Why New Zealand should not explore for more natural gas reserves

The New Zealand government is introducing legislation to become zero-carbon by 2050, but will consider new permits for coal mining, offshore oil drilling and fracking on a case-by-case basis.
from shutter stock.com, CC BY-ND

Ralph Sims, Massey University

New Zealand’s new coalition government has committed to introducing zero-carbon legislation that would set the country on a course to be carbon neutral by 2050.

At the same time, it is not ruling out new permits for coal mining, offshore oil drilling and fracking during a transition away from fossil fuels.

Natural gas is often touted as a “bridging fuel” to cut the use of coal for heat and power while moving towards a low-carbon economy. Also, this week’s report by the crown research institute Scion shows that New Zealand could build a renewable low-carbon transport fuels industry by switching to biofuels instead of natural gas. Developing new gas resources in New Zealand is a shortsighted strategy that could lead to stranded assets.

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2050 climate targets: nations are playing the long game in fighting global warming

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Carbon budget

Carbon dioxide (CO₂) is a long-lived greenhouse gas. Each molecule released into the atmosphere from burning fossil fuels remains there for hundreds of years. Analysis by the Intergovernmental Panel on Climate Change shows that once we reach a total of 2,900 billion tonnes of carbon dioxide (Gt CO₂) in the atmosphere, the planet will likely exceed the internationally agreed target to keep warming below two degrees above pre-industrial levels.

More than 1,900 Gt CO₂ have already been emitted since the late 19th century. We are currently adding around 33 Gt CO₂ from fossil fuel combustion and 5 Gt CO₂ from deforestation every year. The atmospheric concentration of CO₂ has now surged to more than 403 parts per million, the highest in millions of years. The planet is already around one degree warmer than the average pre-industrial temperature.

This graphic shows that we have already used up around two-thirds of the total carbon budget to avoid exceeding a two-degree average temperature rise (with a 66% chance).
IPCC, Working Group 1, 2013, CC BY-ND

The remaining carbon budget, with a 66% chance of staying below the two-degree target, is now at about 800 Gt CO₂. At the current business-as-usual rate of fossil fuel combustion and deforestation, the total budget will be exceeded within 20 to 25 years.

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By then, we will have used up around two-fifths of the known global reserves of coal, oil and natural gas. The remaining three-fifths will need to stay in the ground.

Gas as a transition fuel

Natural gas is described as a “transition fuel” that cuts the use of coal. This argument, and the case for providing greater energy security, is being used to justify exploration for deep sea oil and gas in New Zealand waters.

Displacing coal by burning conventional natural gas does indeed produce lower emissions, while providing the same heat or electricity services. A coal-fired power station produces around 900-1100 g CO₂/kWh generated; a gas-fired plant produces around 450-500 g CO₂/kWh. By way of comparison, a geothermal plant varies with the field but can emit up to 50 g CO₂/kWh and emissions from other renewable energy plants vary widely with the circumstances but tend to be much lower.

However, on a life-cycle basis, any carbon dioxide reduction benefits would be partially negated by leakage of methane (CH₄), the main component of natural gas. Leakage is inevitable during the extraction, distribution and use of natural gas. It is difficult to determine the level of leakage, but it is more certain that emissions from coal or gas plants are significantly higher than from a renewable energy plant of similar generation output.

Natural gas has the potential to extend the time before the carbon budget is used up, assuming it displaces coal that would then be left in the ground. But the use of gas cannot deliver the deep cuts in emissions that will be required to stay below two degrees.

Energy security and fossil fuel subsidies

Many nations, including New Zealand, aim to improve their energy security by shifting to more indigenous fossil fuel resources to reduce their dependence on imports and widely fluctuating prices. Exploring for more gas to meet local demands at contracted prices may make good political sense in the short term, but it exacerbates climate change.

Fossil fuel exploration, production and consumption is widely subsidised by many governments. The International Energy Agency estimated the value of consumer subsidies in 2016 was over US$260 billion.

Conversely, divestment away from fossil fuel companies is growing worldwide. For example, New York City is not only intending to divest US$5 billion of its holdings in fossil fuel assets, but also plans to sue the major oil companies over their contribution to climate change.

