CSIRO Staff Ponder ­Industrial Action Over Climate Shake-Up

The Australian - John Ross

CSIRO chief executive Larry Marshall in Canberra.

CSIRO staff have taken the first steps towards ­industrial action, and the Bureau of Meteorology has warned of gaps in joint weather research programs, as the fallout from the science agency’s restructure continues.
Climate scientists yesterday filed out of a Melbourne conference to stage a protest over the CSIRO’s plans, which threaten up to 350 jobs, as the agency discontinues some of its modelling work to focus on mitigation and adaptation to climate change. The protesters included former CSIRO researcher Penny Whetton, who shirtfronted Malcolm Turnbull during Sunday’s open day in the grounds of The Lodge.
Dr Whetton, whose partner is Greens senator Janet Rice, told The Australian it would take 20 years to rebuild the expertise now in the firing line. “If there were resources some years down the track to re-establish that capability, money couldn’t buy it,” she said.
The BoM yesterday said there would be “holes” in joint programs if the CSIRO pulled out. “CSIRO aren’t doing everything but they play a very significant role,” chief executive Rob Vertessy said.
Peter Stott, a visiting scientist from the British Met Office, said the decision breached “good faith” in an international project to monitor oceanic conditions.
Dr Stott said the project was an “altogether” enterprise. “If one country withdraws support, somebody may be able to step in. But you need the expertise that Australia has built up because of its position in the southern hemisphere. With research expertise, you can’t just stop it and then start again in a few years’ time.”
On Friday, the CSIRO Staff Association notified management of a dispute, claiming it had breached consultation obli­gations in the staff agreement. Secretary Sam Popovski said the association would today decide whether to refer the dispute to the Fair Work Commission.

Links

• CSIRO head Larry Marshall defends climate research cuts as angry scientists protest in Melbourne
• Heat to stay on CSIRO climate cuts amid claims Malcolm Turnbull was 'blindsided'
• 'Misleading, inaccurate and in breach of Paris': CSIRO scientist criticises cuts

Australia Adds New Colour To Temperature Maps As Heat Soars

The Guardian - Damian Carrington

Forecast temperatures are so extreme that the Bureau of Meteorology has had to add a new colour to its scale. It is a sign of things to come

Australian Bureau of Metereology temperature map - with a new colour for 52-54C. Photograph: BOM.

Global warming is turning the volume of extreme weather up, Spinal-Tap-style, to 11. The temperature forecast for next Monday by Australia's Bureau of Meteorology is so unprecedented - over 52C - that it has had to add a new colour to the top of its scale, a suitably incandescent purple.
Australia's highest recorded temperature is 50.7C, set in January 1960 in South Australia. The record for the hottest average day across the nation was set on Monday, at 40.3C, exceeding a 40-year-old record. "What makes this event quite exceptional is how widespread and intense it's been," said Aaron Coutts-Smith, the weather bureau's climate services manager. "We have been breaking records across all states and territories in Australia over the course of the event so far." Wildfires are raging across New South Wales and Tasmania.
Australia's prime minister Julia Gillard said: "Whilst you would not put any one event down to climate change, weather doesn't work like that, we do know over time that as a result of climate change we are going to see more extreme weather events and conditions."

A fire danger rating sign set to catastrophic sends out a clear message on the situation on the outskirts of Wandandian south of Nowra, near Sydney, New South Wales. Four new ares in NSW have been given a 'catastrophic 'fire danger rating meaning that if fires break out they will be uncontrollable and fast moving, so residents should leave. Photograph: Dean Lewins/EPA

She is right of course to be cautious about attributing individual events to global warming, but it is equally clear that new colours will need to be added to scales across the world for heatwaves and other extreme weather events.
We already know that climate change is loading the weather dice. Scientists have shown that the European heatwave of 2003, that caused over 40,000 premature deaths, was made at least twice as likely by climate change. The Russian heatwave of 2010, that killed 50,000 and wiped out $15bn of crops, was made three times as likely by global warming and led to the warmest European summer for 500 years.
The extreme weather forecast is even worse. Mega-heatwaves like these will become five to 10 times more likely over the next 40 years, occurring at least once a decade, scientists predict.
Work by the most authoritative group of scientists, the UN's Intergovernmental Panel on Climate Change, found that it is 90% certain that heatwaves will increase further in length and severity, as will extreme high tides. It is 66% likely that hurricanes and typhoon winds will get faster and that intense rain will increase, as well as landslides. It is more likely than not that droughts will intensify in Europe, North and Central America and, most dangerously given the poverty there, Southern Africa. There are uncertainties of course, but the basic physics is that heat-trapping carbon emissions mean more energy is being pumped into the system, increasing climate chaos.
The two nations in which the fringe opinions of so-called climate sceptics have been trumpeted most loudly - the US and Australia - have now been hit by record heatwaves and, in the US, superstorm Sandy. The scientists are turning up the volume of their warnings, but whether this leads to loud and clear political action to curb emissions or more shouting from sceptics and the vested fossil fuel interests that support them remains to be seen.

