Climate explained: why higher carbon dioxide levels aren’t good news, even if some plants grow faster



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Sebastian Leuzinger, Auckland University of Technology

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz

If carbon dioxide levels were to double, how much increase in plant growth would this cause? How much of the world’s deserts would disappear due to plants’ increased drought tolerance in a high carbon dioxide environment?

Compared to pre-industrial levels, the concentration of carbon dioxide (CO₂) in the atmosphere will have doubled in about 20 to 30 years, depending on how much CO₂ we emit over the coming years. More CO₂ generally leads to higher rates of photosynthesis and less water consumption in plants.

At first sight, it seems more CO₂ can only be beneficial to plants, but things are a lot more complex than that.




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Let’s look at the first part of the question.

Some plants do grow faster under elevated levels of atmospheric CO₂, but this happens mostly in crops and young trees, and generally not in mature forests.

Even if plants grew twice as fast under doubled CO₂ levels, it would not mean they strip twice as much CO₂ from the atmosphere. Plants take carbon from the atmosphere as they grow, but that carbon is going straight back via natural decomposition when plants die or when they are harvested and consumed.

At best, you might be mowing your lawn twice as often or harvesting your plantation forests earlier.

The most important aspect is how long the carbon stays locked away from the atmosphere – and this is where we have to make a clear distinction between increased carbon flux (faster growth) or an increasing carbon pool (actual carbon sequestration). Your bank account is a useful analogy to illustrate this difference: fluxes are transfers, pools are balances.




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The global carbon budget

Of the almost 10 billion tonnes (gigatonnes, or Gt) of carbon we emit every year through the burning of fossil fuels, only about half accumulates in the atmosphere. Around a quarter ends up in the ocean (about 2.4 Gt), and the remainder (about 3 Gt) is thought to be taken up by terrestrial plants.

While the ocean and the atmospheric sinks are relatively easy to quantify, the terrestrial sink isn’t. In fact, the 3 Gt can be thought of more as an unaccounted residual. Ultimately, the emitted carbon needs to go somewhere, and if it isn’t the ocean or the atmosphere, it must be the land.

So yes, the terrestrial system takes up a substantial proportion of the carbon we emit, but the attribution of this sink to elevated levels of CO₂ is difficult. This is because many other factors may contribute to the land carbon sink: rising temperature, increased use of fertilisers and atmospheric nitrogen deposition, changed land management (including land abandonment), and changes in species composition.

Current estimates assign about a quarter of this land sink to elevated levels of CO₂, but estimates are very uncertain.

In summary, rising CO₂ leads to faster plant growth – sometimes. And this increased growth only partly contributes to sequestering carbon from the atmosphere. The important questions are how long this carbon is locked away from the atmosphere, and how much longer the currently observed land sink will continue.




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The second part of the question refers to a side-effect of rising levels of CO₂ in the air: the fact that it enables plants to save water.

Plants regulate the exchange of carbon dioxide and water vapour by opening or closing small pores, called stomata, on the surface of their leaves. Under higher concentrations of CO₂, they can reduce the opening of these pores, and that in turn means they lose less water.

This alleviates drought stress in already dry areas. But again, the issue is more complex because CO₂ is not the only parameter that changes. Dry areas also get warmer, which means that more water evaporates and this often compensates for the water-saving effect.

Overall, rising CO₂ has contributed to some degree to the greening of Earth, but it is likely that this trend will not continue under the much more complex combination of global change drivers, particularly in arid regions.The Conversation

Sebastian Leuzinger, Professor, Auckland University of Technology

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

Cutting ‘green tape’ may be good politicking, but it’s bad policy. Here are 5 examples of regulation failure



The eastern tributary in the Woronora drinking water catchment
Ian Wright, Author provided

Ian Wright, Western Sydney University

Debate about how Australia will emerge from the coronavirus pandemic is heating up. As part of the economic recovery, business groups have renewed calls to cut “green tape” – environmental regulation that new projects, such as new mines, must follow.

In response, federal environment minister Sussan Ley wants to introduce new legislation to cut green tape and speed up project approvals.




