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Global warming has already increased the risk of major disruptions to Pacific rainfall, according to our research published today in Nature Communications. The risk will continue to rise over coming decades, even if global warming during the 21st century is restricted to 2℃ as agreed by the international community under the Paris Agreement.

In recent times, major disruptions have occurred in 1997-98, when severe drought struck Papua New Guinea, Samoa and the Solomon Islands, and in 2010-11, when rainfall caused widespread flooding in eastern Australia and severe flooding in Samoa, and drought triggered a national emergency in Tuvalu.

These rainfall disruptions are primarily driven by the El Niño/La Niña cycle, a naturally occurring phenomenon centred on the tropical Pacific. This climate variability can profoundly change rainfall patterns and intensity over the Pacific Ocean from year to year.

Rainfall belts can move hundreds and sometimes thousands of kilometres from their normal positions. This has major impacts on safety, health, livelihoods and ecosystems as a result of severe weather, drought and floods.

Recent research concluded that unabated growth in greenhouse gas emissions over the 21st century will increase the frequency of such disruptions to Pacific rainfall.

But our new research shows even the greenhouse cuts we have agreed to may not be enough to stop the risk of rainfall disruption from growing as the century unfolds.

Changing climate

In our study we used a large number of climate models from around the world to compare Pacific rainfall disruptions before the Industrial Revolution, during recent history, and in the future to 2100. We considered different scenarios for the 21st century.

One scenario is based on stringent mitigation in which strong and sustained cuts are made to global greenhouse gas emissions. This includes in some cases the extraction of carbon dioxide from the atmosphere.

In another scenario emissions continue to grow, and remain very high throughout the 21st century. This high-emissions scenario results in global warming of 3.2-5.4℃ by the end of the century (compared with the latter half of the 19th century).

The low-emissions scenario - despite the cuts in emissions - nevertheless results in 0.9-2.3℃ of warming by the end of the century.

Increasing risk

Under the high-emissions scenario, the models project a 90% increase in the number of major Pacific rainfall disruptions by the early 21st century, and a 130% increase during the late 21st century, both relative to pre-industrial times. The latter means that major disruptions will tend to occur every four years on average, instead of every nine.

The increase in the frequency of rainfall disruption in the models arises from an increase in the frequency of El Niño and La Niña events in some models, and an increase in rainfall variability during these events as a result of global warming. This boost occurs even if the character of the sea-surface temperature variability arising from El Niño and La Niña events is unchanged from pre-industrial times.

Although heavy emissions cuts lead to a smaller increase in rainfall disruption, unfortunately even this scenario does not prevent some increase. Under this scenario, the risk of rainfall disruption is projected to be 56% higher during the next three decades, and to remain at least that high for the rest of the 21st century.

The risk has already increased

While changes to the frequency of major changes in Pacific rainfall appear likely in the future, is it possible that humans have already increased the risk of major disruption?

It seems that we have: the frequency of major rainfall disruptions in the climate models had already increased by around 30% relative to pre-industrial times prior to the year 2000.

As the risk of major disruption to Pacific rainfall had already increased by the end of the 20th century, some of the disruption actually witnessed in the real world may have been partially due to the human release of greenhouse gases. The 1982-83 super El Niño event, for example, might have been less severe if global greenhouse emissions had not risen since the Industrial Revolution.

Most small developing island states in the Pacific have a limited capacity to cope with major floods and droughts. Unfortunately, these vulnerable nations could be exposed more often to these events in future, even if global warming is restricted to 2℃.

These impacts will add to the other impacts of climate change, such as rising sea levels, ocean acidification and increasing temperature extremes.

This research was supported by the National Environmental Science Programme and the Australian Climate Change Science Programme.

Brad Murphy, Christine Chung, François Delage, and Hua Ye do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

Dingoes are often promoted as a solution to Australia's species conservation problems. Dingo image from www.shutterstock.com

Dingoes have often been hailed as a solution to Australia’s threatened species crisis, particularly the extreme extinction rate of the country’s small mammals.

But are dingoes really the heroes-in-waiting of Australian conservation? The truth is that no one knows, although our recent research casts a shadow over some foundations of this idea.

The notion of dingoes as protectors of Australian ecosystems was inspired largely by the apparently successful reintroduction of wolves into Yellowstone National Park in the United States. But Australia’s environments are very different.

Cascading species

To understand the recent excitement about wolves, we need to consider an ecological phenomenon known as “trophic cascades”. The term “trophic” essentially refers to food, and thus trophic interactions involve the transfer of energy between organisms when one eats another.

Within ecosystems, there are different trophic levels. Plants are typically near the base; herbivores (animals that eat plants) are nearer the middle; and predators (animals that eat other animals) are at the top.

The theory of trophic cascades describes what happens when something disrupts populations of top-order predators, such as lions in Africa, tigers in Asia, or Yellowstone’s wolves.