Links

• Australian project simulates effects of runaway climate change
• Deadly heatwaves will be more frequent in coming decades

‘Like Second-Hand Smoke’: Worst Emitters Least Affected By Climate Change

University of Queensland

Industrial emissions.

Global climate change resembles a room of second-hand smoke, new research has found, with countries emitting the least amount of gasses suffering the most.
The study by The University of Queensland and the Wildlife Conservation Society (WCS) shows a dramatic global mismatch, with the highest emitting countries – including Australia - the least vulnerable to climate change effects.
Lead author Glenn Althor, a PhD student in UQ’s School of Geography, Planning and Environmental Management (GPEM) said, in contrast, the countries emitting the least amount of greenhouse gases were the most vulnerable to effects such as increased frequency of natural disasters, changing habitats, human health impacts, and industry stress.
“There is an enormous global inequality in which those countries most responsible for causing climate change are the least vulnerable to its effects,” Mr Althor said.
“It is time that this persistent and worsening climate inequity is resolved, and for the countries with the greatest emissions to act,” he said.
Co-author Associate Professor James Watson of GPEM and WCS said the situation resembled second-hand smoking.
“This is like a non-smoker getting cancer from second-hand smoke, while the heavy smokers continue to puff away,” he said.
“Essentially we are calling for the smokers to pay for the healthcare of the non-smokers they are directly harming.”
The researchers conducted a global analysis of the relationship between a nation’s carbon emissions and vulnerability to climate change.
They found that 20 of the 36 highest emitting countries – including the U.S. Canada, Australia, China, and much of Western Europe – were the least vulnerable to its impacts.
Eleven of the 17 countries with low to moderate emissions were most vulnerable to climate change. Most were found in sub-Saharan Africa and South Asia.
The authors said these countries were not only exposed to serious environmental change such as oceanic inundation or desertification. They were also generally the least developed nations, having few resources available to cope with these issues.
They said the mismatch between the culprits and the affected areas acted as a disincentive for high-emitting “free-rider” countries to mitigate their emissions.
The researchers predicted that the number of acutely vulnerable countries would worsen by 2030 as climate change-related pressures such as droughts, floods, biodiversity loss and disease mounted.
Associate Professor Richard Fuller of UQ’s School of Biological Sciences said the researchers had quantified these inequities using publicly available data.
 “The recent Paris agreement was a significant step forward in global climate negotiations,” he said.
“There now needs to be meaningful mobilisation of these policies, to achieve national emissions reductions while helping the most vulnerable countries adapt to climate change.
“The free rider countries need to do much more to ensure that they bear the burden of coping with climate change impacts.”
The study appears today in the journal Scientific Reports.

Heat To Stay On CSIRO Climate Cuts Amid Claims Malcolm Turnbull Was 'Blindsided'

Fairfax - Peter Hannam

There are claims Malcolm Turnbull was blindsided by the news. Photo: Alex Ellinghausen

Leading scientists will use a national conference on Monday to appeal to the Turnbull government to intervene to reverse plans by the CSIRO to eliminate most of its climate roles amid claims the Prime Minister was "blindsided" by the move.
The cuts, that will cleave about 110 positions from the CSIRO's 140-odd strong Ocean and Atmosphere staff and a similar number from its Land and Water division, were announced in an email from chief executive Larry Marshall on Thursday.
Mr Turnbull and his staff "didn't see it coming", a senior CSIRO researcher has been told. The PM "blanched" when given a copy of the news of the cuts, and asked his staff to investigate, another source tells Fairfax Media.

Stormy times for the CSIRO: On board RV Investigator.