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However a major ten-yearly review of the federal government’s key environment legislation is not due to be finished until October.

Cutting green tape is a long-held aim of the Morrison government, which claims excessive environmental regulation unfairly stifles businesses.

But this isn’t the case. In my 30 years of experience researching water pollution, “green tape” has not translated into effective environmental regulation of industry. In fact, I’m yet to see a coal mining operation that’s effectively regulated after approved through the NSW and federal environmental assessment processes.

Here are five examples that show how existing environmental regulations have done little to prevent pollution and toxic chemicals from entering the environment.

1. Closed mines pollute for decades

My research on water pollution from coal mines in the Sydney basin routinely reveals inadequate environmental regulation. I’ve repeatedly uncovered long-standing environmental issues the industry doesn’t seem to learn from, such as pollution continually leaching from active and closed mines.




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As part of my PhD research in 2002/3, I studied Canyon Colliery – a coal mine deep in the Blue Mountains that closed in 1997. The mine constantly releases large volumes of toxic zinc and nickel contaminated water from the flooded underground workings into an otherwise pristine mountain stream.

This caused ecological damage in the Grose River, including a steep reduction in species and numbers of river invertebrates below the entry of the mine wastes into the river.

Contaminated drainage washing out of the closed canyon mine in Blue Mountains National Park.
Ian Wright, Author provided

It’s now 23 years since the mining stopped, but the pollution continues – testimony of weak and ineffective environmental regulation. And it will probably last for centuries.

The Canyon Mine is just one of thousands of contaminated, derelict mining and industrial sites dotted around Australia lacking environmental controls.

2. Wollangambe River

Environmental regulation has become more stringent in the last 25 years thanks to legislation introduced by the Howard government in 1999, and NSW’s Protection of the Environment Operations Act introduced in 1997.

But despite this legislation, many new and active mines that lead to environmental damage have been assessed and approved.

Research by my team at Western Sydney University has documented pollution from an active Blue Mountains coal mine, Clarence Colliery.

The mine caused severe metal contamination and ecological damage to the Wollangambe, a World Heritage River. Our research led to the NSW Environment Protection Authority (EPA) in 2017 imposing more effective restrictions on the release of toxic pollutants from the mine.

The author sampling water in the contaminated Wollangambe River.
Author provided

Despite approvals from both the NSW and federal governments, it seemed no one had noticed the magnitude of pollution from poorly treated mine wastes until our research was conducted. This caused ecological degradation to more than 20 kilometres of the highly “protected” Wollangambe River.

The Conversation contacted Centennial Coal, which owns Clarence Colliery, for comment. They directed us to their statements in 2017, when the EPA finished a five-year review of Clarence’s Environmental Protection Licence (EPL). Then, the company said:

As a result of this review Clarence will operate under a new EPL which will include agreed reductions in metal concentration limits for all water discharged to the Wollangambe. Salinity targets will also be set at 100 EC (electrical conductivity).

Clarence will also be required to comply with a Pollution Reduction Programme (PRP), also issued by the EPA, which will result in Centennial formalising options to address all water quality issues and to meet specific water quality milestones.

3. Georges River

In 2010 I made a submission as part of the environmental assessment for an extension of BHP Billiton’s Bulli Seam coal mining operations (now owned by South 32).

This involved reading thousands of pages of consultant reports explaining how the expanded operation would attempt to avoid or minimise impacts to the environment.

The mine extension was approved. Despite the many “green tape” hurdles, the approved mine was allowed to discharge wastes which our research discovered contained pollutants that were hazardous to river life in the Georges River. These included salt, nickel, zinc, aluminium and arsenic polluting the upper Georges River.

Environmental groups took the coal mine owner to court in 2012, and I provided my evidence for the court case to the NSW EPA.

The EPA has since worked with the coal miner to reduce pollution from the mine.

4. Coal mining under Sydney’s water supply

Many were stunned on March 16 this year, when the NSW government signed off on new coal mine “longwalls” directly under Woronora Reservoir, part of Sydney’s drinking water supply.

