Five degrees hotter?
IT'S 2100. A sci-fi movie version of the future is finally here – flying cars, robots, choking pollution. Oh, and the planet is 5 degrees hotter than it was at the turn of the millennium. It’s nearly 90 years since scientists warned (again) that the planet could warm by between 4 and 6 degrees if we didn’t cut greenhouse gas emissions. We didn’t, and it did.
The average global temperature, for night and day, is now 19 degrees, up from 14 degrees at the turn of the 20th century.
The best scientific estimates suggest that the last time it was this hot was during the Eocene, more than 30 million years ago, and long before humans turned up. Back then, temperatures rose gradually over many thousands of years. We've watched it happen in 100.
What is life like? Australia is both unrecognisable and strangely familiar. In the south-east, where the population is increasingly concentrated, it is hot and dry. If the average day is warmer, the warmest days are that much hotter again. Daily temperatures above 35 degrees are more frequent: there are twice as many of these scorchers in Sydney and Melbourne than a century ago.
Meanwhile, the colder days have melted away like the snow at Thredbo and Mount Buller. This is a relief in winter, but not much fun in summer, unless you live in Tasmania, which has inherited Sydney's climate. Sydney is more like Rockhampton: too hot and humid for too much of the year.
Weather similar to Victoria's summer of 2009 – when scientists estimated that 374 people, mostly elderly, died due to heat stress as the temperature topped 43 degrees three days straight – has become more common. And people now die because of heat-related stress throughout the year. Temperature-related deaths have jumped in Western Australia, tripled in Queensland and increased nearly sevenfold in the Northern Territory.
Rainfall is down more than 35 per cent in Melbourne across the year, and has halved in summer. But when it rains, it rains harder. There are more floods, more severe wind storms, more bushfires and more frequent droughts.
The warming has reduced the number of people that die in southern states in winter. But more Australians are dying due to extreme heat than are surviving because of warmer winters.
Mosquito and water-borne diseases such as dengue fever have migrated south to New South Wales. The number of people hurt or killed during extreme weather events, and the amount of property damaged, has also increased.
This hasn't escaped the attention of the insurance industry, which has escalated premiums at such a rate that it has priced most people out of the market, leaving more of the population reliant on governments to step in if disaster strikes. Taxes have been raised to foot the bill.
Water has also become much more expensive. The desalination plants that seemed premature early last century are now used daily in NSW, Victoria, South Australia and southern Western Australia – and we've built more. We have also got used to drinking and bathing in recycled sewerage water.
Lots of farms have shut down – more than 90 per cent of dairy and fruit and vegetable production from irrigated farms in the Murray-Darling Basin has ceased. Instead, crops previously grown in hotter areas such as sorghum are planted in winter. It had been hoped that the north of Australia could be transformed into the "food basin of Asia" as tropical weather spread south, bringing a more intense wet season. But an increasingly temperamental monsoon means these crops are also at risk of drying up when "the wet" doesn't arrive.
The government has intervened to ban food exports, just as Russia was mocked for doing during droughts early last century. The states have started stockpiling food, fearing shortages will lead to riots. Countries are increasingly focusing inwards – other nations be damned.
Food production has become more technical. Concerns about genetically modified foods largely evaporated as the need to feed people took precedence. As the World Bank predicted long ago, Australian farms no longer yield anything like what they once did. Those that have survived are bigger and (like everything) more mechanised.
Wheat production has plummeted and the wine industry has shrunk, with fewer vineyards and poorer grape quality. Where mining was once Australia's fly-in, fly-out industry, now it is agriculture.
Small towns in country Australia are on their knees. People are clustered more than ever in big cities. The divide between the wealthy, living in inner-suburban bubbles, and the poor in the disconnected outer suburbs, has been cemented.
The economy has taken a hit as export markets have declined. Mining, and particularly fossil-fuel industries, has suffered as the world belatedly looked for new forms of energy. Australia's tourism industry, once worth $35 billion a year, has suffered from the disappearance of the Great Barrier Reef and the snowfields.
Regions have also been hit by the rising intensity of bushfires. The lure of a "tree-change" is gone: now, the ideal is living in a secure, heavily insulated and airconditioned high-rise built from sturdy but light-weight and fire-resistant fibres.
Where summer was once a season to be celebrated at the beach, for many people it is increasingly spent indoors, with outdoor work timed to avoid searing afternoon summer temperatures across most of the country.
The Australian landscape has suffered: more than a third of native species have died, more of the outback has eroded to desert and more than half of all eucalypt habitat is gone forever. The tropics – once home to 700 species of plants, 13 species of mammals found nowhere else on the planet, a quarter of Australia's frogs, a third of its freshwater fish and nearly half of its birds – have been devastated.
Along the coast, much of the country's iconic reef has been killed off by a combination of heat and changes in ocean chemistry. Oceans have become what is described as more acidic, but in reality the water is less alkaline. Ocean ecosystems have been ruptured, with scientists warning a mass extinction is under way. This has devastated commercial fishing and coastal regional communities.