The wolves’ decline allowed herbivores, such as elk, to increase. In turn, the growing elk population ate too much of the shrubby vegetation alongside rivers, which, over time, changed from being mostly willow thickets to grassland. Then another herbivore – beavers – that relies on willows went locally extinct. This in turn affected the ecology of the local streams.

Wolves play a key role in Yellowstone’s ecosystems. Wolf image from www.shutterstock.com

Without beavers to engineer dams, local waterways changed from a series of connected pools to eroded gutters, with huge flow-on effects for smaller aquatic animals and plants.

Now, the reintroduction of wolves appears to have reduced the impact of elk on vegetation, some riparian areas have regenerated, some birds have returned and there are signs of beavers coming back. That said, wolf reintroduction has not yet fully reversed the trophic cascade.

Comparing apples with quandongs

Sturt National Park, in the New South Wales outback, has been nominated as an experimental site for reintroducing dingoes. Recently, we compared the environment of Sturt with Yellowstone to consider how such a reintroduction might play out.

These regions are clearly very different. Both are arid, but that is where the similarity ends. Yellowstone has a stable climate and nutrient-rich soils, sits at high altitude and features diverse landscapes. Precipitation in Yellowstone hasn’t dropped below 200mm per year in more than a century.

Herds of bison in Yellowstone National Park. Helen Morgan

Yellowstone’s precipitation falls largely as heavy winter snow. Each spring the snowmelt flows in huge volumes into rivers, streams and wetlands across the landscape. This underpins a predictable supply of resources which, in turn, triggers herbivores to migrate and reproduce every year.

These predictable conditions support a wide range of carnivores and herbivores, including some of North America’s last-remaining “megafauna”, such as bison, which can tip the scales at over a tonne. Yellowstone also has many large predators – wolves, grizzly bears, black bears, mountain lion, lynx and coyotes all coexist there – along with a range of smaller predators too.

Predators in Yellowstone can be sure that prey will be available at particular times. The environment promotes stable, strong trophic links, allowing individual animals to reach large sizes. This strong relationship between trophic levels means that when the system is perturbed – for instance, when wolves are removed – trophic cascades can occur.

Unlike Yellowstone, arid Australia is dry, flat, nutrient-poor and characterised by one of the most extreme and unpredictable climates on Earth. The yearly rainfall at Sturt reaches 200mm just 50% of the time.

Australia’s Sturt Desert has a highly unpredictable climate. Helen Morgan

Australia’s arid ecosystems have evolved largely in isolation for 45 million years. In response to drought, fire and poor soils, arid Australia has evolved highly specialised ecosystems, made up of species that can survive well-documented “boom and bust” cycles.

Unlike the regular rhythm of Yellowstone life, sporadic pulses of water and fire affect and override the trophic interactions of species, between plants and herbivores, and predators and their prey. Our native herbivores travel in response to patchy and unpredictable food sources in boom times. But however good the boom, the bust is certain to follow.

Unpredictable but inevitable drought weakens trophic links between predators, herbivores and plants. Individuals die due to lack of water, populations are reduced and can only recover when rain comes again.

Our arid wildlife is very different from Yellowstone’s too. Our megafauna are long gone. So too are our medium-sized predators, such as thylacines.

Today, arid Australia’s remaining native wildlife is characterised by birds, reptiles and small mammals, along with macropods that are generally much smaller than the herbivores in Yellowstone.

Our predators are small and mostly introduced species, including dingoes, foxes and cats. None is equivalent to wolves, mountain lions or bears, which can reach more than three times the weight of the largest dingo. Wolves are wolves, and dingoes are dogs.

Wolves in dingo clothes?

What does all this mean for Australia? Yellowstone’s stable climate means that there are strong and reliable links between predators, prey and plants. By comparison, arid Australia’s climate is dramatically unstable.

This raises the question of whether we can reasonably expect to see the same sorts of relationships between species, and whether dingoes are likely to help restore Australia’s ecosystems.

We should conduct experiments to understand the roles of dingoes and the impacts of managing them. How we manage predators, including dingoes, should be informed by robust knowledge of local ecosystems, including predators’ roles within them.

What we shouldn’t do is expect that dingoes will necessarily help Australia’s wildlife, based on what wolves have done in snowy America. The underlying ecosystems are very different.

Many people are inspired by the apparently successful example of wolves returning to Yellowstone, but in Australia we should tread carefully.

Rather than trying to prove that dingoes in Australia are just as beneficial as wolves in Yellowstone, we should seek to understand the roles that dingoes really play here, and work from there.

Helen Morgan receives funding from the Keith and Dorothy Mackay Travelling Scholarship, University of New England, the Holsworth Wildlife Endowment Trust and Invasive Animals CRC

Guy Ballard receives funding from the Invasive Animals Cooperative Research Centre, NSW Local Land Services and the NSW National Parks & Wildlife Service.

John Thomas Hunter does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

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