10/04/2017

New Study Links Carbon Pollution To Extreme Weather

The Guardian - 

Human activities are altering the jet stream, which leads to extreme weather patterns getting stuck in place
Parts of Lismore, Australia affected by floodwaters on April 2, 2017. Photograph: Jason O'Brien/Getty Images
It was only a few weeks ago that I wrote about changes to extreme weather in a warming world. That prior article dealt with the increase of extreme precipitation events as the Earth warms. I termed the relationship a thermodynamic one; it was driven by local thermodynamic processes. But extreme weather can also occur because of large-scale changes to the atmosphere and oceans. This issue is the topic of another just-published paper that makes a convincing case for a whole new type of influence of humans on extreme weather. In a certain sense, this study confirms what was previously reported here and here. With the march of science, the tools, methods, and evidence get better each year.
Before getting into the study, a little background. The jet stream(s) are high-speed rivers of air that flow in the upper atmosphere. There’s more than one jet stream; they blow west to east and they mark the separation of zones of different temperatures. A good primer on jet streams is available here.
If you were to stand at the northern pole and travel southwards, you would experience a gradual increase in temperature. However, when you reached the first jet stream (the Polar Jet), temperatures would rapidly become warmer. That is, the Polar Jet separates two different temperature air regions. Typically, if you are north of the jet stream, you are in a colder zone whereas if you are south of the stream, it is warmer. Sometimes, the jet streams undulate as they encircle the planet and these undulations move. So, sometimes you happen to be in a position north and sometimes south of the stream, even though your location is fixed.
Diagram of undulating jet streams. Illustration: National Oceanic and Atmospheric Administration
The interface between warm and cold temperatures creates a lot of weather-pattern changes. In addition, if the undulations of the streams become fixed, it means your weather patterns will get stuck. For instance, you could find yourself in an upward undulation for weeks or longer and experience warm and potentially dry weather. Alternatively, if your location is north of a stuck jet undulation, you may experience persistent cold weather. Perhaps even more importantly, these stuck waves can become larger in their magnitude.
So, scientists really want to know what affects these undulations – both their magnitudes and their persistence. We also want to know whether these undulations will change in a warming planet. This is precisely where the new study comes in. The researchers used both weather observations and climate models to answer these questions. What they found was very interesting.
Using measurements, the authors documented what conditions led to extreme weather patterns that persisted for extended durations. They found that many occur when the jet stream becomes stationary with the undulations stuck in place. They also saw that under certain situations, the jet stream undulations do not dissipate in time; they become trapped in a wave guide.
Interestingly, this pattern of a stuck jet stream would occur when the number of undulations was between six and eight. When these circumstances all lined up, according to study co-author Stefan Rahmstorf:

the same weather persists for weeks on end in one region, then sunny days can turn into a serious heat wave and drought, and lasting rains can lead to flooding
And this is also how humans come into the story. As humans emit greenhouse gases, the planet warms. We know that, we predicted it, and it is occurring. However, the warming is not uniform. The Arctic, for instance, is warming more rapidly than the rest of the planet. As a result, the temperature difference between the Arctic and the rest of the world is reducing. It is this temperature difference that maintains the jet stream patterns. As stated by lead author, Michael Mann:

The warming of the Arctic, the polar amplification of warming, plays a key role here. The surface and lower atmosphere are warming more in the arctic than anywhere else on the globe. That pattern projects onto the very temperature gradient profile that we identify as supporting atmospheric waveguide conditions.
The authors compared the observations to computer models and they found similar patterns. The authors went on to say in a press release:

Using the simulations, we demonstrate that rising greenhouse gases are responsible for the increase ... We are now able to connect the dots when it comes to human-caused global warming and an array of extreme recent weather events.
This is really where the science is. We know humans are causing climate change and we know that weather will change as this process evolves. What we really want to know is how human-caused climate change will influence extreme weather. It’s extreme weather like droughts, floods, heat waves, etc. that cause high social and economic costs. These authors have concluded a convincing study that connects the dots. Perhaps the study is best summarized by Michael Mann, who said:
We came as close as one can to demonstrating a direct link between climate change and a large family of extreme recent weather events.
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'Disaster Alley': Cyclone Debbie Shows How Climate Change Will Test Australia's Military

Fairfax - Peter Hannam

As Rockhampton residents braced for a nine-metre-high major flood this week, efforts were bolstered by some of the 1600 Australian Defence Force troops deployed to help cope with Cyclone Debbie and its aftermath.
In the past fortnight, the military dispatched helicopters, four landing craft, two larger naval ships and conveys of heavy vehicles to deliver water, medicine and other emergency supplies after the category four storm hit.