Fairfax Media has sought comment from the PM's office.
Scientists attending Monday's start of the joint national gathering of the Australian Meteorological and Oceanic Society and the ARC Centre of Excellence for Climate System Science in Melbourne are expected to call for a halt to the planned cuts which, including other divisions, will total 350 over two years.
"We strongly believe that the proposed cuts to CSIRO will seriously undermine Australia's capacity to respond to the challenges posed by climate change," the scientists say, according to a copy of the proposed statement obtained by Fairfax Media.

The cuts were announced in an email from CSIRO chief executive Larry Marshall.

Scientists leading the call include David Karoly​ from Melbourne University, Roger Jones from Victoria University and Sarah Perkins-Kirkpatrick from the University of NSW.
"Australia is a continent surrounded by rapidly changing weather patterns, connected to a rapidly changing global climate," the scientists' statement says.
While much has been learnt, there remain many gaps in knowledge, including monitoring changes in the Southern Ocean and how this effects global and regional climate. Another need is to track the changing chemical composition of the atmosphere, including long-term trends based on ice core data, and air quality measurements at Cape Grim in north-west Tasmania, they say.
Senator Richard Di Natale said the Greens plan to use Senate Estimates on Thursday to press Dr Marshall to explain the cuts. The Greens leader also called on the PM to intervene.
"I'd urge the PM to address the situation urgently," Senator Di Natale said. "Our climate science is absolutely critical."
He said Mr Turnbull had inherited a government under Tony Abbott that had attacked climate science, and the PM "has an opportunity to set a different course".
Dr Marshall has said there will be "no net loss" of jobs in two years' time, as other divisions expand. Critics, though, say the dismantling of decades of climate monitoring will be hard to repair and will also undermine the country's ability to participate in international exchanges in climate research.

Links

• CSIRO executives asked to justify deep cuts to climate science
• 'Misleading, inaccurate and in breach of Paris': CSIRO scientist criticises cuts
• Explainer: Why is Tasmania's world heritage area burning?

Explainer: Why Is Tasmania's World Heritage Area Burning?

Fairfax - Adam Morton

The aftermath of fire in the world heritage area on Tasmania's central plateau. Photo: Rob Blakers

What is happening with fire in Tasmania?
The island state is burning in a way it hasn't for many years. Lightning strikes on January 13 sparked a series of blazes, mainly in the state's north-west. It led to the evacuation of coastal hamlets such as Arthur River and the state's famous Overland Track, and threw up smoke that could be seen across the state.
More than three weeks on, and despite some heavy rain that caused flooding in some areas, more than 70 fires are still burning. Most are in the west, where there has been less rain. The fires range from established blazes in remote wilderness to flickering hotspots.

Burned pencil pines near Lake Mackenzie on the central plateau. Photo: Rob Blakers

As of Friday, the Tasmanian Fire service estimated an area of about 105,000 hectares – slightly bigger than greater Melbourne – had been blackened.
More than 20 of the blazes still burning are in the Tasmanian Wilderness World Heritage Area that accounts for roughly a fifth of the state. Others are in or near the cool temperate rainforest of the Tarkine, which is not part of the world heritage area but is the ongoing focus of a campaign by environmentalists for greater protection.

The central plateau before the fire. Photo: Dan Broun

How bad is the damage?
According to scientists familiar with the ecology of the area, bad – and worse when you consider what it suggests what might lie ahead. The destroyed area includes a part of the state's alpine central region, which has historically not burned unless deliberately lit by graziers or campers.
Two photographers, Rob Blakers​ and Dan Broun, hiked to the region in late January and found the fire had destroyed ancient ecosystems of pencil and King Billy pines and large cushion plants that had lived for more than 1000 years.

A cushion plant after the fire. Photo: Rob Blakers

The world heritage area is ecologically diverse and vast, spanning nearly 16,000 square kilometres, with some areas better naturally equipped to recover from fires than others. Best estimates suggest about 15,000 hectares of this have burned this year. Only part of this is on the central plateau.
With fires still burning, it is not yet possible to fully assess the damage. A Tasmanian Fire Service spokeswoman said fire continues to burn near Lake Mackenzie on the central plateau at an altitude of about 1200 metres, near where Blakers and Broun took their pictures. A separate blaze is alight in the Walls of Jerusalem National Park.
Part of the south-west wilderness, some of which is incredibly remote and difficult to reach, is also burning.

