13/11/2019

Scientists looked at sea levels 125,000 years in the past. The results are terrifying

The Conversation -  |  | 

A polar bear wandering on melting pack ice in Canada, north of the Arctic Circle, during the summer 2017. Scientists say the last interglacial offers lessons for future sea level rise. Florian Ledoux/The Nature Conservancy
Sea levels rose 10 metres above present levels during Earth’s last warm period 125,000 years ago, according to new research that offers a glimpse of what may happen under our current climate change trajectory.
Our paper, published today in Nature Communications, shows that melting ice from Antarctica was the main driver of sea level rise in the last interglacial period, which lasted about 10,000 years.
Rising sea levels are one of the biggest challenges to humanity posed by climate change, and sound predictions are crucial if we are to adapt.
This research shows that Antarctica, long thought to be the “sleeping giant” of sea level rise, is actually a key player. Its ice sheets can change quickly, and in ways that could have huge implications for coastal communities and infrastructure in future.
Aerial footage showing devastation caused by severe storms at Collaroy on Sydney’s northern beaches in June 2016. UNSW Water Research Laboratory
A warning from the past
Earth’s cycles consist of both cold glacial periods - or ice ages - when large parts of the world are covered in large ice sheets, and warmer interglacial periods when the ice thaws and sea levels rise.
The Earth is presently in an interglacial period which began about 10,000 years ago. But greenhouse gas emissions over the past 200 years have caused climate changes that are faster and more extreme than experienced during the last interglacial. This means past rates of sea level rise provide only low-end predictions of what might happen in future.
We examined data from the last interglacial, which occurred 125,000 to 118,000 years ago. Temperatures were up to 1℃ higher than today - similar to those projected for the near future
Our research reveals that ice melt in the last interglacial period caused global seas to rise about 10 metres above the present level. The ice melted first in Antarctica, then a few thousand years later in Greenland.
Sea levels rose at up to 3 metres per century, far exceeding the roughly 0.3-metre rise observed over the past 150 years.
The early ice loss in Antarctica occurred when the Southern Ocean warmed at the start of the interglacial. This meltwater changed the way Earth’s oceans circulated, which caused warming in the northern polar region and triggered ice melt in Greenland.
Dogs hauling a sled through meltwater on coastal sea ice during an expedition in northwest Greenland,June 2019. STEFFEN M. OLSEN/DANISH METEOROLOGICAL INSTITUTE
Understanding the data
Global average sea level is currently estimated to be rising at more than 3 millimetres a year. This rate is projected to increase and total sea-level rise by 2100 (relative to 2000) is projected to reach 70-100 centimetres, depending on which greenhouse gas emissions pathway we follow.
Such projections usually rely on records gathered this century from tide gauges, and since the 1990s from satellite data.
Most of these projections do not account for a key natural process - ice-cliff instability - which is not observed in the short instrumental record. This is why geological observations are vital.
When ice reaches the ocean, it becomes a floating ice-shelf which ends in an ice-cliff. When these cliffs get very large, they become unstable and can rapidly collapse.
This collapse increases the discharge of land ice into the ocean. The end result is global sea-level rise. A few models have attempted to include ice-cliff instability, but the results are contentious. Outputs from these models do, however, predict rates of sea-level rise that are intriguingly similar to our newly observed last interglacial data.
Antactica was long thought to be the sleeping giant of sea level rise, but is now considered a key driver. Australian Antarctic Division
Our work examines records of total sea-level change, which by definition includes all relevant natural processes.
We examined chemical changes in fossil plankton shells in marine sediments from the Red Sea, which reliably relate to changes in sea level. Together with evidence of meltwater input around Antarctica and Greenland, this record reveals how rapidly sea level rose, and distinguishes between different ice sheet contributions.

Looking to the future
What is striking about the last interglacial record is how high and quickly sea level rose above present levels. Temperatures during the last interglacial were similar to those projected for the near future, which means melting polar ice sheets will likely affect future sea levels far more dramatically than anticipated to date.
The last interglacial is not a perfect scenario for the future. Incoming solar radiation was higher than today because of differences in Earth’s position relative to the Sun. Carbon dioxide levels were only 280 parts per million, compared with more than 410 parts per million today.
Crucially, warming between the two poles in the last interglacial did not happen simultaneously. But under today’s greenhouse-gas-driven climate change, warming and ice loss are happening in both regions at the same time. This means that if climate change continues unabated, Earth’s past dramatic sea level rise could be a small taste of what’s to come.