Cyclone Debbie by the numbers
Since Cyclone Debbie struck in late March, extreme weather has wreaked a path of destruction across Queensland and New South Wales.

"Only the military has the large-scale capability of relief response," Michael Thomas, a retired army major, said.
It's a capability that has been tested in recent years, whether from category five Cyclone Winston that smashed Fiji last year or the huge El Nino which brought severe drought to Papua New Guinea.
And the challenge might have been made even tougher had Cyclone Ernie – which rapidly intensified this week into a category five tempest – not turned away from the Australian continent when it formed off the WA coast this week. A weaker but still dangerous cyclone is heading towards Vanuatu this weekend.
"Disaster relief is increasing in frequency and scope and scale," said Mr Thomas, who will publish a book on the US and Australian readiness for climate change in June.

'Disaster alley'
Australia lies in the midst of what Sherri Goodman, a former Deputy Under Secretary of Defence for environmental security in the US, dubs "disaster alley".
The region is home to large and swelling populations in coastal and delta regions exposed to cyclones and other extreme weather. These events are predicted by scientists to worsen with global warming.
An Australian Army Mercedes Benz G-Wagon disembarks landing craft at the Keppel Bay Marina, Yeppoon, Central Queensland, bound for Rockhampton. Photo: Abis Bonny Gassner
Ms Goodman, who met senior Australian military members during a visit this week to Canberra, noted admiral Samuel Lockler III, the former head of the US Pacific Command, had described climate change as the biggest long-term security threat in the region.
"The Australian military and the Department of Defence are very interested to be leaders" on this issue, she said. "They know it's the right thing to do."
Taking direction: The Australian Defence Force deployed about 1600 troops to help communities with Cyclone Debbie's aftermath. Photo: Australian Defence Force
Fairfax Media sought comment from the ADF.
Ms Goodman coined the phrase "threat multiplier" a decade ago as the Pentagon stepped up efforts to focus on planning for the consequences of a warming world.
The Australian Defence Force aircraft on hand to assist with the ex-tropical Cyclone Debbie's clean-up. Photo: Australian Defence Force
Among the challenges is the vulnerability of military assets themselves, such as naval bases that are at risk from rising sea levels and storm surges, she said.
Armed forces must also prepare for greater instability as fragile nations become more unstable through crop failure or forced migration within and across borders.
Sherri Goodman, a former Deputy Under Secretary of Defence for environmental security in the US, says Australia lies in "disaster alley". Photo: Wilson Centre
And militaries such as Australia's will need to be ready to divert more personnel and equipment to meet disaster relief needs both at home and abroad, Ms Goodman said.

'Significant impacts'
David Titley, a retired US admiral, said regions between 30 degrees north and south of the Equator are among the most vulnerable on earth to climate change.
"[It's] where precipitation is likely to decrease, temperatures will increase in some places to near lethal levels, and potentially stronger tropical cyclones will come ashore on an ever-higher sea level," Admiral Titley said.
"Much of Australia is poleward of 30 degrees South, so there will likely be significant impacts to your country - but there will be large impact throughout South and Southeast Asia," he said.
Mr Thomas, who last year inaugurated a week-long climate change and security course at the Australian Defence College, said Cyclone Debbie also served as a reminder that military bases "are not islands".
They remain reliant to varying degrees on civilian infrastructure such as electricity, water and sewerage systems that could be disrupted by big storms.
Similarly, their staff, whether civilian or military, "have to be able to get to the bases" – something that's not always possible when bridges or roads are damaged or destroyed by extreme weather, he said.

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