What are the limitations?

Dr Perkins-Kirkpatrick said one of the limitations of climate change attribution studies is that they are heavily model-based.

"You have to be certain, or very confident at least, that that model is a good representation of the actual climate," she said.

"Unfortunately, however, no matter how good your model is, we simply can't really measure what the climate used to be like before climate change actually started."

There are some old observations, mainly in Europe, and paleo records, that are helping to improve knowledge in this area.

But our understanding of pre-industrial revolution conditions are not as good as our understanding of the current climate.

The type of event matters too.

Dr King said that hot or cold extremes are quite easy to attribute, especially on a big scale; other more variable events like rainfall, are more difficult.

"More complex events like fire weather, which has a combination of high temperatures, low humidity, strong winds — those are a lot harder."

Dr Perkins-Kirkpatrick also puts individual cyclones in the variable pile.

"It doesn't necessarily mean with those events that there is no anthropogenic signal," said Dr Perkins-Kirkpatrick.

"It just means that we can't yet detect it because there's a lot of variability overlying that particular signal."

And finally...

'Weather' vs. 'climate'

Communicating the difference between long term-climate trends and individual extreme weather events is where all of this gets messy.

The weather is what is going on day-to-day; the climate is what is happening over time.

Using the wardrobe analogy: climate is all of the clothes in your closet, while weather is what you wear each day.

Which raises the question: does every event need to prove or disprove climate change?

According to Dr Perkins-Kirkpatrick the answer is no.

"A lot of the events — I'm just saying a lot, I'm not saying all on purpose — would have probably occurred without climate change, but now they're occurring more frequently," she said.

"And that's exactly what attribution looks at: whether or not a particular event is occurring more frequently because of climate change,.

"We've always had tropical cyclones for example, they're always going to occur.

"It doesn't necessarily mean that every single tropical cyclone needs to be attributed to climate change."

"And we look at every event separately because they're all very different and very individual."

Likewise, not every cold snap means climate change is wrong.

"It's quite frustrating as a climate scientist to hear people saying that," Dr King said. "Especially if it's the president of the United States, it's not very helpful."

"We're always going to have that variable weather — even in a hundred years.

"It's just that the warm extremes are a bit warmer, the cool extremes are not quite as cold as they would've been in the past."

Both Drs King and Perkins-Kirkpatrick are trying to move away from publicly assigning a number or percentage to how much climate change has contributed to an individual event, despite media pressure.

Dr Perkins-Kirkpatrick said she understands the pressure from the media, "They want that analysis because it is interesting and it does show that climate change is actually happening now."

The researchers explain there is only so fast they can get such analysis done.

The problem keeps growing while we talk...

New findings show that the Great Pacific Garbage Patch, a rotating soup of plastic in the north Pacific Ocean, contains up to 16 times more waste than previous surveys were able to detect.

A team of scientists has conducted what they say is the most comprehensive study to date of the patch's size and the debris floating in it.

Using a combination of drag netting and visual surveys from boats and an aeroplane, they estimated the patch is 1.6 million square kilometres in area — almost the same size as Queensland.

Packed into this area is more than 78,000 tonnes of plastic, the researchers report in the journal Scientific Reports.

Most of the mass was made up of pieces larger than 5 centimetres. While microplastics, which account for about 8 per cent of the mass, made up a bulk of the estimated 1.8 trillion pieces of plastic floating in the patch.

Lead researcher Laurent Lebreton said the garbage patch was growing exponentially and was boosted by debris washed out to sea during the Japanese tsunami in 2011.

"We show that plastic concentration has been increasing exponentially since the 1970s for different reasons," said Dr Lebreton, an oceanographer at the Ocean Cleanup Foundation in the Netherlands.

"We correlated that with our model and we looked at estimates from the Japanese Government in terms of how much they think was washed to sea that day… and we predict that about 10-20 per cent of the materials post-2011 in the larger size class came from the tsunami."

Previous sampling, which estimated the patch contained around 4,800 tonnes of garbage, had primarily involved dragging funnel nets behind vessels to collect surface debris.

But Dr Lebreton said that this method excludes larger debris that cannot be collected by the nets, and that boat surveys can only cover a limited area.

"We saw that the surface area sampled by our trawls was not really large enough to be representative of the contribution of the bigger debris," he said.

"[So] we decided … to conduct an aerial expedition above the patch. We collected about 7,000 images [from the plane] and that helped us to calculate the contribution of larger debris such as ghost nets."

Continued

Clean-up operation needs to target source

By including the larger debris sizes in their study, the researchers knew they'd come up with a bigger figure than previous studies, but they were still surprised by just how much mass the larger debris contributed.

Almost half the larger debris they identified was commercial fishing gear including nets and fish aggregation devices — nets and other structure set adrift intentionally by fishers to attract fish.

Research scientist Dr Denise Hardesty from the CSIRO said it wasn't surprising the survey produced a much larger size estimate of the garbage patch, given the different research methods used.

"When you're comparing aerial surveys that are looking at ghost nets with estimates that are all focused on floating plastics we're not really making the exact same comparison," said Dr Hardesty, who was not involved in the study.

"Ghost nets will weigh so much more than all those little tiny bits and pieces and fragments."

But she says that the new research is still cause for concern.

"Whether you're focusing on count or mass, I think it is alarming and we all recognise that this is an increasing global project and it's going to take local solutions as well as hopefully global governance to help resolve the issues," she said.

Plastic circulating in the garbage patch does eventually get "kicked out" and washes up on coastline, Dr Hardesty said.

But right now we are feeding waste in at a much higher rate than it can be expelled.

"There's an increasing source that's coming from our coast. And yes shipping and fisheries waste is also contributing, but the lion's share of mismanaged waste is coming from land," she said.

The Ocean Cleanup Foundation said they would use the research to develop technologies that, they claim, would be able to "clean up 50 per cent of the Great Pacific Garbage Patch in five years".

http://www.abc.net.au/news/science/2018-03-23/great-pacific-garbage-patch-much-bigger-than-thought-study/9571234

An enormous amount of the plastic garbage in this patch that came from Japan was swept into the ocean as the Fukushima tsunami waters ran off the land they'd inundated.  No, that doesn't excuse Japan from any responsibility for helping to clean up this mess, but that was a significant contributor.

I still think it's necessary to construct a couple of ships specifically designed for this kind of clean-up operation. I very much doubt they will ever turn a profit, but the clean-up must be performed.

It's not about profit, it's about responsibility.

And given that a lot of the debris is fishing nets, then the fishing industry should at least make a start.

You get no opposition from me on this.  I just wish someone would take it on and manage to turn a profit, because then there'd be a commercial incentive, not merely a commonsense, practical, ethical, moral incentive.

Yes, I am very cynical where it comes to my fellow humans.

You might be able to get oil from the plastic, but I doubt it would be a very good grade.

The profit comes from not killing all the fish in the Pacific.

Then we can kill and eat them.

Most likely, the primary product we could make from recovered plastics would be more plastics.  Not all of them are bad for our world, but we have to start being careful what we do with the stuff.

So sad . . .

Game over