New Zealand’s economy without more gas

In New Zealand, natural gas is used to generate electricity and heat for industries, to produce methanol (mainly for export) and other petrochemical products such as urea. It also supplies around 277,000 domestic and commercial consumers in the North Island.

Currently around 1,200,000 tonnes per year (t/yr) of coal are consumed in New Zealand, mainly for heat and electricity, emitting around 2.6 Mt CO₂/yr. If all existing coal plants and heating systems were converted to gas, around 1.3 Mt CO₂/yr of emissions would be avoided. This would contribute a little towards the 20 Mt CO₂-eq/yr of emissions reductions needed to meet New Zealand’s current 2030 target under the Paris Agreement.

However, given the Government’s target to reach net-zero emissions by mid-century, gas will ultimately need to be entirely phased out together with coal and oil products. Therefore, the overall aims for New Zealand should be to:

• use our existing reserves of natural gas wisely in order to gain maximum long-term economic benefits by maximising the return on investments already made, as well as reducing our annual CO₂ emissions by displacing coal and minimising methane leakage

• invest significantly in research and development in sustainable energy, including low-carbon and economically viable alternatives for the current uses of existing gas supplies

• clarify and quantify any fossil fuel producer and consumer subsidies and remove them in the near future

• avoid the temptation to explore and develop new gas resources even if they appear to deliver short-term economic benefits; and

• invest in renewable energy technologies, including biofuels, as long as they are produced from crop and forest residues and purpose-grown forests on marginal land, as identified in the Scion report.

Ralph Sims, Professor, School of Engineering and Advanced Technology, Massey University

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

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FactFile: the facts on shark bites and shark numbers

The CSIRO has provided new estimates of population sizes for White Sharks in Australian waters.
Fiona Ayerst/Shutterstock

Jane Williamson, Macquarie University and Vincent Raoult, University of Newcastle

Are there more sharks in Australian waters than there used to be, and are interactions between humans and shark increasing? Some Australian politicians have claimed that to be the case.

Let’s look at the research.

The most reputable source for shark incident data in Australia is the Australian Shark Attack file, which is collated at Sydney’s Taronga Zoo.

The map below, created by The Conversation using data from the Australian Shark Attack File, shows incidents between sharks and humans in Australia between 1997 and 2017.

You can use the filter buttons in the map to explore the data by year, season, the type of injury, the type of shark involved, the type of incident – or a combination of all the filters. Press the ‘show all’ button to reset the search.

https://cdn.theconversation.com/infographics/243/f87e27e72eb6545d5422e204b9894dedaad0f92f/site/index.html

The number of recorded encounters between sharks and humans in Australia increased modestly between 1997 and 2017, but the reason for this is unclear. Over those two decades, the Australian population increased by 33%, but that alone doesn’t explain the increase in recorded shark encounters.

Correcting for the growth in human population in Australia, the data show that between 1997 and 2017:

• incidents resulting in injury increased by 1.59%
• incidents without injury increased by 0.36%, and
• fatalities increased by 0.07%.

Encounters between humans and sharks are extremely variable over time, and difficult to predict. The increases in recorded incidents between 1997 and 2017 are relatively small, and may be explained by factors not related to shark populations – such as increases in the reporting of shark encounters, or increasing beach use.

https://cdn.theconversation.com/infographics/159/62c30e6dedecffbbeb4e059c8ab0e573d756f61b/site/index.html

Are there more sharks off the Australian coast?

White Sharks (formerly Great White Sharks) are recorded as being responsible for 28 of the 36 fatal shark encounters in Australian waters between 1997 and 2017, and are the primary target of shark mitigation strategies of the Western Australian, New South Wales and Queensland governments.

So, has there been an increase in the number of White Sharks in Australian waters?

Estimating population numbers in the marine environment is difficult, especially for long-lived migratory species like White Sharks.

However, there is no evidence that White Sharks numbers are on the rise, either in Western Australia or along the Eastern coast. Despite targeted conservation efforts, the available research show stable or slightly declining numbers in these populations.

