26/07/2017

Study: Our Paris Carbon Budget May Be 40% Smaller Than Thought

The Guardian - 

How we define “pre-industrial” is important
Participants looks at a screen projecting a world map with climate anomalies during the World Climate Change Conference 2015 (COP21). Photograph: Stephane Mahe/Reuters
In the Paris climate treaty, nearly every world country agreed to try and limit global warming to no more than 2°C above pre-industrial temperatures, and preferably closer to 1.5°C. But a new study published in Nature Climate Change notes that the agreement didn’t define when “pre-industrial” begins.
Our instrumental measurements of the Earth’s average surface temperature begin in the late-1800s, but the Industrial Revolution began in the mid-1700s. There’s also a theory that human agriculture has been influencing the global climate for thousands of years, but the mass burning of fossil fuels kicked the human influence into high gear.

We may be at 1°C or 1.2°C warming since “pre-industrial”
We know that since the late-1800s, humans have caused global surface temperatures to rise by about 1°C. But what about the human influence in the centuries before that, which are technically still “pre-industrial”? The new study used climate model simulations from 1401 to 1800, during which time we know the climate influences of natural effects like solar and volcanic activity fairly well. They found that depending on the starting point, global surface temperatures during that period were 0 to 0.2°C cooler than the late-1800s.
According to the last IPCC report, to have a 50% chance of staying below the 2°C target, when accounting for non-carbon greenhouse gases, we have a remaining budget of about 300bn tons of carbon dioxide. But that was for 2°C warming above late-1800 temperatures. If we add another 0.1°C of pre-industrial warming, the study authors estimated that the budget shrinks by 60bn tons (20%), and if there was an additional 0.2°C pre-industrial warming, the 2°C carbon budget shrinks by 40%. As one of the study authors Michael Mann put it:
Either the Paris targets have to be revised, or alternatively, we decide that the existing targets really were meant to describe only the warming since the late 19th century.
It’s an important point if we want to measure whether we’ve succeeded or failed in meeting the Paris climate targets. And it’s important to know if our budget should be set at no more than 300bn tons, or more like 200bn tons of carbon dioxide pollution.

We’re moving in the wrong direction
However, we’re not yet on track to meet the Paris climate target budget. Based on current national pledges, humans will cause around 3 to 3.5°C warming above late-1800 temperatures by 2100. However, the Paris treaty included a ratcheting mechanism through which countries can gradually make their carbon pollution targets more aggressive. If successful, that ratcheting could limit global warming to 1.8°C above late-1800 temperatures, which is likely less than 2°C above pre-industrial temperatures.
Global greenhouse gas emissions and 2100 temperatures under no action, current pledges (INDCs), and successful ratcheting scenarios. Illustration: Climate Interactive
To accomplish that goal, the US would have to ratchet its carbon pollution down to 45% below 2005 levels by 2030, for example. But at the moment, America is moving in the wrong direction, shamefully becoming the only nation announcing withdrawal from the Paris treaty, aiming to join Nicaragua (which declined to sign due to objections that the agreement was too weak) and Syria (which did not participate due to a civil war) as the only non-signatory countries. Fortunately, other countries like China and the EU are stepping up to fill the global leadership role vacated by America under the Trump administration.

Regardless, we need to cut carbon pollution ASAP
It’s also important to remember that 2°C isn’t a red line – that if we cause 2.1°C the world will end or that at 1.9°C everything will be fine and dandy. The 2°C target is a reasonable one for two reasons:
  1. Above about 2°C we start to get into the realm where there’s a significant risk of major climate impacts, like widespread coral bleaching, declining food production, significant sea level rise, and up to 30% of global species at risk of extinction.
  2. From a practical political standpoint, meeting the 2°C carbon budget is about the best we can do. Even that will require aggressive global action, with countries ratcheting down their carbon pollution targets.
But the key takeaway is that the more global warming we cause, the costlier and more damaging climate impacts will be. The faster we curb our climate pollution, the lower the risk of a climate catastrophe or especially damaging climate impacts.
We’re at the point where we need to cut carbon pollution as quickly as feasibly possible. That’s true whether Earth has warmed 1.0 or 1.1 or 1.2°C above “pre-industrial” temperatures. However, knowing which is the case is useful for setting concrete targets and evaluating whether we meet them. But if we’re going to meet them, we’ll have to quickly reverse the mistakes of the Trump administration.