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(AU) Drought And Climate Change Were The Kindling, And Now The East Coast Is Ablaze

The Conversation -  | 

Multiple large, intense fires are stretching from Australia’s coast to the tablelands and parts of the interior. AAP Image/Supplied, JPSS | LARGE IMAGE
Last week saw an unprecedented outbreak of large, intense fires stretching from the mid-north coast of New South Wales into central Queensland.
The most tragic losses are concentrated in northern NSW, where 970,000 hectares have been burned, three people have died, and at least 150 homes have been destroyed.
A catastrophic fire warning for Tuesday has been issued for the Greater Sydney, Greater Hunter, Shoalhaven and Illawarra areas. It is the first time Sydney has received a catastrophic rating since the rating system was developed in 2009.
No relief is in sight from this extremely hot, dry and windy weather, and the extraordinary magnitude of these fires is likely to increase in the coming week. Alarmingly, as Australians increasingly seek a sea-change or tree-change, more people are living in the path of these destructive fires.

 Unprecedented state of emergency
Large fires have happened before in northern NSW and southern Queensland during spring and early summer (for example in 1994, 1997, 2000, 2002, and 2018 in northern NSW). But this latest extraordinary situation raises many questions.
It is as if many of the major fires in the past are now being rerun concurrently. What is unprecedented is the size and number of fires rather than the seasonal timing.
The potential for large, intense fires is determined by four fundamental ingredients: a continuous expanse of fuel; extensive and continuous dryness of that fuel; weather conditions conducive to the rapid spread of fire; and ignitions, either human or lightning. These act as a set of switches, in series: all must be “on” for major fires to occur.
Live fuel moisture content in late October 2019. The ‘dry’ and ‘transitional’ moisture categories correspond to conditions associated with over 95% of historical area burned by bushfire. Estimated from MODIS satellite imagery for the Sydney basin Bioregion.
The NSW north coast and tablelands, along with much of the southern coastal regions of Queensland are famous for their diverse range of eucalypt forest, heathlands and rainforests, which flourish in the warm temperate to subtropical climate.
These forests and shrublands can rapidly accumulate bushfire fuels such as leaf litter, twigs and grasses. The unprecedented drought across much of Australia has created exceptional dryness, including high-altitude areas and places like gullies, water courses, swamps and steep south-facing slopes that are normally too wet to burn.
These typically wet parts of the landscape have literally evaporated, allowing fire to spread unimpeded. The drought has been particularly acute in northern NSW where record low rainfall has led to widespread defoliation and tree death. It is no coincidence current fires correspond directly with hotspots of record low rainfall and above-average temperatures.
Annual trends in live fuel moisture. The horizontal line represents the threshold for the critical ‘dry’ fuel category, which corresponds to the historical occurrence of most major wildfires in the Bioregion. Estimated from MODIS imagery for the Sydney basin Bioregion
Thus, the North Coast and northern ranges of NSW as well as much of southern and central Queensland have been primed for major fires. A continuous swathe of critically dry fuels across these diverse landscapes existed well before last week, as shown by damaging fires in September and October.
High temperatures and wind speeds, low humidity, and a wave of new ignitions on top of pre-existing fires has created an unprecedented situation of multiple large, intense fires stretching from the coast to the tablelands and parts of the interior.

More people in harm’s way
Many parts of the NSW north coast, southern Queensland and adjacent hinterlands have seen population growth around major towns and cities, as people look for pleasant coastal and rural homes away from the capital cities.
The extraordinary number and ferocity of these fires, plus the increased exposure of people and property, have contributed to the tragic results of the past few days.
Communities flanked by forests along the coast and ranges are highly vulnerable because of the way fires spread under the influence of strong westerly winds. Coastal communities wedged between highly flammable forests and heathlands and the sea, are particularly at risk.
As a full picture of the extent and location of losses and damage becomes available, we will see the extent to which planning, building regulations, and fire preparation has mitigated losses and damage.
A firefighter defends a property in Torrington, near Glen Innes, Sunday, November 10, 2019. There are more than 80 fires burning around the state, with about half of those uncontained. AAP Image/Dan Peled
These unprecedented fires are an indication that a much-feared future under climate change may have arrived earlier than predicted. The week ahead will present high-stakes new challenges.
The most heavily populated region of the nation is now at critically dry levels of fuel moisture, below those at the time of the disastrous Christmas fires of 2001 and 2013. Climate change has been predicted to strongly increase the chance of large fires across this region. The conditions for Tuesday are a real and more extreme manifestation of these longstanding predictions.
Whatever the successes and failures in this crisis, it is likely that we will have to rethink the way we plan and prepare for wildfires in a hotter, drier and more flammable world.

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(AU) 'Old Hat': Is There A Link Between Climate Change And Bushfires?

