There's another possibility of the event this author calls "river piracy." The Mississippi river is chronically at risk of being grabbed by the Atchafalaya River.
The Salton Sea is also an example. Its current incarnation was formed through accidental diversion of the Colorado River through an irrigation canal, and its continued existence is sustained through agricultural runoff from diverted Colorado River water. The Colorado River no longer reaches the Gulf of Baja in most years.
If you check out Google Maps, you'll see that the Colorado does in fact reach the Gulf of California. Not an impressive amount, but some. Enough that water clarity in the north part of the gulf is significantly worse than the south (a few feet versus tens of feet).
O/T: The Baja peninsula is great for camping except June-Aug, and I've spent ~15 weeks along [what we called] the Sea of Cortez. So, I went to wikipedia and apparently, it's gotten somewhat political. I can see both sides, but for other folks who like to lurk talk pages (the first thread is a discussion about what to call this body of water):
Loved that piece. It's part of a collection: The Control of Nature. Made me realize all the more that the life on planet earth isn't all about us and our little schemes.
"The calculations put chance of the piracy having occured due to natural variability at 0.5%. “So it’s 99.5% that it occurred due to warming over the industrial era,” said Best."
We need to train children in school to understand what statistical confidence means, so that we stop saying wrong things like this.
You can't say it's 99.5% due to global warming alone though. You can say 0.5% occurring by random chance but you can't just ascribe everything to one causal factor. Could be multi-factorial.
While the exact language in the quote is perhaps implying something, it only directly says the that the cause is warming during the industrial era. It doesn't provide any direct information about causal factors.
In the article: "So it’s 99.5% that it occurred due to warming over the industrial era," said Best.
I don't have a problem with them saying for example - "We believe that the river changed due to warming over the industrial era"
I don't really have a problem with anything they conclude to be honest, I was just answering another guy's question. Shitty of HN users to give me negative points over it. I feel like I'm on Reddit again.
That is possible. However in the abstract the author states
"Based on satellite image analysis and a signal-to-noise ratio as a metric of glacier retreat, we conclude
that this instance of river piracy was due to post-industrial climate change."
I played a game of Monopoly where I started with a roll of 12. There was a 97% chance I correctly rejected the hypothesis that the dice were fair. Maybe this is true in some sense? But it's still somewhere between misleading and nonsensical to say.
I think a better analogy is that it's like having many pairs of dice, and rolling each pair in turn until you get a roll of 12. Then concluding "this particular pair of dice must be loaded".
Presumably, the researchers did not select rivers at random to study, they selected this river in particular because of the changes it is undergoing.
Yes, I agree that p-value tests have flaws. If you look at the data to determine your hypothesis it's easy to overfit.
Bayes factor appear to solve this issue. I disagree that this is a basic education issue. It is a lack of agreement among scientists as to what statistical analysis is appropriate.
"So it’s 99.5% that it occurred due to warming over the industrial era"
There are at least a couple of statistical fallacies in this conclusion. And there isn't a lack of agreement about that.
One problem with p-value tests is precisely that people misunderstand what the p-value means, which is where basic education comes in. It could save people from believing a lot of things they shouldn't. (Like many health and fitness crazes over the last generation, for instance) Or at the very least, we could train science journalists.
I think you're mainly correct. The main issue is that there's an implied "given that the model from http://www.nature.com/ngeo/journal/v10/n2/full/ngeo2863.html is 'perfect' (at least for this case)". Since it seems unlikely that the model is perfect, the numbers they give are almost certainly inflated.
...as best I can tell, you have still swapped them? It sounds like you're still talking about P(null hypothesis|evidence), whereas p-values are about P(evidence|null hypothesis). (Well, not quite the latter but something like it.)
If you look at 200 rivers, it would not be surprising to find something that naturally occurs 0.5% of the time. It is not correct to say that there is a 99.5% chance that this is due to non-natural causes.
The wording is ambiguous. In general, trying to determine whether a statement about probability is correct or not requires more information than can be encapsulated in a single sentence. The English language does not help in this.
We're not going to get more information here without someone looking into where the .5% number comes from.
