What is a ‘mass extinction’ and are we in one now?



Humans are probably causing what ice ages and asteroids caused before them.
Keith Roper/Flickr, CC BY-SA

Frédérik Saltré, Flinders University and Corey J. A. Bradshaw, Flinders University

For more than 3.5 billion years, living organisms have thrived, multiplied and diversified to occupy every ecosystem on Earth. The flip side to this explosion of new species is that species extinctions have also always been part of the evolutionary life cycle.

But these two processes are not always in step. When the loss of species rapidly outpaces the formation of new species, this balance can be tipped enough to elicit what are known as “mass extinction” events.




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A mass extinction is usually defined as a loss of about three quarters of all species in existence across the entire Earth over a “short” geological period of time. Given the vast amount of time since life first evolved on the planet, “short” is defined as anything less than 2.8 million years.

Since at least the Cambrian period that began around 540 million years ago when the diversity of life first exploded into a vast array of forms, only five extinction events have definitively met these mass-extinction criteria.

These so-called “Big Five” have become part of the scientific benchmark to determine whether human beings have today created the conditions for a sixth mass extinction.

An ammonite fossil found on the Jurassic Coast in Devon. The fossil record can help us estimate prehistoric extinction rates.
Corey Bradshaw, Author provided

The Big Five

These five mass extinctions have happened on average every 100 million years or so since the Cambrian, although there is no detectable pattern in their particular timing. Each event itself lasted between 50 thousand and 2.76 million years. The first mass extinction happened at the end of the Ordovician period about 443 million years ago and wiped out over 85% of all species.

The Ordovician event seems to have been the result of two climate phenomena. First, a planetary-scale period of glaciation (a global-scale “ice age”), then a rapid warming period.

The second mass extinction occurred during the Late Devonian period around 374 million years ago. This affected around 75% of all species, most of which were bottom-dwelling invertebrates in tropical seas at that time.

This period in Earth’s past was characterised by high variation in sea levels, and rapidly alternating conditions of global cooling and warming. It was also the time when plants were starting to take over dry land, and there was a drop in global CO2 concentration; all this was accompanied by soil transformation and periods of low oxygen.

To establish a ‘mass extinction’, we first need to know what a normal rate of species loss is.
from http://www.shutterstock.com

The third and most devastating of the Big Five occurred at the end of the Permian period around 250 million years ago. This wiped out more than 95% of all species in existence at the time.

Some of the suggested causes include an asteroid impact that filled the air with pulverised particle, creating unfavourable climate conditions for many species. These could have blocked the sun and generated intense acid rains. Some other possible causes are still debated, such as massive volcanic activity in what is today Siberia, increasing ocean toxicity caused by an increase in atmospheric CO₂, or the spread of oxygen-poor water in the deep ocean.

Fifty million years after the great Permian extinction, about 80% of the world’s species again went extinct during the Triassic event. This was possibly caused by some colossal geological activity in what is today the Atlantic Ocean that would have elevated atmospheric CO₂ concentrations, increased global temperatures, and acidified oceans.

The last and probably most well-known of the mass-extinction events happened during the Cretaceous period, when an estimated 76% of all species went extinct, including the non-avian dinosaurs. The demise of the dinosaur super predators gave mammals a new opportunity to diversify and occupy new habitats, from which human beings eventually evolved.

The most likely cause of the Cretaceous mass extinction was an extraterrestrial impact in the Yucatán of modern-day Mexico, a massive volcanic eruption in the Deccan Province of modern-day west-central India, or both in combination.



The Conversation, CC BY-ND

Is today’s biodiversity crisis a sixth mass extinction?

The Earth is currently experiencing an extinction crisis largely due to the exploitation of the planet by people. But whether this constitutes a sixth mass extinction depends on whether today’s extinction rate is greater than the “normal” or “background” rate that occurs between mass extinctions.

This background rate indicates how fast species would be expected to disappear in absence of human endeavour, and it’s mostly measured using the fossil record to count how many species died out between mass extinction events.