There are two distinct populations of White Sharks off Australian coasts – one to the west, and another to the east of Bass Strait, which separates Tasmania from mainland Australia. The eastern population includes New Zealand White Sharks.

Recent work by the CSIRO through the National Environmental Science Program’s Marine Biodiversity Hub using innovative DNA analysis has provided us with the most detailed and reliable estimates of population size we have for this species.

The CSIRO study shows there has been a slight decline in adult White Shark populations since the year 2000.

Current adult abundance for the eastern Australasian population is estimated at 750, with an uncertainty range of 470 to 1,030. The southern-western adult population is roughly double the size, estimated at 1,460, with an uncertainty range of 760 to 2,250.

Including the available information about juvenile White Sharks, estimates of total size for the eastern population in 2017 was 5,460, with an uncertainty range of 2,909 to 12,802.

It’s difficult to detect population trends with White Sharks because of the length of time it takes juveniles to reach maturity – around 15 years. As protection of White Sharks began in the late 1990s, any changes in abundance would only be starting to appear in current populations.

How else can we measure White Shark populations?

The traditional way of measuring shark and fish populations is by examining catches in commercial fisheries over long time periods. By correcting for the level of fishing effort – which is done by looking at things like the number of nets, hooks and tows deployed by fishermen – scientists can assume that changes in the “catchability” of sharks is related to their abundance.

But due to the relative rarity of catches of White Sharks by fishing vessels, this approach is less reliable for this species than the more recent genetic studies conducted by the CSIRO and outlined above.

Western Australia has a detailed measure of White Shark numbers assessed by catch data. A report published by the Western Australian Department of Fisheries in 2016 attempted to model changes in the southern-western Australian White Shark population since the late 1930s. The authors outlined four different plausible scenarios, none of which suggested a continuous increase in the number of White Sharks.

In New South Wales, there has been a cluster of shark bites in recent years. Data from the NSW Shark Meshing (Bather Protection) Program, managed by the NSW Department of Primary Industries, show a recent increase in White Sharks caught in nets placed near ocean beaches.

But when it comes to thinking about shark populations, we should not assume that these two facts are related. It’s important to remember that just because two things may correlate, it doesn’t mean that one caused the other.

These patterns could mean that the animals are coming closer to shore, rather than a population increase (or decrease).

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Shark and human interactions: what factors are at play?

A 2016 paper examined six global shark bite “hotspots” – the United States, South Africa, Australia, Brazil, Reunion Island and the Bahamas – and concluded that when it comes to encounters between sharks and humans, there are a range of causes at play.

These include:

• rises in human population
• habitat destruction/modification
• changes in water quality
• climate change
• changing weather patterns, and
• the distribution/abundance of prey.

The authors also noted that shark encounters appear to happen in clusters. For example, 2009 saw a spike in shark encounters off the New South Wales coast. This coincided with an increase in beach attendance and beach rescues during what was an unusually warm summer for south-east Australia.

A 2011 paper highlighted the popularity of water sports as a factor contributing to increased human-shark encounters. More people are taking part in water sports, and improvements in wetsuit technology mean that people are in the water for longer throughout the year.

However, there is limited information on the number of people who use Australian beaches, so this explanation needs to be further studied.

It’s vital that any strategies put in place to reduce the number of unprovoked encounters between humans and sharks in Australian waters are carefully considered, and based on the best available research.

Jane Williamson, Associate Professor in Marine Ecology, Macquarie University and Vincent Raoult, Postdoctoral fellow, University of Newcastle

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

Australia: NSW – Sydney

Hawaii

Australia’s Emissions Reduction Fund is almost empty. It shouldn’t be refilled

Ian A. MacKenzie, The University of Queensland

Australia’s flagship climate policy, the Emissions Reduction Fund (ERF), has come in for fresh questions over whether the emissions allowances offered to big businesses will wipe out much of the progress made elsewhere.

This voluntary scheme – the central plank of Australia’s efforts to reduce greenhouse gas emissions by 26-28% below 2005 levels by 2030 – allows interested parties to reduce pollution in exchange for a proportion of the A$2.55 billion fund.

