Rising carbon dioxide is making the world’s plants more water-wise


Pep Canadell, CSIRO; Francis Chiew, CSIRO; Lei Cheng, CSIRO; Lu Zhang, CSIRO, and Yingping Wang, CSIRO

Land plants are absorbing 17% more carbon dioxide from the atmosphere now than 30 years ago, our research published today shows. Equally extraordinarily, our study also shows that the vegetation is hardly using any extra water to do it, suggesting that global change is causing the world’s plants to grow in a more water-efficient way.

Water is the most precious resource needed for plants to grow, and our research suggests that vegetation is becoming much better at using it in a world in which CO₂ levels continue to rise.

The ratio of carbon uptake to water loss by ecosystems is what we call “water use efficiency”, and it is one of the most important variables when studying these ecosystems.

Our confirmation of a global trend of increasing water use efficiency is a rare piece of good news when it comes to the consequences of global environmental change. It will strengthen plants’ vital role as global carbon sinks, improve food production, and might boost water availability for the well-being of society and the natural world.

Yet more efficient water use by the world’s plants will not solve our current or future water scarcity problems.

Changes in global terrestrial uptake of carbon dioxide, water use efficiency and ecosystem evapotranspiration during 1982-2011.

Boosting carbon uptake

Plants growing in today’s higher-CO₂ conditions can take up more carbon – the so-called CO₂ fertilisation effect. This is the main reason why the terrestrial biosphere has taken up 17% more carbon over the past 30 years.

The enhanced carbon uptake is consistent with the global greening trend observed by satellites, and the growing global land carbon sink which removes about one-third of all CO₂ emissions generated by human activities.

Increasing carbon uptake typically comes at a cost. To let CO₂ in, plants have to open up pores called stomata in their leaves, which in turn allows water to sneak out. Plants thus need to strike a balance between taking up carbon to build new leaves, stems and roots, while minimising water loss in the process. This has led to sophisticated adaptations that has allowed many plant species to conquer a range of arid environments.

One such adaptation is to close the stomata slightly to allow CO₂ to enter with less water getting out. Under increasing atmospheric CO₂, the overall result is that CO₂ uptake increases while water consumption does not. This is exactly what we have found on a global scale in our new study. In fact, we found that rising CO₂ levels are causing the world’s plants to become more water-wise, almost everywhere, whether in dry places or wet ones.

Growth hotspots

We used a combination of plot-scale water flux and atmospheric measurements, and satellite observations of leaf properties, to develop and test a new water use efficiency model. The model enables us to scale up from leaf water use efficiency anywhere in the world to the entire globe.

We found that across the globe, boreal and tropical forests are particularly good at increasing ecosystem water use efficiency and uptake of CO₂. That is due in large part to the CO₂ fertilisation effect and the increase in the total amount of leaf surface area.

Importantly, both types of forests are critical in limiting the rise in atmospheric CO₂ levels. Intact tropical forest removes more atmospheric CO₂ than any other type of forest, and the boreal forests of the planet’s far north hold vast amounts of carbon particularly in their organic soils.

Meanwhile, for the semi-arid ecosystems of the world, increased water savings are a big deal. We found that Australian ecosystems, for example, are increasing their carbon uptake, especially in the northern savannas. This trend may not have been possible without an increase in ecosystem water use efficiency.

Previous studies have also shown how increased water efficiency is greening semi-arid regions and may have contributed to an increase in carbon capture in semi-arid ecosystems in Australia, Africa and South America.

Trends in water use efficiency over 1982-2011.
CREDIT, Author provided

It’s not all good news

These trends will have largely positive outcomes for the plants and the animals (and humans) consuming them. Wood production, bioenergy and crop growth are (and will be) less water-intensive under climate change than they would be without increased vegetation water use efficiency.

But despite these trends, water scarcity will nevertheless continue to constrain carbon sinks, food production and socioeconomic development.

Some studies have suggested that the water savings could also lead to increased runoff and therefore excess water availability. For dry Australia, however, more than half (64%) of the rainfall returning to the atmosphere does not go through vegetation, but through direct soil evaporation. This reduces the potential benefit from increased vegetation water use efficiency and the possibility for more water flowing to rivers and reservoirs. In fact, a recent study shows that while semi-arid regions in Australia are greening, they are also consuming more water, causing river flows to fall by 24-28%.

The ConversationOur research confirms that plants all over the world are likely to benefit from these increased water savings. However, the question of whether this will translate to more water availability for conservation or for human consumption is much less clear, and will probably vary widely from region to region.

Pep Canadell, CSIRO Scientist, and Executive Director of the Global Carbon Project, CSIRO; Francis Chiew, Senior Principal Research Scientist, CSIRO; Lei Cheng, Postdoctoral research fellow, CSIRO; Lu Zhang, Senior Principal Research Scientist, CSIRO, and Yingping Wang, Chief research scientist, CSIRO

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

Australia’s new marine parks plan is a case of the Emperor’s new clothes



File 20170724 28505 1oghl27
Orca family group at the Bremer Canyon off WA’s south coast.
R. Wellard, Author provided

Jessica Meeuwig, University of Western Australia and David Booth, University of Technology Sydney

The federal government’s new draft marine park plans are based on an unsubstantiated premise: that protection of Australia’s ocean wildlife is consistent with activities such as fishing and oil and gas exploration.