Sydney Morning Herald - Peter Hannam

As Sydney braces for its first ever day of catastrophic fire danger, it's worth recapping what scientists think about the links between bushfire risks and a warming world.
Is there a link between climate change and more severe and frequent bushfires?
The aftermath of fire in Rainbow Flat near the Pacific Highway on November 9. Credit: Dean Sewell



 How do scientists measure fire danger?
The likelihood of hostile extreme weather can be measured in a range of ways. For bushfires, scientists look at the McArthur Forest Fire Danger Index, developed in the 1960s by CSIRO scientist A.G. McArthur to forecast how weather would affect fire behaviour.
As the name suggests, the gauge examines the risks to woodlands from fire using a combination of rainfall or drought conditions along with predicted wind speeds, temperature and relative humidity.
Typically, winter and spring see the highest ratings on this fire danger index in the north and these move southwards as spring makes way for summer.

How bad is catastrophic then?
Fire and emergency authorities started to review response plans in 2008 to adjust to "the growing intensity and severity of recent bushfire experiences across the country".
Then Black Saturday's bushfires erupted in Victoria on February 7 in 2009, leaving 173 people dead. That event "brought into sharp focus the possibility that the current legislation, systems, practices and processes to support effective community safety outcomes may no longer match the increasing levels of risk and expectations", a bushfire warning taskforce report noted.
The highest fire danger rating was set as "catastrophic" for index readings of 100 or more. (In Victoria, they are dubbed Code Red.) The basic message was boiled down to: "For your survival, leaving is the best option."
The dire assessment is because some fires on such days are likely to become "uncontrollable, unpredictable and fast moving" and "there is a very high likelihood that people in the path of the fire will die or be injured", the taskforce said.
Melbourne reached an index reading of about 150 on Black Saturday, according to Ross Bradstock, director of the Centre for Environmental Risk Management of Bushfires at the University of Wollongong. For Sydney to exceed 100 on the index could be a first, at least for its Observatory Hill and Sydney Airport sites, where the weather is measured.

Does climate change play a part?
Yes, there is a link between climate change and the prevalence and severity of fires. In fact, the research identifying a link between fires and climate change is "old hat", says Professor Bradstock. "The research has all been done. We don’t need to keep doing it."
As the Bureau of Meteorology and CSIRO pointed out in last year's latest State of the Climate report, the number of the most extreme 10 per cent of fire weather days based on the fire danger index "has increased in recent decades across many regions of Australia, especially in southern and eastern Australia".
How fire danger risks are rising in Australia
Source: Bureau of Meteorology, CSIRO

"There has been an associated increase in the length of the fire weather season," it said. "Climate change, including increasing temperatures, is contributing to these changes."
Or, as Hamish Clarke, a former NSW government scientist and now with the University of Wollongong, puts it: "Across the country, at a number of high-quality long-term weather stations, there had either been an increase, or no change [in the fire danger index]. We didn’t find a significant decrease anywhere."
In general, one consequence for fire authorities is that the fire season is getting longer. In eastern Australia, that means fire risks start to increase earlier in the spring and last longer into the autumn. The window for hazard-reduction burning is shifting into winter – if it's not too damp to do it.
How human activity and natural climate variability factored in bushfire ratings increases from 1973 to 2017 was the focus of research by Sarah Harris, from the Victoria's Country Fire Authority, and Chris Lucas in September.
Firefighters north of Forster near the junction of the Pacific Highway on November 8. Credit: Dean Sewell
While rainfall changes from one year to the next, with phenomena such as El Ninos in the Pacific and shifting Indian Ocean conditions playing a role, the researchers' findings were conclusive:
"We propose that anthropogenic [human-led] climate change is the primary driver of the [upward trend in the fire danger index], through both higher mean temperatures and, potentially, through associated shifts in large-scale rainfall patterns."

How unusual is this year?
Depending on where you are, very unusual. NSW, for instance, could see a million hectares burned so far this fire season within days – if it hasn't already done so. That is about the same as the past three fire seasons combined – and summer is yet to arrive.
Rainfall deficiencies – or what most of us call "drought" – are already the worst on record for northern NSW and parts of southern Queensland. And it has also been hot.

Fires will take off when forests are as dry as this
Median live fuel moisture content, Sydney Basin
2013 saw Sydney's last major fires.

Source: R.H.Nolan, M.M. Boer and R.A. Bradstock
According to the Bureau of Meteorology, Australia posted its hottest January-October in records going back to 1910 for maximum temperatures. It looks like only a cool spell, which is not on the forecast charts, will stop 2019 being the hottest year on record for daytime readings.
Of particular concern for this week is how very dry areas are around big population centres such as Sydney, Newcastle and Wollongong.
Temperatures are likely to reach the mid- to high 30s on November 12 at a time when moisture levels in plants – a gauge of how quickly they will burn if fire breaks out – are tracking below those of the big fire season of 2013 in the Sydney area, and the worst since 2002.
Professor Bradstock published research in 2009 that predicted how the fire danger index would track to 2030 and 2050, using CSIRO data from 2007.
"The current predictions [for Sydney on November 12] are beyond what we predicted back in 2007," he says. "That's not good."
The Hillville fire on November 8. Credit: Dean Sewell 
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