The Christmas Island Pipistrelle was announced to be extinct in 2009, years after conservationists raised concerns about its future.
Lindy Lumsden

The most accepted background rate estimated from the fossil record gives an average lifespan of about one million years for a species, or one species extinction per million species-years. But this estimated rate is highly uncertain, ranging between 0.1 and 2.0 extinctions per million species-years. Whether we are now indeed in a sixth mass extinction depends to some extent on the true value of this rate. Otherwise, it’s difficult to compare Earth’s situation today with the past.

In contrast to the the Big Five, today’s species losses are driven by a mix of direct and indirect human activities, such as the destruction and fragmentation of habitats, direct exploitation like fishing and hunting, chemical pollution, invasive species, and human-caused global warming.

If we use the same approach to estimate today’s extinctions per million species-years, we come up with a rate that is between ten and 10,000 times higher than the background rate.

Even considering a conservative background rate of two extinctions per million species-years, the number of species that have gone extinct in the last century would have otherwise taken between 800 and 10,000 years to disappear if they were merely succumbing to the expected extinctions that happen at random. This alone supports the notion that the Earth is at least experiencing many more extinctions than expected from the background rate.

An endangered Indian wild dog, or Dhole. Before extinction comes a period of dwindling numbers and spread.
from http://www.shutterstock.com

It would likely take several millions of years of normal evolutionary diversification to “restore” the Earth’s species to what they were prior to human beings rapidly changing the planet. Among land vertebrates (species with an internal skeleton), 322 species have been recorded going extinct since the year 1500, or about 1.2 species going extinction every two years.

If this doesn’t sound like much, it’s important to remember extinction is always preceded by a loss in population abundance and shrinking distributions. Based on the number of decreasing vertebrate species listed in the International Union for Conservation of Nature’s Red List of Threatened Species, 32% of all known species across all ecosystems and groups are decreasing in abundance and range. In fact, the Earth has lost about 60% of all vertebrate individuals since 1970.

Australia has one of the worst recent extinction records of any continent, with more than 100 species of vertebrates going extinct since the first people arrived over 50 thousand years ago. And more than 300 animal and 1,000 plant species are now considered threatened with imminent extinction.




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Although biologists are still debating how much the current extinction rate exceeds the background rate, even the most conservative estimates reveal an exceptionally rapid loss of biodiversity typical of a mass extinction event.

In fact, some studies show that the interacting conditions experienced today, such as accelerated climate change, changing atmospheric composition caused by human industry, and abnormal ecological stresses arising from human consumption of resources, define a perfect storm for extinctions. All these conditions together indicate that a sixth mass extinction is already well under way.




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The Conversation


Frédérik Saltré, Research Fellow in Ecology & Associate Investigator for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University and Corey J. A. Bradshaw, Matthew Flinders Fellow in Global Ecology and Models Theme Leader for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University

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

Why municipal waste-to-energy incineration is not the answer to NZ’s plastic waste crisis



Since the Chinese plastic recycling market closed, 58% of New Zealand’s plastic waste goes to countries in South-East Asia.
from http://www.shutterstock.com, CC BY-ND

Trisia Farrelly, Massey University

New Zealand is ranked the third-most-wasteful country in the OECD. New Zealanders produce five times the global daily average of waste per person – and they are getting more wasteful, producing 35% more than a decade ago.

These statistics are likely to get worse following China’s 2018 ban on imports of certain recyclable products. China was the world’s top importer of recyclable plastics, but implemented the ban because it could no longer safely manage its domestic and imported waste. Unsurprisingly, in 2015, China was named the top source of marine plastic pollution in the world.

Since the Chinese market closed, 58% of New Zealand’s plastic waste now goes to Malaysia, Indonesia, the Philippines, Thailand and Vietnam — all countries with weak regulations and high rankings as global sources of marine plastic pollution.

Waste-to-energy (WtE) incineration has been raised as a solution. While turning plastic waste into energy may sound good, it creates more pollution and delays a necessary transition to a circular economy.