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So far, through successive rounds of “reverse auctions”, the scheme has secured 191.7 million tonnes of emission reductions, at a price tag of A$2.28 billion.

As the budget for this scheme is nearly exhausted, it is important to ask whether it has been a success, or whether Australia’s carbon policy needs a radical rethink. Overall, the answer seems to be the latter.

Safeguards not so safe

Much of the problem stems from the ERF’s safeguard mechanism, which puts limits on the greenhouse emissions from around 140 large polluting businesses. Under the mechanism, these firms are not allowed to pollute more than an agreed “baseline”, calculated on the basis of their existing operations.

The mechanism is described as a safeguard because it aims to stop big businesses wiping out the emissions reductions delivered by projects funded by the ERF. But it doesn’t appear to be working.

The government has already increased the emission baselines for many of these businesses, for arguably specious reasons. Some firms have been given extra leeway to pollute simply because their business has grown, or even just because they blew their original baseline.

Worryingly, on February 21, 2018 the federal government released a consultation document which favours “updating baselines to bring them in line with current circumstances” and suggests that “to help prevent baselines becoming out-of-date in the future, they could be updated for production more often, for example, each year”.

It doesn’t take a genius to realise that if baselines are continually increased over time, the fixed benefits of the ERF will inevitably be wiped out.

This underlines the importance of having a climate policy that operates throughout the economy, rather than only in certain parts of it. If heavily polluting businesses can so readily be allowed to undo the work of others, this is a recipe for disaster.

Contract problems

Even within the ERF process itself, many emissions reduction contracts have already been revoked. This is worrying but also avoidable if the contracts are written correctly.

It is important to note that these contracts run for around seven years, and thus it is possible that the planned carbon reductions never eventuate. Currently only about 16% of the announced 191.7 million tonnes of emissions reduction have actually been delivered.

For the ERF to work effectively, the government needs to know the “counterfactual” emissions – that is, firms’ emissions if they decided not to participate in the ERF. Yet this is completely unknown.

This means that projects that successfully bid for ERF funding (typically the cheapest ones) may not be “additional”. In other words, they may have established these emissions reduction projects anyway, with or without funding from the taxpayer.

Another problem with the ERF is that it is skewed towards projects from lower-polluting sectors of the economy, whereas heavily polluting industries are underrepresented. The largest proportion of signed contracts have involved planting trees or reducing emissions from savannah burning.

Meanwhile, the firms covered by the safeguard mechanism are largely absent from the ERF itself, despite these firms accounting for around 50% of Australia’s greenhouse emissions.

The bare fact is that Australia’s flagship climate policy doesn’t target the prominent polluters.

A different way

Australia’s climate policy has had a colourful past. Yet the economics of pollution mitigation remain the same.

If we want to reduce pollution in a cost-effective way that actually works, then we must (re-)establish a carbon price.

This would provide the much-needed certainty about the cost of genuine pollution reduction. This in turn would allow all major polluters to make strategic, long-term investments that will progressively reduce emissions.

Instead of spending A$2.55 billion to pay for modest emissions reductions that might be cancelled out elsewhere, creating a carbon price will allow for the generation of tax revenue that can be used for a host of purposes.

For example, distortionary tax rates (such as income and corporation tax) could be lowered, or the revenue could be used to fund better schools and hospitals.

A clear example of such a success can be taken from the northeastern states of the US. The Regional Greenhouse Gas Initiative is a cap-and-trade market that sells tradeable pollution permits to electricity companies. Estimates have shown that US$2.3 billion of lifetime energy bill savings will occur due to investments made in 2015.

To tax or cap?

If the ERF is to be replaced, what type of carbon price do we want? Do we want a carbon tax or a cap-and-trade market?

While advantages exist for both, most evidence shows that carbon taxes are more efficient at driving down emissions. Moreover, taxation avoids the potential problems of market power, which may exist with a small number of large polluters.

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A carbon price would also remove much of the political rent-seeking that is encouraged by Australia’s current policy settings. A simple, economy-wide carbon tax would be more transparent than the safeguard mechanism, under which individual firms can plead for leniency.