Longwall mining is the continuous mechanical removal of coal in underground mines that allows the roof of the mine to cave in after the coal is removed.

So what can they do to a river? Redbank Creek near Picton – 65 kilometres southwest of Sydney – provides a sad testimony.

Redbank Creek no longer flows normally, but has isolated pools of contaminated water.
Ian Wright, Author provided

For nearly a decade, I documented damage where falling ground levels (subsidence) caused by longwalls led to extensive damage to the creek channel.

The land surface fell more than one meter. This caused cracking, warping and buckling of the creek channel. It now rarely holds water in many stretches. Isolated stagnant pools in the creek now accumulate saline and metal-contaminated water containing little aquatic life except for mosquitoes.

The mine responsible for this damage, Tahmoor Colliery, is seeking to extend its operations and the NSW government is currently considering the development.

This mine also disposes of about four to eight megalitres of poorly treated wastes each day to the Bargo River, a popular freshwater swimming river for south-western Sydney.

5. PFAS contamination

Despite the existence of “green tape”, unforeseen problems have left Australia with many contaminated sites that may never be fully cleaned up.

We’ve seen this in the dozens of locations across Australia where toxic PFAS chemicals have contaminated land, water, ecosystems and people.




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These were previously regarded as safe chemical additives, for example in fire fighting foam, particularly at military bases.

Such contamination is very expensive to remediate and in February this year landholders near three defence bases reached a financial settlement for the PFAS damage to their property.

“Green tape” is an emotive word implying unnecessary and slow environmental regulation that delays major projects.

Given my own direct experience involved poorly regulated coal mines, I shudder to imagine the environmental degradation “fast-tracked” environmental regulation will lead to.


The Conversation also contacted SIMEC, which owns Tahmoor Colliery. A spokesperson said:

Mining in NSW is governed by stringent state and federal laws enforced by a number of government departments and regulators. SIMEC Mining acquired the Tahmoor Coking Coal Mine two years ago and takes its environmental, compliance and social responsibilities seriously.

Tahmoor Mine has been operating for well over 40 years. We acknowledge that historical mine activity did impact Redbank Creek and that this was self-reported to the regulator. Since then, SIMEC has worked closely with the NSW Department of Planning, Industry and Environment (DPIE) to enact a comprehensive plan to rehabilitate the creek. Recent rainfall has demonstrated the success of this work and we are confident that the rehabilitation works will restore the creek.

While our operations do produce water as part of the mining process, this is treated and monitored in accordance with our licence conditions. The quality of this water is mandated by our environment protection licence issued and monitored by the NSW Environmental Protection Authority (EPA). Typically, the water monitoring results are well below those limits allowed by the licence. To further improve water quality, SIMEC Mining has committed to the installation of a new water treatment plant.

Water management has been a key focus for SIMEC in the planning of the proposed Tahmoor South extension. We have commissioned extensive specialist assessments to understand any potential impact on ground and surface water. If our extension is approved, these water assets will be carefully monitored throughout the life of the mine to ensure that should any issue occur, it is detected early and resolved efficiently.The Conversation

Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University

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

Using lots of plastic packaging during the coronavirus crisis? You’re not alone


Daiane Scaraboto, University of Melbourne; Alison M Joubert, The University of Queensland, and Claudia Gonzalez-Arcos, The University of Queensland

In eight years, US environmentalist and social media star Lauren Singer had never sent an item of rubbish to landfill. But last month, in an impassioned post to her 383,000 Instagram followers, she admitted the reality of COVID-19 has changed that.

I sacrificed my values and bought items in plastic. Lots of it, and plastic that I know isn’t recyclable in NYC (New York City) recycling or maybe even anywhere … why would I go against something that I have actively prioritised and promoted?

Singer wrote that as the seriousness of COVID-19 dawned, she stocked up on items she’d need if confined to her home for a long period – much of it packaged in plastic.