The method of Roe et al. is summarized as follows. Let 1L be the change in
glacier length over the past 130 years (∼1.9 km), and let σL be the standard
deviation of glacier length due to stochastic fluctuations in mass balance, b, from
natural, interannual climate variability. The signal-to-noise ratio is defined by
sL =1L/σL
. Likewise, sb =1b/σb
. Ref. 12 demonstrates that the two are related via
sL =γ sb
, where γ is an amplification factor that depends only on the duration of
the trend and the glacier response time, τ . The probability density function (PDF)
for sb
is generated by combining the signal-to-noise ratios of the observed
melt-season temperature and annual-mean precipitation trends, normalized by the
summer (bs) and winter (bw ) mass-balance variability (Supplementary Fig. 1a,b,c),
respectively. We take σbw = 0.3 myr−1
and σbs =0.5 myr−1
, based on the observed
mass-balance variability at Gulkana Glacier and the analysis of the global datasets
of glacier mass balance33. The glacier response time is given by τ =−H/bt
, where
H is a characteristic glacier thickness, and bt
is the (negative) net mass balance at
the terminus. We set H=590 m, based on the scaling relationship for glacier
geometry suggested by Haeberli and Hoelzle34 and measured cross-sections35; and
we set bt =−7 myr−1
, estimated by extrapolating the vertical mass-balance profiles
calculated by Flowers et al.8
, thus giving a central estimate for τ of ∼80 years. A
PDF is estimated assuming τ follows a gamma distribution incorporating a broad
uncertainty of στ =τ /4 (Supplementary Fig. 1d). The PDFs for γ and sb are
combined to give a PDF for σL
from the relation σL =γ 1L|
obssb
. This, in turn, is
used to evaluate the null hypothesis that 1L|
obs occurred due to natural variability.
Supplementary Fig. 1e shows our estimate that there is only a 0.5% chance
that the observed retreat of Kaskawulsh Glacier happened in the absence of a
climate trend.
The 0.5% quote is fine. It's turning it into a 99.5% that is not fine.
It's essentially like saying that a pair of dice that rolled a 12 has a 97% chance of being loaded, because there's only a 1 in 36 chance of rolling that high.
Let's assume that when a river gets redirected, a scientist goes and investigates it (which seems reasonable), and is asked what is the chance that it happened by natural causes, or is due to global warming. Based on the analysis that @acover shared with us, we can see that out of a thousand such dispatches, 995 will be due to global warming and 5 will be due to natural variability. So it seems correct for that scientist to conclude "It's 99.5% due to global warming.". In fact, saying that it's .5% due to natural variability is equivalent.
You are probably thinking of the jelly bean situation, where a test is performed to detect something within a sample population. The test has a failure rate, and the population has a base rate of occurrence.
In this case (thanks @acover), they are directly calculating the base rate.
Now, you could also ask "How many times in a year will a scientist be dispatched and be wrong", which is a again a different question (and is closer to the scenario you described).
I am out of my depths but I do not think you are correct.
The paper appears to create a model for a single glacier's retreat. Selects the parameters of this model by analyzing all glaciers. Then determines the retreat of this glacier is unlikely under this model.
The issue is that there is a sampling bias. This glacier is not like most glaciers [I assume]. It was not randomly sampled from all glaciers. It was selected because of a river diversion due to glacial retreat.
What did they do to compensate for this sampling bias? I don't see it.
>Let's assume that when a river gets redirected, a scientist goes and investigates it
This is a faulty assumption and is what leads to the wrong conclusion. The probability of 0.5% is for a randomly selected river. That is, if you went and examined 200 randomly selected rivers, 1 of them (on average) would be redirected due to natural variability.
That does not imply that the remaining 199 were redirected due to global warming. It does not even imply that the remaining 199 were redirected at all!
What is needed is the percentage of rivers that have undergone this redirection. Here's a simplified example: If it's ~0.5%, you conclude it's just natural variation. If it's >0.5%, you conclude that something (possibly global warming) is increasing the number of rivers that are being redirected. If it's <0.5%, you conclude that something is decreasing the number of rivers that are being redirected.
"shows our estimate that there is only a 0.5% chance that the observed retreat of Kaskawulsh Glacier happened in the absence of a climate trend"
The 0.5% has nothing to do with the river. It is their confidence that the retreat of the glacier could occur in the absence of a climate trend based on their model.
Can you clarify why it is incorrect to reverse that into the statement "We estimate that there is a 99.5 percent chance that the observed retreat did not happen in the absence of a climate trend."? I confess to a fair amount of confusion at this point :) I'm sure there is something subtle (or perhaps obvious, and my brain is failing) that I'm missing.
Oh I thought we were having an interesting discussion about the linguistic mapping between probability and regular English. Sorry for wasting your time. :(
> The probability of 0.5% is for a randomly selected river
Sorry, what is the probability .5% for exactly? The probability a river is redirected under global warming conditions? I didn't think that's what they computed. If it is, then my bad. :) I thought they had computed given that the river was redirected, what is the likelihood it happened due to global warming. Ah well, like I said, the details are the hard part. :)
This kind of thing has happened several times in China in recorded history with the Yellow River, to the point where sometimes the river has flowed into the ocean north of the Shandong peninsula and sometimes south of it.