Under the proposed plans, there would be no change to the boundaries of existing marine parks, which cover 36% of Commonwealth waters, or almost 2.4 million square kilometres. But many areas inside these boundaries will be rezoned to allow for a range of activities besides conservation.

The plans propose dividing marine parks into three types of zones:

  • Green: “National Park Zones” with full conservation protection
  • Yellow: “Habitat Protection Zones” where fishing is allowed as long as the seafloor is not harmed
  • Blue: “Special Purpose Zones” that allow for specific commercial activities.

Crucially, under the new draft plans, the amount of green zones will be almost halved, from 36% to 20% of the marine park network, whereas yellow zones will almost double from 24% to 43%, compared with when the marine parks were established in 2012.

The government has said that this approach will “allow sustainable activities like commercial fishing while protecting key conservation features”.

But like the courtiers told to admire the Emperor’s non-existent new clothes, we’re being asked to believe something to be true despite strong evidence to the contrary.

The Emperor’s unrobing

The new plans follow on from last year’s release of an independent review, commissioned by the Abbott government after suspending the previous network of marine reserves implemented under Julia Gillard in 2012.

Yet the latest draft plans, which propose to gut the network of green zones, ignore many of the recommendations made in the review, which was itself an erosion of the suspended 2012 plans.

The extent of green zones is crucial, because the science says they are the engine room of conservation. Fully protected marine national parks – with no fishing, no mining, and no oil and gas drilling – deliver far more benefits to biodiversity than other zone types.

The best estimates suggest that 30-40% of the seascape should ideally be fully protected, rather than the 20% proposed under the new plans.

Partially protected areas, such as the yellow zones that allow fishing while protecting the seabed, do not generate conservation benefits equivalent to those of full protection.

While some studies suggest that partial protection is better than nothing, others suggest that these zones offer little to no improvement relative to areas fully open to exploitation.

Environment minister Josh Frydenberg has pointed out that, under the new plans, the total area zoned as either green or yellow will rise from 60% to 63% compared with the 2012 network. But yellow is not the new green. What’s more, yellow zones have similar management costs to green zones, which means that the government is proposing to spend the same amount of money for far inferior protection. And as any decent sex-ed teacher will tell you, partial protection is a risky business.

What do the draft plans mean?

Let’s take a couple of examples, starting with the Coral Sea Marine Park. This is perhaps the most disappointing rollback in the new draft plan. The green zone, which would have been one of the largest fully protected areas on the planet, has been reduced by half to allow for fishing activity in a significantly expanded yellow zone.

Coral Sea Marine Park zoning, as recommended by Independent Review (left) and in the new draft plan (right), showing the proposed expansion of partial protection (yellow) vs full protection (green).
From http://www.environment.gov.au/marinereservesreview/reports and https://parksaustralia.gov.au/marine/management/draft-plans/

This yellow zone would allow the use of pelagic longlines to fish for tuna. This is despite government statistics showing that around 30% of the catch in the Eastern Tuna and Billfish fishery consists of species that are either overexploited or uncertain in their sustainability, and the government’s own risk assessment that found these types of fishing lines are incompatible with conservation.

What this means, in effect, is that the plans to establish a world-class marine park in the Coral Sea will be significantly undermined for the sake of saving commercial tuna fishers A$4.1 million per year, or 0.3% of the total revenue from Australia’s wild-catch fisheries.

Contrast this with the A$6.4 billion generated by the Great Barrier Reef Marine Park in 2015-16, the majority of which comes from non-extractive industries.

This same erosion of protection is also proposed in Western Australia, where the government’s draft plan would reduce green zones by 43% across the largest marine parks in the region.

Zoning for the Gascoyne Marine Park as recommended by the Independent Review (left) and the new draft plan (right).
http://www.environment.gov.au/marinereservesreview/reports and https://parksaustralia.gov.au/marine/management/draft-plans/

Again, this is despite clear evidence that the fishing activities occurring in these areas are not compatible with conservation. Such proposals also ignore future pressures such as deep-sea mining.

The overall effect is summarised neatly by Frydenberg’s statement that the government’s plans will:

…increase the total area of the reserves open to fishing from 64% to 80% … (and) make 97% of waters within 100 kilometres of the coast open for recreational fishing.

Building ocean resilience

Science shows that full protection creates resilience by supporting intact ecosystems. Fully protected green zones recover faster from flooding and coral bleaching, have reduced rates of disease, and fend off climate invaders more effectively than areas that are open to fishing.

Green zones also contribute indirectly to the blue economy. They help support fisheries and function as “nurseries” for fish larvae. For commercial fisheries, these sanctuaries are more important than ever in view of the declines in global catches since we hit “peak fish” in 1996.

Of course it is important to balance conservation with sustainable economic use of our oceans. Yet the government’s new draft plan leaves a huge majority of Australia’s waters open to business as usual. It’s a brave Emperor who thinks this will protect our oceans.

The ConversationSo let’s put some real clothes on the Emperor and create a network of marine protection that supports our blue economy and is backed by science.

Jessica Meeuwig, Professor & Director, Marine Futures Lab, University of Western Australia and David Booth, Professor of Marine Ecology, University of Technology Sydney

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