EcoCheck: Australia’s Wet Tropics are worth billions, if we can keep out the invading ants

Steve Turton, James Cook University

Our EcoCheck series takes the pulse of some of Australia’s most important ecosystems to find out if they’re in good health or on the wane.

The largest area of tropical rainforest in Australia – the so-called Wet Tropics – is a narrow strip along the northeast coast of the continent, totalling about 2 million hectares.

It represents just 0.26% of the continent, but is crammed with hugely diverse landscapes: rainforests, sclerophyll forests, mangrove forests and shrublands, as well as areas of intensive agriculture and expanding urban rural population centres.

The Wet Tropics bioregion and World Heritage Area.
Peter Bannink/Australian Tropical Herbarium, Author provided

The Wet Tropics are home to a dizzying array of plants and animals. These include at least 663 vertebrate species, 230 butterflies, 135 different dung beetles and a remarkable 222 types of land snail. The area is teeming with more than 4,000 plant species, including 16 of the world’s 28 lineages of primitive flowering plant families.

In all, the Wet Tropics bioregion contains 185 distinct ecosystems. Of these, 18 are officially listed as endangered and 134 are of conservation concern.

Wild riches

Just under half of the region is covered by the Wet Tropics of Queensland World Heritage Area, the world’s second-most-irreplaceable natural world heritage area. A recent analysis listed it as the planet’s sixth-most-irreplaceable protected area in terms of species conservation, and its eighth-most-irreplaceable when considering only threatened species.

Yet despite its global conservation significance, the Wet Tropics was recently described by the International Union for the Conservation of Nature (IUCN) as a World Heritage Area of “significant concern”.

This is due to the threat posed to the area’s biodiversity and endemic plants and animals by invasive species, diseases and predicted climate change impacts. Only two other Australian world heritage properties are listed as “of concern”: the Great Barrier Reef and Kakadu National Park.

Given these concerns, one might expect research dollars to be flowing towards the Wet Tropics. In fact, the opposite is happening: the new National Environmental Science Program has pledged a paltry A$10,000.

Commonwealth funding for Wet Tropics research under successive programs: the CRC for Rainforest Research; the Marine and Tropical Sciences Research Facility (MTSRF); and the National Environmental Research Program (NERP). Under the National Environmental Science Program, only $10,000 has been allocated (not shown).
Rainforest CRC; MTSRF; NERP; CRC Reef Synthesis Report; Reef & Rainforest Research Centre, Author provided

While we’re talking money, it’s worth pointing out that the Wet Tropics are a goldmine. In its 2014-15 report, the Wet Tropics Management Authority calculated that this natural global asset is worth a whopping A$5.2 billion each year – roughly half of it from tourism.

A 2008 report found that the Wet Tropics create the greatest economic benefit of any of Australia’s natural world heritage properties, excluding the Great Barrier Reef. It found that every dollar spent on management costs earned an A$85 return in tourism spending. Even in purely economic terms that makes a pretty compelling case for conservation.

Climate and conservation

But there are question marks over the Wet Tropics’ future, not least because it is considered a hotspot for impacts from climate change. This is primarily due to the very large predicted declines in range size for almost all of the vertebrates that are unique to this part of the world, such as the iconic lemuroid ringtail possum. Climate change is likely to force some species to shift their geographic ranges, or face extinction.

Many of the species at greatest risk of extinction from climate change are confined to higher elevations and thus have very limited scope for dispersal. Of all the rainforest vertebrate species in the Wet Tropics, 30% live within the coolest 25% of rainforest. This gives them nowhere to go if things warm up. For unique species, that figure is even higher, with 45% living in these cooler areas.

Nor is the future too bright for many mountaintop plants, according to a study that modelled the future of suitable climate conditions for 19 species found only above 1,000 m elevation.

The study predicted that, by 2080, 84% of these species would have no suitable habitat anywhere in the Wet Tropics, and so would no longer be able to survive there.

Cat-ants-trophe

Watch out for these crazy guys.
John Tann/Wikimedia Commons, CC BY

The climate isn’t the only problem. Another is the accidental introduction of one of the world’s worst invasive species, yellow crazy ants, into two locations in the Wet Tropics.

Judging by the ants’ impacts elsewhere, this is an impending natural catastrophe. Based on the small amounts of research in the region so far, ecologists Lori Lach and Conrad Hoskin predict that a large invasion of yellow crazy ants could affect most of the animal species in the Wet Tropics.

These impacts could be direct – through predation and harassment – or indirect, such as by the removal of invertebrate prey or disruption of processes such as decomposition, pollination and seed dispersal. The potential for knock-on effects in a system as complex and interconnected as the Wet Tropics rainforest is very high.

We have only a small window of opportunity – perhaps five years at most – to keep the Wet Tropics safe from yellow crazy ants. The cost of failure by the Australian and Queensland governments is unimaginable. Yellow crazy ants are also a threat to agriculture and urban areas, so we should anticipate a successful and properly funded eradication campaign — mirroring the papaya fruitfly eradication efforts in the same region back in the mid-1990s.

If the siege can be repelled, we can hopefully go on enjoying the Wet Tropics – not to mention the money it generates – for many years to come.

Are you a researcher who studies an iconic Australian ecosystem and would like to give it an EcoCheck? Get in touch.

Steve Turton, Professor of Environmental Geography, James Cook University

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

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What does the science really say about sea-level rise?

John Church, CSIRO and Peter Clark, Oregon State University

A recent high-profile study led by US climatologist James Hansen has warned that sea levels could rise by several metres by the end of this century. How realistic is this scenario?