With the ERF fund almost empty, the federal government should ask itself a tough question. Should it spend another A$2.55 billion of taxpayers’ money while letting major polluters increase their emissions? Or should it embrace a new source of tax revenue that incentivises cleaner technologies in a transparent, cost-effective way?

Ian A. MacKenzie, Senior Lecturer in Economics, The University of Queensland

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

Our acid oceans will dissolve coral reef sands within decades

Researchers studied reef sands at Heron Island, Hawaii, Bermuda and Tetiaroa. In this photo, white areas show the predominance of sand on reefs.
Southern Cross University

Bradley Eyre, Southern Cross University

Carbonate sands on coral reefs will start dissolving within about 30 years, on average, as oceans become more acidic, new research published today in Science shows.

Carbonate sands, which accumulate over thousands of years from the breakdown of coral and other reef organisms, are the building material for the frameworks of coral reefs and shallow reef environments like lagoons, reef flats and coral sand cays.

But these sands are sensitive to the chemical make-up of sea water. As oceans absorb carbon dioxide, they acidify – and at a certain point, carbonate sands simply start to dissolve.

The world’s oceans have absorbed around one-third of human-emitted carbon dioxide.

Carbonate sand is vulnerable

For a coral reef to grow or be maintained, the rate of carbonate production (plus any external sediment supply) must be greater than the loss through physical, chemical and biological erosion, transport and dissolution.

It is well known that ocean acidification reduces the amount of carbonate material produced by corals. Our work shows that reefs face a double-whammy: the amount of carbonate material produced will decrease, and the newly produced and stored carbonate sands will also dissolve.

Researchers used benthic chambers (pictured) to test how different levels of seawater acidity affect reef sediments.
Steve Dalton/Southern Cross University

We measured the impact of acidity on carbonate sands by placing underwater chambers over coral reefs sands at Heron Island, Hawaii, Bermuda and Tetiaroa in the Pacific and Atlantic Oceans. Some of the chambers were then acidified to represent future ocean conditions.

The rate at which the sands dissolve was strongly related to the acidity of the overlying seawater, and was ten times more sensitive than coral growth to ocean acidification. In other words, ocean acidification will impact the dissolution of coral reef sands more than the growth of corals.

This probably reflects the corals’ ability to modify their environment and partially adjust to ocean acidification, whereas the dissolution of sands is a geochemical process that cannot adapt.

Sands on all four reefs showed the same response to future ocean acidification, but the impact of ocean acidification on each reef is different due to different starting conditions. Carbonate sands in Hawaii are already dissolving due to ocean acidification, because this coral reef site is already disturbed by pollution from nutrients and organic matter from the land. The input of nutrients stimulates algal growth on the reef.

In contrast, carbonate sands in Tetiaroa are not dissolving under current ocean acidification because this site is almost pristine.

What will this mean for coral reefs?

Our modelling at 22 locations shows that net sand dissolution will vary for each reef. However, by the end of the century all but two reefs across the three ocean basins would on average experience net dissolution of the sands.

A transition to net sand dissolution will result in loss of material for building shallow reef habitats such as reef flats and lagoons and associated coral cays. What we don’t know is whether an entire reef will slowly erode or simply collapse, once the sediments become net dissolving, as the corals will still grow and create reef framework. Although they will most likely just slowly erode.

It may be possible to reduce the impact of ocean acidification on the dissolution of reef sands, by managing the impact of organic matter like algae at local and regional scales. This may provide some hope for some already disturbed reefs, but much more research on this topic is required.

Ultimately, the only way we can stop the oceans acidifying and the dissolving of coral reefs is concerted action to lower CO₂ emissions.

Bradley Eyre, Professor of Biogeochemistry, Director of the Centre for Coastal Biogeochemistry, Southern Cross University

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

Should Australia recognise the human right to a healthy environment?

Australia is one of very few countries that does not recognise the right to a healthy environment.
Jordan Davis, Author provided

Meg Good, University of Tasmania

Australia is one of only 15 nations (a list that also includes Canada and the United States) that does not recognise the human right to a healthy environment at the federal level.