A destroyed pencil pine. Photo: Rob Blakers

How long will it take to recover?
It depends on which area we are talking about.
On the central plateau around Lake Mackenzie, the question is whether it will recover at all. The alpine ecosystem there is unique, and a throwback – part of what fire ecologist Professor David Bowman says is a "geological refuge" in western Tasmania that has survived since the time of the supercontinent of Gondwana. While there are ancient ecosystems in other parts of what was once Gondwana that survive in a climate similar to Tasmania's west, none are the same. It does not regenerate after fire in the way a eucalypt forest does. When it is lost, it is likely to be lost for good. If it does recover, it is likely to take more than a millennium.

Fire burns Tasmanian Wilderness World Heritage Area Photo: Rob Blakers

Tasmania's endemic temperate rainforest isn't designed to burn either. It tends to be replaced after fire by eucalypt forest, and can take between 600 and 800 years to return to a more pure rainforest of myrtle beech, leatherwood and sassafras.

Surely this this not the first time these areas have burned?
There have, of course, been fires in the world heritage area before. As recently as January 2013, a blaze near Giblin River in the south-west wilderness beat a path through 45,000 hectares.
In the western alpine region, fires were extremely rare before the arrival of Europeans. Since then there have been a number of fires, lit both accidentally and deliberately, that have significantly reduced what's left of the unique ancient Tasmanian flora. They have slowed since 1982, when the area was declared world heritage and campfires were banned.

Why do these fires have scientists so concerned?
The scale of the fires is enough to spark concern, but it is the conditions under which they started that has experts most worried. The past decade has seen a significant increase in the number of blazes caused by lightning strikes, with the 2013 Giblin River fire an obvious example.
The January 13 lightning storms hit forests that were ready to burn. Western Tasmania had the driest spring on record, and the summer has been hotter than average, with many sites setting new benchmarks. Scientists attribute this to an El Nino in the Pacific Ocean exacerbating the long-term warming trend the planet is experiencing due to the emission of heat-trapping greenhouse gases. They have also warned that climate change will lead to an increase in lightning strikes.
In other words, while there will always be year-to-year variation, these conditions are expected to occur more frequently in future.
Professor Bowman last week told Fairfax Media that he was now deeply concerned about the survival of the state's unique alpine ecosystems. "I think I would be being unethical and unprofessional if I didn't form the diagnosis and say what it is – climate change," he said. "Under the current rate of warming I think this ecosystem will be gone in 50 years."

What can be done?
With fires still burning, the discussion about what, if anything, should be done to improve protection of heritage-listed landscapes has been relatively muted.
Some scientists and environmentalists have expressed concern that authorities – particularly federal agencies that can swing in and help states in times of disaster – are too slow to defend world heritage and other protected areas. They stress the first focus should be saving lives, but argue places of international significance should given as much or more weighting as protecting property that can be rebuilt.
Authorities strenuously deny they have been slow to protect highly valued forests, pointing to more than 30 aircraft dropping water on Tasmania's wilderness, and strike teams that are being sent into forests in a bid to deal with hotspots detected from the air before they burn.
Professor Bowman suggested it may be necessary to start collecting genetic material from threatened ecosystem species to ensure they do not go the way of the thylacine.
All say there will be a proper review once the fires are out. That may be a while yet.

Links

• Click for more photos
• Fire burns Tasmanian Wilderness World Heritage Area

Biomimicry Wave Energy Device Ready To Leave The Nest

CleanTechnica - Tina Casey

A new bio-inspired method of harvesting energy from the ocean has completed its shakedown on land, and now it’s finally ready for its first real test offshore. Called bioWAVE, the wave energy device won’t be venturing too far — Port Fairy in Australia is as far as it’s going — but we can hardly contain our excitement because we’ve been waiting 7 years for this moment.

A Bio-Inspired Wave Energy Device
BioWAVE first crossed CleanTechnica’s radar back in 2008, when we compared the new wave energy concept to kelp.
That might seem a little imaginative considering what the device actually looks like:

However, kelp is pretty much on the money in terms of biomimicry. The BioWAVE wave energy device was inspired by the way that kelp sways and pivots with the movement of ocean swell waves.
The bioWAVE actually gives you a twofer of potential and kinetic wave energy harvesting.
It consists of an array of floats that rise and fall with the up-and-down surface motion of swells, which accounts for the potential energy. The kinetic energy comes in under the surface, as the floats (or “blades”) sway back and forth.
The prototype pictured above is a 250 kilowatt model designed for operation at 30 meters, as a midway step to developing a one-megawatt commercial version for 40–45 meter depths. The eventual goal is to have entire farms of bioWAVE devices — like beds of kelp — linked together.
bioWave 2012 full res fri from Click2it on Vimeo.

