Australia has just had its hottest October, and we can already say that human-caused climate change made this new record at least ten times more likely than it would otherwise have been.
But if we turn our eyes to the past, what role did climate change play in the broken records of 2014? Last year was the hottest on record worldwide, and came with its fair share of extremes.
As part of the annual extreme weather issue of the Bulletin of the American Meteorological Society released today, five papers by Australian authors including us, investigate the role of climate change in extreme weather in 2014.
Year of records
Australia was hit hard in 2014 (although perhaps not quite as hard as 2013, which was Australia’s hottest year ever).
The year started with a bang when the international spotlight fell on southeast Australia as Melbourne was baked by the infamous “Australian Open heatwave”. It led into 12 months that saw the country experience a 19-day heatwave in May, the hottest spring on record, and unusually hot weather in Brisbane during November, right in the middle of the G20 World Leaders Forum.
In August, a record high pressure system stalled to the south of Australia and brought some unusual winter weather, including severe frosts.
So did human-caused global warming play a role in this “weirding” of Australian weather?
Revealing the role of climate change
The annual extremes issue centres on one of the fastest developing areas in climate change research, the role of climate change in recent extreme weather events.
While the link between human activities and climate change has been firmly established for several decades, attributing a single event to human influence isn’t easy. This is because individual events may be the result of natural climate variation.
To get to the heart of how climate change is influencing these extreme events, scientists try to determine how much more likely individual extremes are as a result of climate change. Using climate models they compare the world of today with a parallel world without human greenhouse gas emissions.
These scenarios are often run on models thousands of times in an effort to recreate events that are of a similar scale. By comparing the results of modelled climates with and without human-produced greenhouse gases, researchers can determine how much more likely it is that an extreme weather event occurred as a result of human-caused global warming.
This approach is similar to the way epidemiologists investigate whether smoking increases the likelihood of lung cancer.
Interestingly, there was a significant citizen science role in three of the Australian peer-reviewed studies reported in the extremes issue. Using a large number of climate simulations run on thousands of home computers as part of the Weather@home project, the scientists were able to examine local-scale extreme events such as the January heatwave in Melbourne.
What we found
The first study, led by Mitchell Black, focused on the prolonged heatwave in southeast Australia in January 2014. During this event Adelaide recorded five consecutive days above 42°C (13–17 January) while Melbourne recorded four consecutive days above 41°C (14–17 January) during the Australian Open tennis tournament.
This study found that human influence very likely increased the chance of prolonged heatwaves in Adelaide by at least 16%. Meanwhile, the influence for Melbourne was less clear.
The second study, led by Andrew King, examined an extreme temperature event caught in the spotlight of international media attention – the unseasonably hot weather in Brisbane during the G20 summit in mid-November. While the hot temperatures were not record-breaking in Brisbane at this time, they were well above average.
This study found that human influence increased the likelihood of hot (above 34°C) and very hot (above 38°C) November days in Brisbane by at least 25% and 44%, respectively.
The third study, led by Michael Grose at CSIRO, examined the exceptionally high surface pressure to the south of Australia during August 2014. This was associated with severe frosts in southeast Australia, lowland snowfalls in parts of Tasmania, and reduced rainfall in the southern parts of both Australia and New Zealand.
The findings suggested that the likelihood of these pressure anomalies had roughly doubled due to human-induced climate change.
The remaining two studies published today used independent sets of climate model simulations.
The fourth study, led by Sarah Perkins-Kirkpatrick from the University of New South Wales, investigated the late-autumn heatwave (May 8-26) that resulted in Australian-averaged maximum temperatures being 2.52°C above the monthly average. Although this heat event occurred during the cooler months, events of this nature are important because they can affect agricultural productivity through changing crop cycles.
The study found that this kind of cool-season heatwave was 23 times more likely as a result of increased greenhouse gasses.
Pandora Hope from the Australian Bureau of Meteorology led the final study, which examined Australia’s hottest spring on record. The study concluded that the record heat would likely not have occurred without increases in atmospheric carbon dioxide over the last 50 years working in concert with anomalous atmospheric patterns.
Year on year, in the extremes issues and through various other investigations reported in the peer-reviewed literature, these attribution studies continue to show that climate change is no longer something that will occur in the future. The rise of human-caused global warming is here, now, and it is already causing changes to extreme weather events that we can see and feel.