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Dirty plastics

Shipments of plastic recycling often arrive in developing countries unsorted and contaminated. Materials that cannot be easily recycled are commonly burned, releasing dioxins into air, soil and water. In response, South-East Asian countries have started returning dirty plastics to developed countries.

Several New Zealand councils have stopped collecting certain plastics for recycling offshore. They are sending them to landfill instead. Available data suggest that even before the China ban plastics made up roughly 15% of the waste in municipal landfills – about 250,000 tonnes a year. Much of this is imported plastic packaging.

Many New Zealanders are very or extremely worried about the impact of plastic waste. We cannot continue ignoring our role in the global plastic pollution crisis while dumping plastic in homegrown landfills or in developing countries.




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In the scramble to find alternatives, waste-to-energy (WtE) incineration has become a hot topic, particularly as foreign investors look to establish WtE incinerators on the West Coast and [other centres]in New Zealand. Some local government representatives have endorsed WtE proposals, or raised WtE as an election issue.

Less plastic good for climate

Like landfills, WtE incinerators symbolise the linear “take-make-waste” economy, which destroys valuable resources and perpetuates waste generation.

Globally, countries are moving to circular approaches instead, which follow the “zero waste hierarchy”. This prioritises waste prevention, reduction, reuse, recycling and composting and considers WtE unacceptable.

Some New Zealanders say Nordic countries have proven that incineration is the environmental silver bullet to our waste woes. But a recent study found these countries will not meet EU circular economy goals unless they replace WtE incineration with policies that reduce waste generation. Such policies include packaging taxes, recycling and recovery rate targets, landfill bans on biodegradable waste, deposit return schemes and extended producer responsibility.

Rejecting linear approaches is also good for the climate. Actions at the top of the waste hierarchy stop more greenhouse gases than those at the bottom.

In contrast, WtE incinerators can produce 1.2 tonnes of carbon dioxide per tonne of municipal solid waste burnt. New Zealand’s zero carbon act means we have a responsibility to ensure we do not increase our greenhouse gas emissions by investing in WtE incineration.

Incinerators also cannot magic away toxins in plastic waste. Even the most high-tech WtE incinerators [[release dioxins and other pollutants into the air]. Meanwhile, toxin-laden fly ash and slag are dumped in landfills to eventually leach into the environment and contaminate food systems.

Shifting responsibility for plastic waste

To address plastic pollution, it is easy to see how prevention and reduction work better than “getting rid of” plastic once produced. Many WtE proponents argue that incineration technology can be a temporary solution for the plastic waste we have already created.

But incinerators are not short-term fixes. They are expensive to build and maintain. Large-scale incinerators demand about 100,000 tonnes of municipal solid waste a year, encouraging increasing production of waste. Investors guarantee returns on their investment by locking councils into decades-long contracts.

The only real solution to our plastics problem is through regulation that moves New Zealand towards a circular economy. We can start by making the linear economy expensive by increasing landfill levies above the current $NZ10/tonne and expanding it to all landfills. We must also invest in better waste collection, sorting and recycling systems, including a national network of resource recovery centres.

Instead of burning or burying plastic that cannot be reused, recycled or composted, we can prevent or reduce it through targeted phase-outs. The government is proposing to regulate single-use plastic packaging, beverage packaging, electronic waste and farm plastics through mandatory product stewardship schemes. This would make manufacturers responsible for the waste they produce and provide incentives for less wasteful and toxic product design and delivery systems (e.g. refill stations).

All of these circular solutions will provide far more jobs than WtE incineration.

Without a swift, brave shift to a circular economy, New Zealand will remain one of the world’s most wasteful nations. Circular economies are developing globally and WtE incineration will only set us back by 30 years.


Hannah Blumhardt, the coordinator of the NZ Product Stewardship Council, has contributed to this article.The Conversation

Trisia Farrelly, Senior Lecturer, Massey University

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