Last year, the Australian Panel of Experts on Environmental Law recommended that environmental democracy in Australia “must have as a foundation, respect for fundamental human rights and, in particular, an enforceable right to a clean and healthy environment”.

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Suggestions have also been made by various academics and environmental protection organisations to recognise the right in existing and proposed state human rights charters, including the soon-to-be-developed Queensland Human Rights Act.

So should Australia heed these calls and recognise the right? The global experience with environmental rights recognition suggests that it could be beneficial.

Environmental protection

In 2012, Canadian environmental lawyer David Boyd published The Environmental Rights Revolution, an analysis of the dozens of nations which have already recognised the human right to a healthy environment in their constitutions.

Although there is no internationally accepted definition of the right, Boyd cites the Stockholm Declaration as its first formal recognition:

Man has the fundamental right to freedom, equality and adequate conditions of life, in an environment of a quality that permits a life of dignity and well-being, and he bears a solemn responsibility to protect and improve the environment for present and future generations.

His research found that across Latin America, Europe and Asia, the right to a healthy environment has helped to strengthen existing environmental protection laws and policies and encouraged the introduction of new stronger legislation. Significantly, it has also prevented governments from “rolling back” effective laws created by their predecessors.

Lawsuits utilising the right have been successful in achieving better protection for the environment, safeguarding crucial natural resources for current and future generations.

Whether Australia would enjoy similar benefits would significantly depend on the expression of the right and the form of legal recognition adopted.

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The government vs the environment: lawfare in Australia

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In Latvia, the right is expressed as a right to live in a “benevolent environment”, whereas in Brazil citizens are granted a right to an “ecologically balanced environment”. Exactly how the right would be expressed in Australia would be a question for parliament.

It’s highly unlikely the Australian Constitution would be changed to incorporate the right (since 1906, constitutional reform has succeeded only eight times), so it’s probable that Australia would recognise the right through legislation.

Although Australia has so far resisted introducing comprehensive national human rights legislation, the right could be recognised within a statutory bill of human rights based on the “dialogue model”.

The dialogue model of recognition

Recommended by the National Human Rights Consultation Committee, the dialogue model involves all three arms of government engaging in a “dialogue” about human rights protection. It requires public authorities to act in line with protected rights, and courts to (if possible) interpret legislation in a compatible manner.

However, one of the most powerful consequences of recognising the right within this model is that all future legislation would be scrutinised for consistency with the right.

Australia already has a Parliamentary Joint Committee on Human Rights, which examines the compatibility of proposed legislation with specified international human rights standards. Presumably, if the right was recognised in a federal bill of rights, the Committee’s mandate would alter to include consideration of all rights recognised under the legislation.

At present, the Committee is not required to consider the compatibility of proposed legislation with the human right to a healthy environment.

This was highlighted in 2016, when the federal government controversially proposed amending the nation’s key environmental protection legislation to limit standing for environmental protection groups to challenge decisions made under the Act.

Due to the Minister stating that there is “no standalone right to a healthy environment”, the Committee only considered the legislation’s impact on environmental protection indirectly through consideration of its impact on the right to health (which includes the “underlying determinants of health”, such as a healthy environment).

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Ideally, the Committee would be empowered to consider the impacts of proposed legislation on the right to a healthy environment directly. This scrutiny process would help to ensure that proposals which jeopardise the government’s ability to protect, respect and fulfil the right could be identified and challenged before they pass into law.

A limited but useful tool

Under the dialogue model, the parliament retains the final say, meaning it would still be possible for the legislature to pass legislation manifestly incompatible with the right. The “safety net” of protection offered by this form of recognition would not suffice to address all potential and actual breaches of the right, or even guarantee its fulfilment.

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However, it would ensure that the right enters the legal and policy discourse around natural resources management and sustainable development.

In a time of unprecedented climate change, the right invites another way of thinking about our relationship with the natural world, and offers a useful tool for improving environmental protection in Australia.

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This article is based on the author’s 2016 PhD thesis which proposed legal recognition of the human right to a healthy environment in Australia under a statutory bill of rights.

