27/07/2019

Recent Warming ‘Unmatched In The Past 2000 Years’

Cosmos - Richard A Lovett

Events are happening globally and simultaneously, research shows.
Modern climate change is starkly different because more than 98% of the Earth is warming simultaneously, research shows. AUSCAPE / GETTY IMAGES
Climate-change sceptics sometimes argue that there is no cause for concern from global warming because in the past 2000 years the world has already gone through several natural cycles of warming and cooling from which it has always rebounded on its own.
However, new research has found that rather than being global events, these natural cycles were actually regional changes that never affected more than part of the globe at any one time.
Furthermore, these warming and cooling patterns didn’t occur anywhere close to simultaneously in the parts of the world they did affect.
The findings are published in a suite of papers in the journals Nature and Nature Geoscience.
“Traditionally, the understanding is that there were globally coherent periods of climate variability,” says Nathan Steiger, a paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory in New York, US, who was part of a study team led by Raphael Neukom, a climate researcher from the University of Bern, Switzerland.
“There was a cold period called the Little Ice Age [1300-1850 AD], a warm period called the Medieval Warm Period [800-1200 AD], and a couple of other periods as we go back further in time [the Dark Ages Cold Period, 400-800 AD, and the Roman Warm Period, 1-400 AD].
“But what we show is that these periods weren’t globally coherent, as previously thought.”
Modern climate change, on the other hand, is starkly different, not just because of the rapid rate of warming, but because more than 98% of the Earth is warming simultaneously.
“That very much stands out in contrast to the past 2000 years,” Steiger says.
The reason this wasn’t discovered before appears to be that these multi-century warming and cooling epochs were best documented in Europe. So much so, that most of their names are tied to European history: Medieval Warming, Dark Ages Cooling, Roman Warming.
“It was easy to make the assumption that these changes were happening everywhere on the planet at the same time,” says Scott St. George, a paleoclimatologist at the University of Minnesota, US, who was not part of the study team, but wrote a supporting commentary in Nature.
“What this study has demonstrated is that less than half of the planet was being pushed in the same direction – whether warming or cooling – at the same time.”
Now, he says, “no matter where you go, everywhere is being pushed in the same direction at the same time”.
To prove this, Steiger, Neukom and colleagues turned to a newly created global database of climate records called PAGES 2k, which compiled nearly 700 measures of climate over the past 2000 years, based on such measures as tree rings, ice cores, growth patterns in coral reefs, cave deposits, and sediment records, from across the world.
From this, for example, they discovered that the coldest parts of the Little Ice Age hit the central and eastern Pacific in the fifteenth century, but didn’t hit major parts of Europe or North America until the seventeenth century – and were delayed in other parts of the world until the nineteenth.
Not that this means natural processes can’t produce simultaneous climate shifts.
But, unlike the multi-century shifts, these occur over time horizons of a decade or two, says Neukom, who led a separate study that used the same PAGES 2k dataset to look at shorter-term shifts in global climate.
What they found, Neukom says, is that in pre-industrial times these shifts were driven primarily by major volcanic eruptions, which blasted fine particles high into the atmosphere, producing a bright haze that reflects sunlight back into space, reducing the amount of heat reaching the Earth’s surface.
In yet another study, a team led by Stefan Brönnimann, also of the University of Bern, concluded that many of the impacts of even the Little Ice Age are the result of volcanic activity – specifically a cluster of five major eruptions that occurred between 1808 and 1835.
The most famous of these is the 1815 eruption of Indonesia’s Mt. Tambora – one of the most massive volcanic blasts in human history, and cause of what later became known in major parts of the Northern Hemisphere as “The Year Without a Summer”.
These blasts, Brönnimann, says, produced a “gear shift” in many parts of the world’s climate systems, producing, among other things, weak monsoons in Africa and India, and changes in ocean circulation that produced climate effects that reverberated all the way through the 1840s.
Among other things, these caused a southward shift in North Atlantic storms that dumped more snow in the Alps and contributed to advance of their glaciers, years after the last of the eruptions.
St. George adds that it’s also been suggested that the Medieval Warm Period might, in large part, have been created by a “long, quiet period” without major volcanic eruptions. “It sounds plausible,” he says.
As for the cause of the current warming period?
“We didn’t address the question of human causes,” Steiger says. “It’s implied, rather than explicit. There’s a lot of evidence that the contemporary period is human-caused. We don’t have to look at paleoclimate to look at that.”

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2,000 Years Of Records Show It’s Getting Hotter, Faster

The Conversation - 

European heatwaves are part of a pattern of rapid global warming. EPA/ABEL ALONSO
New reconstructions of Earth’s temperature over the past 2,000 years, published today in Nature Geoscience, highlight the astonishing rate of the recent widespread warming of our planet.
We also now have a clearer picture of decade-to-decade temperature variations, and what drove those fluctuations before the industrial revolution took hold.
Contrary to previous theories that pre-industrial temperature changes in the last 2,000 years were due to variations in the Sun, our research found volcanoes were largely responsible. However, these effects are now dwarfed by modern, human-driven climate change.

