Since 1880, the average global temperature has increased by 0.8°℃, with large changes in rainfall redistribution. With these changing conditions upon us, and set to continue, gardeners will have to alter the way they do things.
Gardeners face the same changing conditions. If you look at the back of a seed packet, there is often a map showing the regions where these particular plants thrive. But with a rapidly changing climate, these regions are shifting.
In the future we will need to be more thoughtful about what we plant where. This will require more dynamic information and recommendations for gardeners.
The shifting climate
Changes in altitude significantly affect the temperature. As you walk up a hill, for every 100 metres of altitude you gain, the temperature drops by an average of 0.8℃.
Changes in latitude obviously have a bearing on the temperature too. It gets cooler as you move towards the poles and away from the Equator. An accurate rule of thumb is difficult to derive, because of the number of interacting and confounding factors. But generally speaking, a shift of 300 km north or south at sea level equates to roughly a 1℃ reduction in average temperature.
This means that due to warming over the past century or so, Adelaide now experiences the climate previously found in Port Pirie, whereas Sydney’s climate is now roughly what was previously found halfway to Coffs Harbour. The temperature difference is equivalent to a northward shift of approximately 250 km or drop in altitude of 100 m.
At current climate change trajectories, these shifts are set to continue and accelerate.
We have also seen some major shifts in the distribution of animal and plant communities over the past 50 years. Some of the most responsive species are small mobile insects like butterflies, but we have also seen changes among plants.
But while entire populations may be migrating or adapting, plants that grow in isolated conditions, such as fragmented bush remnants or even gardens, may not have this option. This problem is perhaps most acute for long-lived species like trees, many of which germinated hundreds of years ago under different climatic conditions. The climate conditions to which these old plants were best adapted have now changed significantly – a “climate lag”.
Using such old trees as a source of seed to grow new plants in the local area can potentially risk establishing maladapted plants. But it’s not just established varieties that run this risk.
The habitat restoration industry has recognised this problem. Many organisations involved in habitat restoration have changed their seed-sourcing policies to mix seeds collected from local sources with those from more distant places. This introduces new adaptations to help cope with current and future conditions, through practices known as composite or climate-adjusted provenancing.
The shifting climate and your garden
Gardeners can typically ameliorate some of the more extreme influences of global warming. They can, for example, provide extra water or shade on extremely hot days. Such strategies can allow plants to thrive in gardens well outside their natural climatic envelope, and have been practised by gardeners around the world for centuries.
But with water bills rising and the need to become more sustainable, we should think more carefully about the seeds and seedlings we plant in our gardens. The climate envelope we mentioned earlier is shifting rapidly.
We will need to start using seeds that are better adapted to cope with warmer and, in many cases, drier conditions. Typically, these plants have thinner leaves or fewer pores. This requires more information on the location and properties of the seeds’ origin, and a more detailed matching of diverse seed sources to planting location.
As the climate continues to change we will also need to introduce species not previously grown in areas, using those that are better adapted to the increasingly changed climatic conditions.
Plenty of tools are now available to help guide seed collection and species selection for planting. These include those offered through the National Climate Change Adaptation Research Facility and the Atlas for Living Australia, for instance.
But these resources are often aimed at expert or scientific audiences and need to be made more accessible for guiding gardening principles and plant selection for the public. The information needs to be intuitive and easy to understand. For example, we should produce lists of species that are likely to decline or benefit under future climate conditions in Australia’s major cities and towns, along with future growing areas suitable for some of our most popular garden species.
This won’t just be useful for a backyard gardener, either. Many exciting new gardening initiatives are being proposed, including rooftop gardens, which promote species conservation, carbon sequestration and heat conservation, and future city designs, which incorporate large-scale plantings and gardens for therapeutic benefits. All of these activities need to take the shifting climate into account, as well as the need to change practices to keep up with it.
After several dry years, vegetation across much of Australia received much-needed rains in 2016. But this broad pattern of improvement belies some major environmental damage in parts of the country – particularly in Tasmania, which was scorched by bushfire, the Gulf Coast and Cape York, which missed out on the rains’ return, and on the Great Barrier Reef, which suffered massive coral bleaching.