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Extreme El Nino Events To Double In Number Even With 1.5-Degree Warming: Study

Fairfax - Peter Hannam

Extreme El Nino events will more than double in frequency, even with the most ambitious goals to curtail global warming, exposing large regions to severe droughts and placing coral reefs in peril, a team of scientists including Australians say.
In 2015, almost 200 nations signed the Paris Climate accord, agreeing to curb greenhouse gas emissions to prevent global temperatures warming more than 1.5-2 degrees compared with pre-industrial times. National pledges so far point to warming of closer to 3 degrees.
El Ninos are marked by abnormally warm temperatures in the tropical eastern Pacific that has global impacts. Photo: NASA
Even at the lower end of that range, which implies atmospheric levels of carbon dioxide peak by about 2040-2050 before starting to decline, big El Ninos will still become twice as common as their natural frequency to an average of about 10 per century and continue to rise further, according to research published in Nature Climate Change.
During El Ninos, the eastern equatorial Pacific is unusually warm, triggering a reversal of trade winds and a shift in rainfall patterns that often have consequences - such as droughts in Australia and the Horn of Africa, heavy rain in South America - well beyond the region. During extreme events, most recently in 2015-16, impacts can intensify.
"[During] big blockbuster El Ninos, if they happen more frequently, we can expect more damage and loss of life because of that," said Michael McPhadden, a senior scientist at the US National Oceanic and Atmospheric Administration and an author of the report that analysed 13 climate models.
"The number [of El Nino] might not necessarily increase but the stronger ones will get stronger," he said.
Cai Wenju, a principal research scientist at the CSIRO and one of the paper's lead authors, said the frequency of extreme El Ninos is beginning to emerge from the natural variability. There have been four such events since 1950 compared with one in the previous half century.
"To our surprise, if you stabilise GMT at 1.5 degrees, the extreme El Ninos continue to rise," Dr Cai said. "After that, the frequency of extremes rises another 40 per cent" to as often as one in every seven years before finally stabilising.
Aiming for that 1.5-degree warming cap is still worthwhile not least because the frequency of severe El Ninos will increase even faster if temperatures climb higher, Dr Cai said.
A young Somali girl displaced by drought wears mock spectacles cut from an antibiotics medicine box at a relief camp near the capital, Mogadishu, in March 2017. Photo: AP
Moreover, the flipside pattern, extreme La Ninas, do not increase in frequency at 1.5 degrees, the researchers found, but do so at higher warming levels. Complex circulation patterns mean the threshold for extreme El Nino events is more easily crossed with on-going warming than La Ninas.
"El Ninos are more sensitive to greenhouse forcing than La Nina but you'll reach a point where radiative forcing from excess greenhouse gas where both El Ninos and La Ninas will experience more extreme events," Dr McPhadden said.
Coral reefs, already struggling as water temperatures rise, will face severe threats during heat spikes, scientists say. Photo: WWF-Aus/BioPixel
Heat goes on
Apart from the regional impacts, El Ninos typically drive surface temperatures higher as the Pacific absorbs less of the excess heat being collected in the atmosphere from the additional greenhouse gases.
The past three years – 2014, 2015, and 2016, each broke annual records as the Pacific flirted and then fell into a full-blown El Nino. Even 2017 is likely to be among the hottest, with the first six months the second warmest on record, trailing only last year, NOAA said last week. (See NOAA chart below.)

Impacts
La Ninas have their own negative impacts, including above-average numbers of cyclones in northern Australia, but the global effects of El Ninos tend to be worse, Dr Cai said. That's even taking into account big floods in China in 1998 during a record strong La Nina.
"El Ninos tend to have huge areas of drought and the impacts may be more long-lasting than flood," Dr Cai said. With droughts, farmers may miss out on several planting seasons and natural eco-systems can take longer to recover compared with floods.
El Nino years have also seen severe coral bleaching and mortality as the corals respond to excess heat by expelling the algae that provide them with the bulk of their energy. As much as half of the Great Barrier Reef corals have died during the past two summers.
The rising background temperatures from climate change mean the heat spikes during El Ninos can be expected to make coral bleaching more common in the future.
"You  can envisage these kinds of impacts with the more frequent [extreme El Nino] events in the future," Dr McPhadden said.
The recent bleaching "was shocking how extensive it was, and how it affected so severely areas that had not been affected before", he said.
"Can they adapt? If not, there are some hard times ahead."