 Reading the tree rings
Without networks of thermometers, ocean buoys and satellites to record temperature, we need other methods to reconstruct past climates. Luckily, nature has written the answers down for us. We just have to learn how to read them.
Corals, ice cores, tree rings, lake sediments, and ocean sediment cores provide a wealth of information about past conditions – this is called “proxy” data – and can be brought together to tell us about the global climate in the past.

Tree rings, corals and ice cores all provide ‘proxy data’ – information about changing temperatures over the centuries. Simon Stankowski/Unsplash, CC BY
Teams of scientists around the world have spent many thousands of hours of field and laboratory work to collect and analyse samples, and ultimately publish and make available their data so other scientists can undertake further analysis. 
Previously, our team, along with many other proxy experts, meticulously analysed and collated temperature-sensitive proxy data covering the last 2,000 years from around the world, creating the largest database of temperature-sensitive proxy data yet assembled. We then made all of the data publicly available in one place.

Astonishing consistency between reconstruction methods
With this unique dataset in hand, our team set about reconstructing past global temperature.
We scientists are notoriously sceptical of our own analysis. But what makes us more confident about our findings is when different methods applied to the same data yield the same result.
In this paper we applied seven different methods to reconstruct global temperature from our proxy network.
We were astounded to find that the methods all gave remarkably similar results for multidecadal fluctuations – a very precise result considering the breadth of the methods used.
This gave us the confidence to delve further into what drove global temperature fluctuations on decadal timescales before the industrial revolution really took hold.

What happened before human-induced climate change?
Our study produces the clearest picture yet of Earth’s average temperature over the past two millennia. We also found that climate models performed very well in comparison, and they succeed in capturing the amount of natural variability in the climate system - the natural ups and downs in temperature from year-to-year and decade-to-decade.
Using climate models and reconstructions of external climate forcing, such as from volcanic eruptions and solar variability, we deduced that before the industrial revolution, global temperature fluctuations from decade to decade in the past 2,000 years were mainly controlled by aerosol forcing from major volcanic eruptions, not variations in the Sun’s output. Volcanic aerosols have a temporary cooling effect on the global climate.
Following these temporary cooling periods our reconstructions show there is an increased probability of a temporary warming period due to the recovery from volcanic cooling.


Earlier this year One Nation leader Pauline Hanson suggested that volcanic eruptions may be responsible for the recent rise in atmospheric carbon dioxide levels.

Recent warming is far beyond natural variability
There are, of course, natural changes in Earth’s temperature from decade to decade, from century to century, and also on much longer timescales. With our new reconstructions were also able to quantify the rate of warming and cooling over the past 2,000 years.
Comparing our reconstructions to recent worldwide instrumental data, we found that at no time in the last 2,000 years has the rate of warming been so high.
In statistical terms, rates of warming during all 51-year periods from the 1950s onwards exceed the 99th percentile of reconstructed pre-industrial 51 yr trends. If we look at timescales longer than 20 years, the probability that the largest warming trend occurred after 1850 greatly exceeds the values expected from chance alone. And, for trend lengths over 50 years, that probability swiftly approaches 100%.
 So what do all these stats mean? The strength of the recent warming is extraordinary. It is yet more evidence of human-induced warming of the planet.

But hasn’t there been natural climate change in the past?
Our understanding of past temperature variations of the Earth contributes to understanding such fundamental things as how life evolved, where our species came from, how our planet works and, now that humans have fundamentally altered it, how modern climate change will unfold.
We know that over millions of years, the movement of tectonic plates and interactions between the solid earth, the atmosphere and the ocean, have a slow effect on global temperature. On shorter (but still very long) timescales of tens to hundreds of thousands of years, our planet’s climate is gradually influenced by small variations in the geometry of the Earth and the Sun, for example, small wobbles and variations in the Earth’s tilt and orbit.
From the Last Glacial Maximum, about 26,000 years ago, when huge ice sheets covered large parts of the Northern Hemisphere landmass, Earth transitioned to a 12,000-year warm period, called the Holocene.
This was a time of relative stability in global temperature, apart from the temporary cooling effect of the odd volcano. With the development of human agriculture, our prosperity and population grew. Before the industrial revolution, Earth had not seen carbon dioxide concentrations above current levels for at least 2 million years.

Following the industrial revolution, warming commenced due to human activity. With a clearer picture of temperature variations over the past two millennia we now have a better understanding of the extraordinary nature of recent warming.
It is up to all of us to decide whether this is the kind of experiment we want to run on our planet.