Meanwhile, coastal communities, suburbs and tourism have been further hit by sea-level rise, now approaching a metre this century. Metres more are locked-in for coming centuries as the guaranteed melting of major ice sheets slowly unfolds. An old rule of thumb says that for every centimetre of sea-level rise, the shoreline retreats by 50 centimetres to a metre.
While the retreat of the shoreline has been inconsistent due to seawalls and other defensive projects, once cherished beaches such as Bondi and Bells have eroded away and bay and seaside suburbs have been regularly inundated following worsening storms surges . The damage from surges associated with rising seas reaches tens of billions of dollars. Eventually, authorities considered closing off Sydney Harbour and Port Phillip to protect coastal properties from the ocean.
At Sydney airport, one runway and several taxiways are occasionally swamped.
While Australia has felt the impact of rising seas, the damage is nothing compared with cities in Asia, where tens of millions – some say hundreds of millions – of people have been displaced by drought and rising seas and are looking for a new home. If you thought the public debate in Australia over asylum seekers in the early 21st century was acrimonious, you haven't seen anything yet.
THIS scenario is, of course, just one possible vision of the future. Whether it is alarming, alarmist or conservative will depend on your perspective. It is drawn from studies by and interviews with a dozen experts from the Bureau of Meteorology, CSIRO, leading Australian universities and major consultancies. Some of it is based on published research, some educated speculation about how people may respond.
It does not factor in the potential for complicated and disastrous conflicts over resources between stressed nations. Nor does it consider the obvious solution that would head it off: that the world eventually agrees at meetings like the current United Nations summit in Doha to rapidly reduce emissions.
Many scientists interviewed stressed that the biggest issue facing the planet may be the pace of warming and climate change – unlike anything the Earth has seen in tens of millions of years. They warned it could make climate systems increasingly volatile, with the potential for large and sudden regional changes.
The 5-degree projection is drawn from a report released this week by a consortium of scientists calling themselves the Global Carbon Project. They found emissions have increased 54 per cent since 1990, putting the world on-track to be between 4 and 6 degrees hotter by 2100 unless action is taken.
Published in the journal Nature Climate Change, the report found the current emissions trajectory was most likely to mean an average global temperature rise of between 4.2 and 5 degrees.
It followed a separate, World Bank-commissioned study warning that a 4-degree leap was possible this century – even if current pledges to cut emissions are met.
Although the studies were undertaken and backed by serious bodies, not all scientists have the same level of confidence in computer-model projections.
As Australian National University Professor Tony McMichael, who studies the impact of climate change on health, notes: "This is an unusual task for science and it still draws the ire of some scientists, who say science is about learning from the past and present, not predicting the future."
But he says it is a "folly to be held down by this orthodoxy". "One way or another, we have to address this issue and that includes making our best assessments of what the real-world evidence and complex computer models can tell us about the range of likely outcomes," he says.
How do scientists assess the sensitivity of the climate to rising emissions? It is not as simple as just doing the sums on how much heat the extra gases will trap, and watching the land-based temperature record rise smoothly on a chart.
The human-induced greenhouse effect that traps heat in the lower atmosphere, first discovered in the 19th century, must be considered in the context of a chaotic melange of weather patterns, changes in solar radiation and regional influences such as the El Nino, La Nina cycle.
"If you look at a temperature chart, it is full of noise," says Professor Will Steffen, executive director of the Australian National University Climate Change Institute and a member of the government's Climate Commission. "You have to factor out the other influences . . . before you start seeing a clear trend line that relates to the carbon dioxide."
While emissions are rising rapidly, the atmospheric concentration of carbon dioxide is increasing by about 2 parts per million a year.
The average concentration over the 800,000 years before industrialisation – the period when modern humans evolved – has fluctuated between about 170 and 300 parts per million. Since industrialisation, it has risen to about 392 parts per million. On top of this, melting permafrost, farming and mining have released significant amounts of methane, another potent greenhouse gas.
Complex computer climate models predict where this steady rise will take us within the range of variability possible due in part to natural factors.
Most models used to estimate past and future climate change agree that doubling atmospheric carbon dioxide would raise average temperatures around the world by about 3 degrees. They add that the change could be 2 degrees higher than that, or perhaps 1 degree lower.
Real-world observations, drawn from bubbles of air trapped in ancient ice or measuring the amount of heat the ocean has soaked up, give a slightly different value for doubling atmospheric carbon dioxide – a rise of between 1.8 and 3.5 degrees.
Assessing the true measure of "climate sensitivity" is therefore an area of some uncertainty, though the gap between models and the geological record has narrowed. Unfortunately, there is no control group on which scientists can test possible scenarios – there is only one experiment, and we are living in it.
According to David Karoly, an atmospheric scientist at Melbourne University and a lead author with the Intergovernmental Panel on Climate Change, global projections may not give a true picture of how we will experience global warming.
"The problem we have is that, even if our best estimate is 4 degrees of warming this century, that is a global average and most of the globe is water," he says. "Four degrees on average means probably 3 degrees over the oceans, and 5 or 6 degrees on average over the land."