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Sea Level Warning As Greenland Darkens

BBC - David Shukman

The Greenland ice sheet covers an area about seven times the size of the UK. Kate Stephens
Scientists are "very worried" that the melting of the Greenland ice sheet could accelerate and raise sea levels more than expected.
They say warmer conditions are encouraging algae to grow and darken the surface.
Dark ice absorbs more solar radiation than clean white ice so warms up and melts more rapidly.
Currently the Greenland ice sheet is adding up to 1mm a year to the rise in the global average level of the oceans.
It is the largest mass of ice in the northern hemisphere covering an area about seven times the size of the United Kingdom and reaching up to 3km (2 miles) in thickness.
This means that the average sea level would rise around the world by about seven metres, more than 20ft, if it all melted.
That is why Greenland, though remote, is a focus of research which has direct relevance to major coastal cities as far apart as Miami, London and Shanghai and low-lying areas in Bangladesh and parts of Britain.
Algae were first observed on the Greenland ice sheet more than a century ago but until recently its potential impact was ignored. Only in the last few years have researchers have started to explore how the microscopically small plants could affect future melting.
A five-year UK research project known as Black and Bloom is under way to investigate the different species of algae and how they might spread, and then to use this knowledge to improve computer projections of future sea level rise.
The possibility of biologically inspired melting was not included in the estimates for sea level rise published by the UN's climate panel, the IPCC, in its latest report in 2013.
Scientists are investigating the different species of algae and how they might spread. Marian Yallop
That study said the worst-case scenario was a rise of 98cm by the end of the century.
One concern now is that rising temperatures will allow algae to flourish not only on the slopes of the narrow margins of the ice-sheet but also on the flat areas in the far larger interior where melting could happen on a much bigger scale.
We joined the latest phase of research in which scientists set up camp on the ice-sheet to gather accurate measurements of the "albedo" or the amount of solar radiation reflected by the surface.
White snow reflects up to 90% of solar radiation while dark patches of algae will only reflect about 35% or even as little as 1% in the blackest spots.
When we flew by helicopter onto the ice sheet, the rolling landscape seemed surprisingly grey - my first impression was that it looked dirty.
Much of the surface was covered with what looked like patches of soot and it was pockmarked with countless holes at the bottom of which were pitch-black layers of a mix of algae, bacteria and minerals known as cryoconite.
Prof Martyn Tranter of Bristol University, who is leading the project, told me:
"People are very worried about the possibility that the ice sheet might be melting faster and faster in the future.
"We suspect that in a warming climate these dark algae will grow over larger and larger parts of the Greenland ice sheet and it might well be that they will cause more melting and an acceleration of sea level rise.
"Our project is trying to understand just how much melting might occur."
Over the last 20 years, Greenland has been losing more ice than it gains through snowfall in winter - a change in a natural balance that normally keeps the ice-sheet stable.
Biological darkening has not been built into scientists' climate projections. Kate Stephens
 And one of the project scientists, Dr Andrew Tedstone, a glaciologist and also of Bristol University, said that over much of the same period, images from the MODIS satellite showed a darkening trend with the years of greatest dark producing most meltwater.
He said: "We still don't think we've reached a point where we've seen the maximum darkness that we're going to see in this area so the fieldwork we're doing is to try to find out in a warming climate 'do we think the area is going to get any darker than we've already seen in the last 15 years?'"
Earlier research had found that the ice sheet is covered with a range of contaminants carried on the winds including dust and soot from as far away as Canadian prairie fires and the industrial heartlands of China, America and Europe.
But studies over the past five years have shown that the majority of the dark material may be biological with different kinds of algae turning the ice black, brown, green and even mauve.
"This is a living landscape," according to Dr Joe Cook, a glacial microbiologist at Sheffield University.
"This is an extremely difficult place for anything to live but, as we look around us, all this darkness we can see on the ice surface is living - algae, microbes, living and reproducing in the ice sheet and changing its colour."
Ice retreat does not have to be total to have a damaging impact. Kate Stephens 
"We know they're very widespread and we know that they're very dark and we know that that's accelerating melt but that's not something that's built into any of our climate projections - and that's something that needs to change."
The final phase of the Black and Bloom project involves weaving the new factor of biological darkening into climate models to come up with revised estimates for future sea level rise.
And, as Dr Cook explained, the retreat of the Greenland ice sheet does not need to be total to have a widespread and damaging impact.
"When we say the ice sheet is melting faster, no one saying it's all going to melt in next decade or the next 100 years or even the next 1,000 years but it doesn't all have to melt for more people to be in danger - only a small amount has to melt to threaten millions in coastal communities around world."
Meanwhile, another factor that may be driving the melting has been identified by an Austrian member of the team, Stefan Hofer, a PhD student at Bristol.
In a paper recently published in Science Advances, he analysed satellite imagery and found that over the past 20 years there has been a 15% decrease in cloud cover over Greenland in the summer months.
"It was definitely a 'wow' moment," he told me.
Although temperature is an obvious driver of melting, the paper estimated that two-thirds of additional melting, above the long-term average, was attributable to clearer skies.
What is not known is how this might affect the algae. Their darker pigments are believed to be a protection from ultra violet light - so more sunshine might encourage that process of darkening or prove to be damaging to them.
The Black and Bloom project, funded by the Natural Environment Research Council (Nerc), aims to publish its new projections for sea level rise in two years' time.

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