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Barwon-Darling River Faces 'Collapse' From Government Mistakes: Report

Sydney Morning Herald - Peter Hannam

Immediate changes are needed to avoid the "collapse" of Australia's longest river system, with a government agency finding over-extraction brought forward drought conditions for parts of the river by three years.
In a highly critical draft review of the 2012 water sharing plan for the Barwon-Darling, released on Wednesday, the NSW Natural Resources Commission found the riverine ecosystem to be "in crisis".
Some aquatic species "will take decades to recover, if they recover at all", it said, blaming in part changes that allowed irrigators greater extraction rights. Cotton alone used about 1 trillion litres in the five years to 2015-16.
The longest river system in Australia is on course for "collapse", the NSW's Natural Resources Commissioner warns in a new report. Credit: Janie Barrett
"There is clear evidence to indicate that the [water-sharing] plan rules are resulting in more frequent and longer cease-to-flow periods," said the report, which covers an area from Mungindi on the Queensland border to just south of Wilcannia in far-western NSW.\"There is an urgent need to remake the plan so the current trend of a river system heading towards collapse is reset, and the river and its dependent species, communities and industries are put on a path towards long term health and resilience," commissioner John Keniry said in a statement.
The commission makes 17 recommendations aimed at promoting three stages of reform. The first priority, though, should be for "an open, evidence based, and independently peer reviewed process to develop a new plan".
The report comes at a time when most of NSW and other parts of the Murray-Darling Basin are facing an intensification of drought with little immediate relief predicted in coming months at least.
Many towns are facing tight water restrictions, important wetlands are drying out and many farmers are facing limited, if any, water allocations for the current year. Residents of Menindee on the lower Darling fear a return of mass fish kills this summer.

'Scathing' report
Several mass fish kills in the Darling River at Menindee illustrated the plight of the river during the past summer. Credit: Nick Moir
The Berejiklian government should make "immediate" changes to the plan by next year "to rebuild social licence for water management in local communities" as the first stage of suggested changes, the report says.
The NSW Department of Planning, Industry and Environment should then remake the plan by July 1, 2023, when the current one expires, and it should also review upstream water sharing plans that affect the Barwon-Darling, it said.
Kate Smolski, chief executive of the NSW Nature Conservation Council, said it was a "scathing report which places the blame for the ecological catastrophe we have seen unfold in the Darling squarely at the feet of the NSW government for allowing over extraction by upstream irrigators".
"The report also highlights the devastating effect that climate change will have on water availability in the catchment," Ms Smolski said. "It is clear that a comprehensive review of climate change impacts on water availability across the entire Murray-Darling Basin is needed."
A commission spokesman said climate change "was not effectively addressed" in the 2012 plan.
"Latest CSIRO best estimates of climate change show that while rainfall predictions are highly uncertain temperatures will increase and evaporation rates will increase," he said.
"In-flows to the Barwon-Darling are likely to decline in the future, resulting in a 10 per cent reduction in end-of-system flows by 2030."
A cotton farm near Bourke on the Barwon-Darling in north-west NSW endures dry times. Credit: Kate Geraghty
'Near-criminal'
Jodi McKay, NSW Labor leader, told reporters the handling of the Barwon-Darling was "near-criminal", and said the report was a "significant indictment of the management of water by the National Party in this state".
"We've always said National Party ministers shouldn't be in charge of water", Ms McKay said.
A spokeswoman for Melinda Pavey, the water minister, said the government would review the draft and respond to its recommendations when the report is finalised in September.
"The government has embarked on significant water reform over the past 12 months as was recognised by the NRC in the report," she said.
‘Water is critical to everyone in our western NSW communities and their feedback on the draft report will be integral to how we respond to the recommendations."
Ms Pavey's predecessor, Niall Blair, said "at no time during my time as water minister, did I shy away from the hard decisions".
He cited his move to bring forward the review of the plan by several years, the greater protection of environmental water, and the establishment of the Natural Resources Access Regulator as examples of those measures.
Roy Butler, the Shooters, Fishers and Farmers Party member who won the seat of Barwon during the March state election, said the existing plan may have a 40 billion litre a year hole in terms of over-allocated water.
What's needed now was a careful overhaul of the plan "based on the best scientific evidence we can find", not "populist slogans for more dams", Mr Butler said.
Comment has been sought from Energy and Environment Minister Matt Kean and from the NSW Irrigators Council.
'Appropriate' urgency
Rob Vertessy, a Melbourne University hydrologist who led a federal government inquiry into the Menindee fish kills last summer, said the report was "certainly timely and infused with the appropriate sense of urgency".
Among key recommendations that matched those of his report included modifying water access arrangements to protect low flows, maintaining connectivity of the rivers and protecting environmental flow, Professor Vertessy said.
The failures of the current plan include the lack of ecological targets and a failure to allocate water in line with Native Title for the river known as the Barka to the indigenous community.
For its part, the Murray-Darling Basin Authority said it did not have powers to assess the water-sharing plan because it was made before the wider basin plan came into force.
"The MDBA welcomes the findings and looks forward to seeing the new Water Resource Plan for the Barwon-Darling give effect to these important recommendations," a spokeswoman said.

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