 From bioWAVE To Electricity The tricky part is converting all that motion into electricity. The company behind the wave energy device, BioPower Systems (what else?), developed an on-board power conversion system it calls O-Drive.
As illustrated by the schematic at the top of this article, O-Drive is based on a high-pressure hydraulic fluid system, in which fluid is stored in a bank of accumulators. The accumulators literally accumulate the herky-jerky energy of the wave motion and release it in a steady stream to a hydraulic motor. The motor goes to a generator, and the generator cranks electricity into an undersea cable for transmission to the shore.
To pare down maintenance costs, BioPower has designed the O-Drive converter as a detachable module that can be hauled ashore for servicing.
As for inclement weather, when extreme seas threaten to damage the equipment, the bioWAVE floats are  designed to collapse automatically onto the safety of the sea floor.
To get a feel for what’s going to happen when the device is deployed later this year, you can catch the bioWAVE in action on Vimeo.

Whither Wave Energy?
Wave energy is a bit of a risky venture now that offshore wind energy is taking off, but the pursuit is worth it.
One key advantage of wave devices is their relatively low profile above the surface, and in the case of bioWAVE, no profile at all. That provides much more flexibility for site selection than offshore wind turbines, which can easily run into aesthetic obstacles.
In any case, the Australian government has faith. The bioWAVE project is partly supported by the Australian Renewable Energy Agency (ARENA)  and the government of Victoria.
This is a big year for ARENA, which is also behind the unique Perth wave energy project that launched in March.
Here in the US, wave energy is also getting a huge lift from us taxpayers in the form of a public-private shared test bed at Marine Corps Base Hawaii and funding from the Energy Department so group hug.

Links

• Yes, Solar Can Go Lower (Perovskite Solar Cells, That Is)
• US Electric Car Sales Rise 15% (January Electric Car Sales)
• US Renewable Energy Eclipses Fossil Fuels For Second Year Running, Says BNEF
• The Looming Electricity Storage Threat Our Utilities Face
• How 11 Countries Are Leading The Shift To Renewable Energy

The Mystery Of The Expanding Tropics

Nature - Olive Heffernan

As Earth's dry zones shift rapidly polewards, researchers are scrambling to figure out the cause — and consequences.

Severe droughts over the past 20 years in Australia have taken a toll on farmers, who struggle to keep livestock and crops healthy. Amy Toensing/National Geographic Creative

One spring day in 2004, Qiang Fu was poring over atmospheric data collected from satellites when he noticed an unusual and seemingly inexplicable pattern. In two belts on either side of the equator, the lower atmosphere was warming more than anywhere else on Earth. Fu, an atmospheric scientist at the University of Washington in Seattle, was puzzled.
It wasn't until a year later that he realized what he had discovered: evidence of a rapid expansion of the tropics, the region that encircles Earth's waist like a green belt. The heart of the tropics is lush, but the northern and southern edges are dry. And these parched borders are growing — expanding into the subtropics and pushing them towards the poles.
Cities that currently sit just outside the tropics could soon be smack in the middle of the dry tropical edge. That's bad news for places like San Diego, California. "A shift of just one degree of latitude in southern California — that's enough to have a huge impact on those communities in terms of how much rain they will get," explains climate modeller Thomas Reichler of the University of Utah in Salt Lake City.
Since Fu and his colleagues announced their discovery¹ in 2006, many scientists have investigated the tropical bloating and tried to decipher its cause. Explanations range from global warming to ozone depletion or natural cycles that will reverse in the future. And there is little agreement on how quickly the border of the tropics is shifting: estimates run from less than half a degree of latitude per decade to several. At the more extreme end, the change in climate would be like moving London to the position of Rome over the course of a century², ³, ⁴, ⁵. The problem is compounded by lack of consensus on how to define the tropics, which makes it hard for scientists to agree on the extent of the changes. Nevertheless, researchers investigating this phenomenon agree that it is real.
"There's a big need to be concerned about this issue," says climate scientist Chris Lucas at the Australian Bureau of Meteorology in Melbourne. That's because of the possible impacts: some of the world's most fertile fishing grounds could disappear, global grain production could shrink and biodiversity could suffer.