Her confession encapsulates how the pandemic has challenged those of us who are trying to reduce our waste. Many sustainability-conscious people may now find themselves with cupboards stocked with plastic bottles of hand sanitiser, disposable wipes and takeaway food containers.

So let’s look at why this is happening, and what to do about it.

Sustainability out the window

We research how consumers respond to change, such as why consumers largely resisted single-use plastic bag bans. Recently we’ve explored how the coronavirus has changed the use of plastic bags, containers and other disposable products.

Amid understandable concern over health and hygiene during the pandemic, the problem of disposable plastics has taken a back seat.

For example, Coles’ home delivery service is delivering items in plastic bags (albeit reusable ones) and many coffee shops have banned reusable mugs, including global Starbucks branches.




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Restaurants and other food businesses can now only offer home delivery or takeaway options. Many won’t allow customers to bring their own containers, defaulting to disposables which generate plastic waste. This means many consumers can’t reduce their plastic waste, even if they wanted to.

Demand for products such as disposable wipes, cleaning agents, hand sanitiser, disposable gloves and masks is at a record high. Unfortunately, they’re also being thrown out in unprecedented volumes.

And the imperative to prevent the spread of coronavirus means tonnes of medical waste is being generated. For example, hospitals and aged care facilities have been advised to double-bag clinical waste from COVID-19 patients. While this is a necessary measure, it adds to the plastic waste problem.

Many cafes will not accept reusable cups during the health crisis.
The Conversation

Cause for hope

Sustainability and recycling efforts are continuing. Soft plastics recycler Red Cycle is still operating. However many dropoff points for soft plastics, such as schools and council buildings, are closed, and some supermarkets have removed their dropoff bins.

Boomerang Alliance’s Plastic Free Places program has launched a guide for cafes and restaurants during COVID-19. It shows how to avoid single-use plastics, and what compostable packaging alternatives are available.

As the guide notes, “next year the coronavirus will hopefully be a thing of the past but plastic pollution won’t be. It’s important that we don’t increase plastic waste and litter in the meantime.”

Old habits die hard

In the US, lobbyists for the plastic industry have taken advantage of health fears by arguing single-use plastic bags are a more hygienic option than reusable ones. Plastic bag bans have since been rolled back in the US and elsewhere.

However, there is little evidence to show plastic bags are a safer option, and at least reusable cloth bags can be washed.

A relaxation on plastic bag bans – even if temporary – is likely to have long-term consequences for consumer behaviour. Research shows one of the biggest challenges in promoting sustainable behaviours is to break old habits and adopt new ones. Once people return to using plastic bags, the practice becomes normalised again.

In Europe, the plastic industry is using the threat of coronavirus contamination to push back against a ban on single-use plastics such as food containers and cutlery.

Such reframing of plastic as a “protective” health material can divert attention from its dangers to the environment. Prior research, as well as our preliminary findings, suggest these meanings matter when it comes to encouraging environmentally friendly behaviours.




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Many people are using their time at home to clear out items they no longer need. However, most second-hand and charity shops are closed, so items that might have had a second life end up in landfill.

Similarly, many tool, book and toy libraries are closed, meaning some people will be buying items they might otherwise have borrowed.

Once consumers go back to using plastic bags, it will take time to break the habit again.
Darren England/AAP

What to do

We can expect the environmental cause will return to the foreground when the COVID-19 crisis has passed. In the meantime, reuse what you have, and try to store rather than throw out items for donation or recycling.

Talk to takeaway food outlets about options for using your own containers, and refuse disposable cutlery or napkins with deliveries. Use the time to upskill your coffee-making at home rather than buying it in a takeaway cup. And look for grocery suppliers offering more sustainable delivery packaging, such as cardboard boxes or biodegradable bags.

Above all, be vigilant about ways environmental protections such as plastic bag bans might be undermined during the pandemic, and voice your concerns to politicians.




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The Conversation


Daiane Scaraboto, Associate Professor of Marketing, University of Melbourne; Alison M Joubert, Lecturer in Marketing, The University of Queensland, and Claudia Gonzalez-Arcos, Lecturer in Marketing, The University of Queensland

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