Meg Good, Adjunct Lecturer, Faculty of Law, University of Tasmania

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

Light Pollution and Night Skies

I’ve always wondered: why many people in Asian countries wear masks, and whether they work

Face masks are a common sight in Asia. Why?
David Chang/AAP

C Raina MacIntyre, UNSW and Abrar Ahmad Chughtai, UNSW

This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au

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In Japan, many people wear face masks – is that to prevent the wearer getting the infection, or is the wearer already infected and protecting those around? Is the mask useful in protecting against viruses or bacteria? – Petrina, Greenwich

Thanks for your question, Petrina. You’re right, in countries like Japan and China, facemask use in the community is widespread – much more so than in Western cultures. People wear them to protect the respiratory tract from pollution and infection, and to prevent the spread of any pathogens they might be carrying.

Whether this works depends on the type of mask.

There are three supposed ways a mask can provide protection: by providing a physical barrier (which prevents splashes and sprays), by filtering the particles (blocking particles of a certain size from entering the respiratory tract), and by fitting around the face to prevent leakage of air around the sides.

Some mask makers have also gone the extra step of using antimicrobials and claim to kill bugs on the surface of the mask, but these haven’t been tested to see if they provide any benefit.

Healthcare workers have been using cloth masks (made of cotton or other materials and with ties to secure them at the back) while caring for patients since the late 19th century to protect from various respiratory infections such as diphtheria, scarlet fever, measles, pandemic influenza, pneumonic plague and tuberculosis.

Cloth masks have been around since the late 19th century.
Author provided

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During the mid 20th century, disposable surgical facemasks (similar in look to the cloth masks but made of paper) were developed. Surgical masks were developed to prevent the surgeon from contaminating the wound during surgery, but studies have not proven they help.

Surgical masks have no evidence of effectiveness.
from http://www.shutterstock.com

These were followed by respirators, which vary in shape and material but are designed to fit around the face and filter particles. Respirators are designed specifically to protect the respiratory tract from inhaled germs. There are many types, which may be reusable or disposable.

People must undergo fit-testing to ensure respirators are correctly fitted, with a good seal around the face. Unlike masks, respirators are subject to certification and regulation, and are proven to protect against respiratory infection.

Respirators are proven to protect against infection.
from http://www.shutterstock.com

Surgical masks are unregulated for filtration and do not fit around the face, and the evidence for their use is less convincing. In a community study, families with a sick child who wore such a mask were less likely to get sick if they also wore a mask, but many family members didn’t wear their masks all the time.

In a university setting, students were protected from sick classmates if they wore the mask within 36 hours of their classmate getting sick.

In many low income countries, the cost of even paper surgical masks is prohibitive, so cloth masks are used, washed and re-used. But these don’t protect against infection, and may even increase the risk of infection.

Prevention of infection vs source control

Masks can be used to protect healthy people (such as nurses and doctors) from exposure to infection, but are also used by sick people (such as a TB patient) to prevent spread of infections to others (called “source control”). There is less research on this use than on the use of masks by well people. The efficacy of source control is unknown.

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Do masks work?

It’s long been thought surgical masks protect from transmission of pathogens, which spread through the air on large, short-range droplets, while respirators protect against much smaller, airborne particles, which may remain suspended in the air for several hours and transmit infection over long distances. So most guidelines recommend a mask for droplet transmitting infections (such as influenza) and a respirator for airborne infections (such as TB and measles).

But we’ve shown respirators protect better than masks even against droplet-spread infections. And the longstanding belief that infections neatly fit into either droplet or airborne transmission is not correct. Respiratory transmission of infections is more complex than this.

To say whether masks work, we have to specify whether we’re talking about a respirator, a surgical mask or a cloth mask.

The respirators are the Rolls Royce option and do protect, and this is a tool for frontline health workers facing epidemics of known and unknown infections. Surgical masks probably also protect but to a lesser extent. But there’s no evidence cloth masks will protect against invading or escaping bugs.

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C Raina MacIntyre, Professor of Infectious Diseases Epidemiology, Head of the School of Public Health and Community Medicine, UNSW and Abrar Ahmad Chughtai, Epidemiologist, UNSW

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

Perseid Meteor Shower