Strange skies
At the same time as Fu first discovered odd patterns in the satellite data, Reichler noticed something unusual in the skies. He was researching the tropopause, the boundary between the lowest level of the atmosphere (the troposphere) and the layer above it (the stratosphere). At the Equator, the tropopause is normally several kilometres higher than at the poles, because warm air rises and pushes the boundary upwards. While analysing temperature data collected from weather balloons, Reichler had found that this equatorial bulge in the tropopause was expanding towards the poles, a sign that the tropics were growing. Fu heard about Reichler's data, and they decided to publish their discoveries together¹.
Ten years after they sounded the alarm, scientists are still struggling to work out what is happening. Last July, 50 researchers gathered in Santa Fe, New Mexico, to discuss everything that is known about tropical expansion — how to measure it, what is causing it and where the future border of the tropics might be. "We're at a stage where we recognize the problem is more complex than we originally thought," explains the organizer of the conference, Dian Seidel, an atmospheric scientist with the US National Oceanic and Atmospheric Administration (NOAA) in Silver Spring, Maryland.
Some of the changes in the tropics could be a result of global warming. Reichler investigated that possibility in a study⁶ led by Jian Lu, an Earth systems scientist now at the Pacific Northwest National Laboratory in Richland, Washington. Working with Gabriel Vecchi, a climate scientist with NOAA in Princeton, New Jersey, the researchers looked at climate forecasts to see how warming might affect an atmospheric circulation pattern called the Hadley cell, which transports heat from the warmer parts of Earth towards the cooler regions (see 'Bulging waistline'). As part of the Hadley cell, warm, moist air soars skywards above the Equator and cool, dry air tumbles towards Earth at about 30° latitude in the Northern and Southern Hemispheres. That downward limb of the Hadley cell helps to create some of the driest deserts on the planet, such as the Kalahari in southern Africa and the Sahara in northern Africa, and it is one of the most common measures of the boundary between the tropics and the drier subtropics. 

In their study, Lu and his colleagues found that climate models generally forecast that the outer edge of the Hadley cell will shift because of global warming. But the models predict a much slower rate of tropical expansion than has been seen so far — which has led researchers to suspect that something else is going on.
 A common view, and one held by Lucas, is that natural climatic variability is playing some part. That variability could take the form of large-scale climatic cycles such as the Pacific Decadal Oscillation, in which temperatures in the Pacific Ocean swing between hot and cold across timescales of 15–20 years or more. "Or it could be in the form of much more random, chaotic noise," says Lucas, who thinks that large cycles and noise together account for 50% or more of the expansion. Atmospheric scientist Darryn Waugh at Johns Hopkins University in Baltimore, Maryland, agrees. "It's a chaotic system, so some of the variability is just noise in the system." If that is the case, tropical expansion could slow down or even reverse in some regions when those natural variations swing back.

Another answer might involve different forces in the Northern and Southern hemispheres. South of the Equator, tropical expansion has been strongest in the summer, and that leads some researchers to suspect that it is related to the pattern of ozone loss in the southern stratosphere. Pollutants chew up ozone molecules above Antarctica in the spring, which triggers circulation changes throughout other parts of the Southern Hemisphere during summer. The correlation with tropical expansion suggests that the two phenomena could be connected. What's more, climate models that factor in ozone loss are able to account for much more of the tropical expansion between 1980 and 2000, when the Antarctic ozone hole was growing bigger nearly every year, says Waugh⁷.

In the Northern Hemisphere, a different explanation is called for because, in general, the Arctic does not suffer the same sort of ozone loss as the Antarctic. Research led by climate scientist Bob Allen at the University of California, Riverside, suggests that the culprits in the north might be black soot and tropospheric ozone — which are both generated by burning fossil fuels. Allen and his team ran simulations with a climate model that featured detailed atmospheric physics, and their analysis showed that black soot and tropospheric ozone have heated the atmosphere in the Northern Hemisphere and driven tropical expansion more than carbon dioxide and other greenhouse gases, particularly in summer⁸.

"The change in climate would be like moving London to the position of Rome over the course of a century."