That is the conclusion of our report on Australia’s Environment in 2016, released today. It’s a summary of the state of the nation’s environmental indicators, which we compiled by analysing huge amounts of satellite imagery, ground data, and water and landscape modelling.
The report and the accompanying Australia’s Environment Explorer website summarise those data into graphs and plots for 13 environmental indicators. With most data extending back to at least the year 2000, this makes it possible to see how the environment is changing.
The overall story is one of rainfall boom after four years of bust. The national average rainfall in 2016 was again well above average, albeit not quite as much as in the bumper years 2010-11.
Our report last year showed soil moisture conditions had reached a six-year low in 2015, as Australia was dragged back towards the conditions experienced during the Millennium Drought.
The rains of 2016 seem to have put at least a temporary end to this. Over the past year the soil moisture in Australia’s landscapes has bounced back to levels not seen since 2012. Vegetation growth, leaf matter and soil protection all followed the same pattern.
Despite major bushfires in Tasmania in January, there were fewer fires overall than in previous years. As a result, carbon emissions from bushfires were the lowest since 2010, meaning that 2016 was overall a good year for land-based carbon emissions.
Scorecard: winners and losers
We combined the data to produce an overall “environmental scorecard” for each state and territory, as well as for the nation as a whole. Inevitably, this introduces subjective judgements, but because so much of the environment’s health is linked to water availability, the overall pattern would remain similar even if we were to calculate the index differently.
The national environmental score increased to above average (6.7), but the improvements were uneven. Scores fell in Tasmania and the Northern Territory, in the aftermath of dry conditions that had already started in 2015 or before, whereas other states improved by varying amounts.
Large parts of Queensland had been suffering through several years of drought but bounced back with good rains and growth conditions. Despite this, much of the state remains officially drought-declared – although not, ironically, Cape York. Such contrasts are not unusual; it often takes more than a year of good rain for drought declarations to be lifted.
Meanwhile, the Channel Country and many of the Murray-Darling Basin rivers received their best flows since the Big Wet of 2010–12, replenishing floodplains and wetlands along the way.
The bad news
Continued dry conditions in northwestern Tasmania created the conditions for massive bushfires in the first two months of 2016. The fires affected an estimated 95,000ha across the state, including 18,000ha of vulnerable alpine ecosystems in the Tasmanian Wilderness World Heritage Area. Although that is less than 1% of the total World Heritage Area, the ancient vegetation may have changed permanently. Characteristically for Australia, the fires were followed by a deluge, restoring soil moisture levels from May onwards but also causing major flood damage.
In the Top End, areas around the Gulf of Carpentaria missed out on the rains and continued a dry run that has lasted for four years in some places. Cape York was left high and dry, with historically low rainfall records at some locations.
Mangrove trees died in large numbers along 700km of coast on the Gulf of Carpentaria. The record temperatures and ongoing dry conditions were a likely factor. Mangroves provide breeding grounds for many sea organisms and protect the coast from erosion, and their demise may cause knock-on effects into the future.
To Australia’s east, high sea temperatures played an important role in large-scale bleaching on the Great Barrier Reef. Reefs and mangroves have been wiped out and recovered before, such as after cyclones. But the sheer scale of last year’s damage was unusual and set against an unmistakable climate warming trend. The big question is whether these ecosystems will be able to recover before suffering the next setback.
So, while all of our national headline environmental indicators suggest signs of general recovery, not everything is easily summarised or understood. The full consequences of the damage done to the Great Barrier Reef, tropical mangrove forests and Tasmania’s wilderness may take several years to become clear.
Worryingly, the factors that drove them into decline are likely to become stronger in future. Add to that the record heatwaves this year, and it becomes clear that climate change will not just quietly disappear.
Albert Van Dijk, Professor of Water Science and Management, Fenner School of Environment & Society, Australian National University and David Summers, Research academic, Fenner School of Environment & Society, Australian National University