The re-routing of rivers within their deltas, due to sediment deposition, is how deltas get to be delta-shaped. The thwarted (at least for now) capture of the Mississippi by the Atchafalaya, mentioned on another comment, would have been another example of this.
I was just looking at the Alsek valley on Google Earth the other day. It's (obviously) a water-level route from behind the mountains to the coast, and abuts the drainage divide with the Yukon.
The entire Alsek-Tatshenshini-Kaskawulsh-Dezadeash system's upper reaches occur in glacier-scoured valleys so ice damming or stream undercutting could greatly change the direction rivers flow. The northwest-southeast trench that includes Kluane Lake and continues beyond Haines Junction is the Shakwak Trench [4], created by the Denali fault.
Here's a map of the article's glacier and the surrounding area: http://i.imgur.com/tL84Bd0.jpg (edited from the park map [1])
Meanwhile, 90 kilometers downriver (south) along the Kaskawulsh->Alsek, the west-to-east Lowell Glacier used to squish the north-to-south Alsek River against the far valley wall, damming it and causing a lake to extend upstream [3]-- the last time this happened was around 1850; the source estimates it'd take a year of being dammed for lake to extend up the Dezadeash to Haines Junction.
Rivers have historically meandered. They didn't have a set path. The modern expectation that rivers have a set path is one we tend to try to actively enforce.
Elsewhere in comments here, someone noted that the Salton Sea is similar. But if you read Salt Dreams, Native Americans had oral history suggesting that there had been a lake there previously. Geological records agree with the oral history.
Sweet, so what should we build to change this? Giant carbon-sucking machines, cube-sats pointed at glaciers? (planet labs is doing cool stuff in this space, including a project to count every tree on Earth every day).
Solutions welcome!
- Burn fewer fossil fuels (less driving, flying, heating, cooling, more wearing sweaters at home in winter, etc)
- Eat less meat
- Develop technologies to create energy without fossil fuels
At a higher level
- Stop associating consumption and material accumulation with happiness
- Stop targeting growth (population, GDP, etc) as solution to so many problems
- Take personal responsibility for what you do. Stop saying if others don't change my change won't make a difference. You are responsible for what you do even if others don't change.
At the top level:
- Change you beliefs and goals so that instead of asking others, you find what you can do and do it. There is overwhelming amounts of information for what you can do already on the web. If you want to act, act.
I'm not convinced having fewer children will help anything and I wish people would stop repeating this. People emit very few greenhouse gasses as a virtue of their existence, the extreme majority of them are emitted by lifestyle choices.
Even in developed countries the differences are stark. Qatar emits 54.7 tons of CO2 equivalent per capita, the United States 24.3 tons, Germany 12.3 tons, Switzerland 7.2 tons. A difference of almost 10x, with countries that all have similar standards of living! In a relatively undeveloped country like Burundi, the emissions are a mere 0.4 tons per capita[0]. A difference of literally 100x!
The best fix is a revenue-neutral carbon tax, with import tariffs on goods from countries that do not have such taxes (i.e. China). This internalizes the externalized costs of CO2 emissions, automatically encouraging development of more energy-efficient everything.
Having fewer children is throwing the baby out with the bathwater. The only reason we care about the environment is because it serves people. It's like trying to prevent cancer by having fewer children - fewer people will suffer from it!
Children are also important to us adults. We need them to indirectly take care of us when we're old by keeping the economy around us functioning and providing services and for us. Some western countries are facing potential problems with aging populations and not enough young people to support them. That's big and important. Possibly more important than global warming. There's no point having a stable environment if you die from a treatable disease because there are no doctors available.
Whenever there's a problem or a risk, and you're deciding what to do about it, one option is always "do nothing". We don't _have_ to stop climate change. If stopping it causes more harm that letting it continue, then we would be wrong to stop it.
Perhaps what we really need is political will. It has been much said in the UK that wind power has made various great strides forward, in terms of being able to operate in a greater range of wind speeds for example. This is in pursuit of EU green energy targets. With Brexit it sounds like the government are keen to resort to fossil fuels. Luddites
Technology is not the biggest challenge to reforesting, people are. What good is planting millions of trees with robots if poor peasants graze their goats in the area that kill them all? To succeed you need to get them to buy into the outcome.
China's efforts on the Loess Plateau has been held up as a success in reforestation which has also benefited the local agricultural economy.