Not everyone is comfortable with the idea that entirely separate factors could drive tropical expansion to such a large extent on either side of the Equator. Fu, for one, thinks it's unlikely given the similar patterns in the north and south. "If ozone depletion was dominating the expansion in the Southern Hemisphere in the past 30 years, would you see such symmetry? I'm not convinced," says Fu.

The proliferation of hypotheses shows how much researchers are struggling to explain what's happening. "I think we're piecing this together slowly," says Lucas. "We don't have a full explanation yet and I don't think there's going to be one single explanation. It's going to be a little bit of this and a little bit of that."

Edge effect

Right around the time that scientists were first warning about tropical expansion, Lucas was experiencing what might have been its effects first-hand. During 2006 and 2007, Australia was deep in the middle of one of the worst droughts to have hit the continent since Europeans settled there. Lucas recalls driving from Melbourne to nearby Lake Eildon and seeing the once-brimming lake empty. Meanwhile, Melbourne's reservoirs were running low, and north of the city, forest fires raged in the mountains. The worst-affected regions of Australia — cities such as Perth, Adelaide and Melbourne — were south of 30° latitude, which suggests that the drying could be caused by a shift in the position of the Hadley cell and the rain-bearing jet stream. According to research published⁹ in 2010, southeastern Australia has been invaded by a drier climate from the north in recent decades, which has greatly reduced rainfall. "We can't say that this is exclusively due to tropical expansion, but it's certainly consistent with tropical expansion," explains Lucas. "And our concern is that southeastern Australia is going to keep getting drier."

Elsewhere, there is evidence that tropical expansion is affecting the ocean. Where the Hadley cell descends, bringing cool air downward, it energizes the ocean and whips up currents to high speeds. This energy powers the upwelling of cold, nutrient-rich waters towards the surface, which feeds some of the world's most productive fisheries. But there are hints that some of these regions are suffering because of shifts in the Hadley cell.

Edward Vizy and Kerry Cook¹⁰, both at the University of Texas at Austin, have found some unhealthy signs in the region of the Benguela Current, an area of coastal upwelling along the coast of west Africa and south of 30° latitude. According to Cook, the currents of that entire region have shifted over the past 30 years. One effect is that the upwelling has weakened, with worrying implications for the region's fisheries and biodiversity. Cook says that the same could be true of open-ocean upwelling systems, which are more susceptible to changes in the position of the Hadley cell.

These upwelling zones could move south over time, or get weaker or stronger, depending on what happens to the Hadley cell, says Cook. In any case, it means that fishing communities that rely on these resources will not be able to count on traditional patterns.

On land, biodiversity is also potentially at risk. This is especially true for the climate zones just below the subtropics in South Africa and Australia, on the southern rim of both continents. In southwestern Australia, renowned as one of the world's biodiversity hotspots, flowers bloom during September, when tourists come to marvel at some of the region's 4,000 endemic plant species. But since the late 1970s, rainfall there has dropped by one-quarter. The same is true at South Africa's Cape Floristic Province, another frontier known for its floral beauty. "This is the most concrete evidence we have of tropical expansion," says Steve Turton, an environmental geographer at James Cook University in Cairns, Australia.

Turton worries that the rate of change will be too rapid for these ecosystems to adapt. "We're talking about rapid expansion that's within half or a third of a human lifetime," he says. In the worst-case scenario, the subtropics will overtake these ecologically rich outposts and the hotter, drier conditions will take a major toll.

For the scientists working in this field, communicating the threat of tropical expansion will be tricky, given the level of uncertainty. "It's frustrating to see how much work we have left," says Thomas Birner, an atmospheric scientist at Colorado State University in Fort Collins and one of the conveners of the Santa Fe meeting. One outcome of that conference was an agreement that scientists should compare the various metrics for measuring tropical expansion in the hope of agreeing on the best way forward.

More time will also help. If tropical expansion continues at a fairly constant rate, says Waugh, there will be less of a chance that natural variability is the main culprit, and the finger will point more strongly to other causes.

But that long wait for an answer will be no comfort for the residents of cities such as Santiago, San Diego and Melbourne, and for the billions of others who live near the boundary between the tropics and subtropics. "We need to understand this issue," says Lucas, "to have a sustainable civilization there."

Links

• Tropical forest losses outpace UN estimates
• The case of the missing heat
• The fragile framework
• Hunting the Godzilla El Niño
• Quest for climate-proof farms
• Battle for the Amazon
• Life ­– a status report