We can certainly say that sea levels are rising at an accelerating rate, after several millennia of relative stability. The question is how far and how fast they will go, compared with Earth’s previous history of major sea-level changes.

Seas have already risen by more than 20 cm since 1880, affecting coastal environments around the world. Since 1993, sea level has been rising faster still (see chapter 3 here), at about 3 mm per year (30 cm per century).

One key to understanding future sea levels is to look to the past. The prehistoric record clearly shows that sea level was higher in past warmer climates. The best evidence comes from the most recent interglacial period (129,000 to 116,000 years ago), when sea level was 5-10 m higher than today, and high-latitude temperatures were at least 2℃ warmer than at present.

The two largest contributions to the observed rise since 1900 are thermal expansion of the oceans, and the loss of ice from glaciers. Water stored on land (in lakes, reservoirs and aquifers) has also made a small contribution. Satellite observations and models suggest that the amount of sea-level rise due to the Greenland and Antarctic ice sheets has increased since the early 1990s.

Before then, their contributions are not well known but they are unlikely to have contributed more than 20% of the observed rise.

Together, these contributions provide a reasonable explanation of the observed 20th-century sea-level rise.

Future rise

The Intergovernmental Panel on Climate Change (IPCC) projections (see chapter 13 here) forecast a sea-level rise of 52-98 cm by 2100 if greenhouse emissions continue to grow, or of 28-61 cm if emissions are strongly curbed.

The majority of this rise is likely to come from three sources: increased ocean expansion; glacier melt; and surface melting from the Greenland ice sheet. These factors will probably be offset to an extent by a small increase in snowfall over Antarctica.

With continued emissions growth, it is entirely possible that the overall rate of sea-level rise could reach 1 m per century by 2100 – a rate not seen since the last global ice-sheet melting event, roughly 10,000 years ago.

Beyond 2100, seas will continue to rise for many centuries, perhaps even millennia. With continued growth in emissions, the IPCC has projected a rise of as much as 7 m by 2500, but also warned that the available ice-sheet models may underestimate Antarctica’s future contribution.

The joker in the pack is what could happen to the flow of ice from the Antarctic ice sheet directly into the ocean. The IPCC estimated that this could contribute about 20 cm of sea-level rise this century. But it also recognised the possibility of an additional rise of several tens of centimetres this century if the ice sheet became rapidly destabilised.

This could happen in West Antarctica and in parts of the East Antarctic ice sheets that are resting on ground below sea level, which gets deeper going inland from the coast. If relatively warm ocean water penetrates beneath the ice sheet and melts its base, this would cause the grounding line to move inland and ice to flow more rapidly into the ocean.

Several recently published studies have confirmed that parts of the West Antarctic ice sheet are already in potentially unstoppable retreat. But for these studies the additional rise above the IPCC projections of up to 98 cm by 2100 from marine ice sheet instability was more likely to be just one or two tenths of a metre by 2100, rather than several tenths of a metre allowed for in the IPCC report. This lower rise was a result of more rigorous ice-sheet modelling, compared with the results available at the time of the IPCC’s assessment.

How stable are ice sheets?

Ocean temperatures were thought to be the major control in triggering increased flow of the Antarctic ice sheet into the ocean. Now a new study published in Nature by US researchers Robert DeConto and David Pollard has modelled what would happen if you factor in increased surface melting of ice shelves due to warming air temperatures, as well as the marine melting.

Such an ice-shelf collapse has already been seen. In 2002, the Larsen-B Ice Shelf on the Antarctic Peninsula disintegrated into thousands of icebergs in a matter of weeks, allowing glaciers to flow more rapidly into the ocean. The IPCC’s predictions had considered such collapses unlikely to occur much before 2100, whereas the new study suggests that ice-sheet collapse could begin seriously affecting sea level as early as 2050.

With relatively high greenhouse emissions (a scenario referred to in the research literature as RCP8.5), the new study forecasts a rise of about 80 cm by 2100, although it also calculated that this eventuality could be almost totally averted with lower emissions. But when the model parameters were adjusted to simulate past climates, the Antarctic contribution was over 1 m by 2100 and as much as 15 m by 2500.

Greenland’s ice sheet is crucially important too. Above a certain threshold, warming air temperatures would cause surface melting to outstrip snow accumulation, leading to the ice sheet’s eventual collapse. That would add an extra 7 m to sea levels over a millennium or more.

The problem is that we don’t know where this threshold is. It could be as little as 1℃ above pre-industrial average temperatures or as high as 4℃. But given that present-day temperatures are already almost 1℃ above pre-industrial temperatures, it is possible we could cross this threshold this century, regardless of where exactly it is, particularly for high-emission scenarios.

Overall, then, it is clear that the seeds for a multi-metre sea-level rise could well be sown during this century. But in terms of the actual rises we will see in our lifetimes, the available literature suggests it will be much less than the 5 m by 2050 anticipated by Hansen and his colleagues.

The wider question is whether the ice-sheet disintegration modelled by DeConto and Pollard will indeed lead to rises of the order of 15 m over the coming four centuries, as their analysis and another recent paper suggest. Answering that question will require more studies, with a wider range of climate and ice-sheet models.

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John will be on hand for an Author Q&A between 2 and 3pm AEDT on Thursday, March 31, 2016. Post your questions in the comments section below.

John Church, CSIRO Fellow, CSIRO and Peter Clark, Distinguished Professor of Earth, Ocean, and Atmospheric Sciences, Oregon State University

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