Mitchell Black, PhD Candidate, University of Melbourne; Andrew King, Climate Extremes Research Fellow, University of Melbourne, and David Karoly, Professor of Atmospheric Science, University of Melbourne
Some Australian birds are pushing out other species, and even damaging trees. Noisy and bell miners are two of Australia’s most aggressive bird species. Found throughout eastern Australia, in recent years their numbers have increased at the expense of our smaller birds.
Both species are spreading to new areas, largely due to human destruction of habitat. Noisy miners are able to invade areas where habitat has been modified, particularly gardens.
Bell miners, meanwhile, can invade areas that have invasions of weeds in the understorey such as blackberry and lantana that they use for nesting.
The good news is we can help stop the spread of these birds, by putting native plants in our gardens.
Good birds gone bad
Both species of these miners (genus Manorina) have been found to reduce bird diversity through their aggressive behaviour, and have been associated with eucalypt dieback.
Human disturbance has been linked to increasing numbers of noisy miners. One study in the box-ironbark forests of southeast Australia, found that noisy miners an move into areas of smaller fragments and unhealthy trees.
They then chase away other birds, reducing the number of species and potentially having knock-on effects on ecosystems. The problem is so serious that noisy miners are listed as a national threatening process.
More research is needed to find out why bell miners are becoming more common. But our research has found that bell miners show similar behaviour to noisy miners. They have a distinctive call that travels for tens of metres through the forest.
Bell miners cause Bell Miner Associated Dieback in trees. It is thought that their feeding and breeding behaviours lead to the death of eucalypts on the east coast of Australia. They also take over habitat that would be used by other birds.
Are the birds to blame?
Where miners are normally found in lower numbers, disturbances by people can tip the balance in their favour. This includes increasing noise levels, removing corridors of connecting native vegetation, creating gardens with exotic plants, building cities, houses, parks, logging and introducing invasive species that create thick understories.
These disturbances increase the habitat available for these two species, allowing them to increase in number and drive out the smaller birds that compete for their food sources.
Noisy miners particularly favour open areas that don’t have thickets of shrubs of smaller trees underneath the canopy. Conversely, bell miners prefer thick understoreys, particularly those create by introduced weeds such as lantana.
So if we are causing these birds to increase in number, how can we reduce their numbers and re-create the original habitat where all species could co-exist?
Build a bird-friendly garden
You need to create a multi-layered habitat of ground covers, small and medium shrubs, and trees that provide food and shelter locations all year for a variety of species.
These plant species need to have diverse structures, and should be close together to form dense, protective thickets, including climbers within medium-to-tall shrubs and trees, nectar-bearing and seed-bearing plants. Mulch can also encourage insect life for insectivorous birds.
Plants should also be local species that grow naturally in the area and are suited to the climate. Native birds that live in the area will then visit your garden as another food source in their territory.
Reducing weeds in your garden and neighbouring bushland (many weeds are derived from garden plants) can help native species. General natives can also be planted if you can’t find local natives in your local nursery.
Even in gardens where noisy miners dominate, smaller birds can survive in a dense understorey.
Meanwhile, a thin midstorey with fewer leaves may help to reduce bell miner abundance, as suggested by our recent study near Kyogle, New South Wales.
You should also consider the timing of flower and fruit production, to ensure that there is always food available for birds. You should also remove fruiting plants such as cotoneaster and blackberry that attract predators such as currawongs, to help reduce predation on smaller bird species.
Using chemical-free weed and pest control and mulching garden waste can also increase the food available for birds.
Lawns can also be replaced with native grasses that produce seed to attract finches and other seed-eaters such as crimson rosellas. Birds also need fresh water, which you can provide with a pond or bird bath. This should be placed within vegetation to ensure birds feel safe from predators.
Why are native gardens important?
Local biodiversity can be maintained by native gardens, ensuring long-term ecological sustainability. Small birds and other wildlife benefit from planting native species.
Many species are negatively affected by the current structure of gardens such as lawns, few scattered trees and the placement of concrete and houses without any access to nesting habitat.
Gardening in Australia needs to be changed to favour more native species and provide structure on a landscape scale that includes a variety of gardens.