the start of the century, according to new research.

More plants have been growing due to higher CO2 levels in the air and warming temperatures that cut the CO2 emitted by plants via respiration. The effects led the proportion of annual carbon emissions remaining in the air to fall from about 50% to 40% in the last decade.

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Land Speed Record holder Andy Green has been celebrating the work done in Northern Cape, South Africa, to prepare the fastest ever race car track.

As a huge crater opened up in the Japanese city of Fukuoka this morning, we take a look at the largest urban sinkholes – from Guangzhou to Guatemala City

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Dry summer, tighter regulations and more spending by water companies sees 98.5% of beaches monitored by the Environment Agency meet EU standards

England’s bathing waters are the cleanest ever recorded thanks to a dry summer, tighter EU regulations and increased spending by water companies.

Of the 413 beaches monitored up to 20 times a year by the Environment Agency for their pollution, 98.5% passed the minimum EU limit. Of these, 69% were rated “excellent” and 27% “good”. Water at five persistently failing beaches met the minimum standard for the first time, but six beaches failed.

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A public appeal to find a second rare left-coiled snail succeeds

Waltham Brooks, West Sussex The bird bobs its squat body up and down, then launches low across the water, the light catching its shimmering back

The still pool reflects the blue sky. The kingfisher sits in the low willow branch. It flicks its tail up and down, up and down, like a switch, while it looks down, transfixed by something in the water below. It suddenly blurs into movement, there’s a splash, and the colourful missile returns to its perch with a tiny silver fish in its bill. It bashes the minnow on the branch twice, and swallows it.

Related: Kingfisher bonds will loosen as summer fades

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Success in Marrakesh will be difficult, as grunt work on rulemaking replaces the diplomatic showmanship of last year's Paris climate talks.

US Senate control is in the hands of 8 key states, only two of which will have a senator who accepts climate science.