"The area of restoration on the Loess Plateau in China is the size of Belgium and thousands of years of subsistence farming had made it barren and infertile. In 1995 the Chinese Government, with support from The World Bank, took drastic action to rehabilitate the plateau, and local people -- seen as both perpetuators and victims of the devastation -- became part of the solution. They completely transformed 8.6 million acres of wasteland into hyper-productive land. This caused a 300% increase in agricultural income and enabled millions of local family farmers to break free from entrenched poverty."
Thanks, I watched the whole video. A great success of natural capitalism. I wonder how drone surveys, satellite mapping, and synthetic biology could extend this 35 sq-km success to 3,500 sq-km and beyond, augmenting people's needs and efforts. As said in the video, let's "properly understand the miracles performed by trees" to make this more
profitable and spread everywhere.
I also agree with the farmer who said "what about our children, they can't eat trees!!". There's an opportunity for climate change solutions need to be communicated at human timescales (days, months, years). Decades are too hard to imagine.
Perhaps its not exactly the best example of capitalism given that it was centrally planned.
Glad you found it interesting. In the text accompanying the video they link to more videos in the series from Ethiopia and Rwanda, with similar projects to rehabilitate the land.
For the latter, I think the research and other work for using Paulownia trees for carbon sequestration qualifies. I do seem to recall that there was some attempt to further cultivate it to be more suitable for that purpose.
One challenge with plant-based sequestration is that the carbon is released when the tree dies/decomposes. I wonder how planting more trees will balance out at the decade-century scale.
Wow cool, at first I said "but the CO2 gets released when the building burns down", so I looked into it.
Apparently wood has a ton of benefits, basically it doesn't release much of the CO2 if it just sits there (http://www.awc.org/pdf/education/gb/ReThinkMag-GB500A-Evalua...).
And it takes far
less energy to grow a tree than the respective amount of concrete/other building materials (http://www.treehugger.com/green-architecture/new-study-confi...).
So wood->building materials is a great option. Right on!
"Since it is generally advantageous to have a heterogeneous mix of tree species planted in the same area, the planting UAV is capable of carrying a mix of seeds and control their planting pattern."
We should do nothing, because while interesting, this is a nonevent. Parts of that article are wildly exaggerated or outright incorrect, trying to make this sound like some big deal. It's really not.
Sometimes in nature, things happen quickly. Look up glacial surge, for example. Just because a river dried up basically overnight because it got beheaded, it doesn't mean there's some global catastrophe playing out. It just means the glacier receded to a point where the terrain favored the other branch.
Guys, I seriously do not know wtf happened. I never opened this "Receding glacier" thread. I was commenting on the Intel thread and my comment somehow ended up here. I got aware of it because of all these negative points which came quite unexpected.
I'm not sure what might've happened, but the web request logs show that comment being submitted to this thread. We've restored your karma and moved your comment to the right thread.
Are you serious right now? Global warming isn't just a moment in history, it's a process that has been happening over the years, with rising sea levels and land sinking in a lot of countries.
I guess you are just one of those people who fail to acknowledge it unless it's your own home slowly getting submerged under water.
Shame, it was flagged and removed. It was a comment that was highly sarcastic and critical of climate change, but I'd say no more sarcastic than any other comment we might find on here. Perhaps we could have benefited from learning why people continue to falsely believe climate change isn't real.
"Booo it's the ghost of global warming! Always threatening, never happening." is a worthless pointless comment and there's not going to be any useful discussion coming from it.
It's exactly the kind of comment that needs to be downvoted and flagged.
Also, flagging doesn't really remove anything. You can change the "showdead" setting in your options to see all flagged comments.
Lol "immense" river 150m wide. Ok guardian readers, that may be an immense and scary river in the UK but canadians reserve words like immense for far larger things. At 15km this river may well be the largest thing ever seen by a brit, but canada has something like 50 rivers over 350 miles long. This is a glacial stream by the standards of The North, a part of canada bigger than all western europe. My local dog beach has a river 150m wide.
The River Thames is wider than 150m inside of London. The London Bridge is over 250m long[1]. It is rather wide given its proximity to its headwaters but not on an absolute scale, even by British standards.
Idiots no, but given how UK publications so often describe geographical features one is left with the impression that the UK is sized like legoland. This is not a large river and, given the climate change aspect to the story, to desribe it as such is dishonest.
Hrm, I'd hate to say it like this but it's not always the length that matters. Did you read the bit about the volume of water that the pirating river increased by?
John McPhee wrote about this in 1987. http://www.newyorker.com/magazine/1987/02/23/atchafalaya