What methods are used to determine how much of climate change is man-made?

[hololeap]

I will admit that I am skeptical about man-made global warming, but not because I am in denial, nor because I am an idiot, nor because I am in bed with the oil industry. I simply haven't been given a satisfying explanation of why scientists believe that man is the biggest contributor to present global warming. Most of the websites and videos on the subject are full of reference to the scientific consensus, emotional pictures (think: polar bears swimming and cooling towers), and maybe a simple explanation of how the greenhouse effect works or a graph showing CO₂ going up along with temperature towards the end of the last century.

 

None of this proves that man is the biggest contributer to global warming, and I find it insulting that so many major websites avoid educating the public, especially when there is such a political push to "stop climate change". So, what leads the 97% of scientists to believe that man is the biggest contributor? How is it determined how much of the present greenhouse gasses are from humans and how much are from, say, volcanic activity? Is it hypothesized that man-made global warming would have specific effects on the atmosphere that differ from natural warming cycles? If so, have these been observed?

 

I admit that I have not been able to get through any white papers on the subject because I am not familiar with the technical terminology, so I am hoping to get a complete explanation, but using terms that a college freshman could understand. Thanks!

[Essay]

I will admit that I am skeptical about man-made global warming, but not because I am in denial, nor because I am an idiot, nor because I am in bed with the oil industry. I simply haven't been given a satisfying explanation of why scientists believe that man is the biggest contributor to present global warming. Most of the websites and videos on the subject are full of reference to the scientific consensus, emotional pictures (think: polar bears swimming and cooling towers), and maybe a simple explanation of how the greenhouse effect works or a graph showing CO₂ going up along with temperature towards the end of the last century.

 

None of this proves that man is the biggest contributer to global warming, and I find it insulting that so many major websites avoid educating the public, especially when there is such a political push to "stop climate change". So, what leads the 97% of scientists to believe that man is the biggest contributor? How is it determined how much of the present greenhouse gasses are from humans and how much are from, say, volcanic activity? Is it hypothesized that man-made global warming would have specific effects on the atmosphere that differ from natural warming cycles? If so, have these been observed?

 

I admit that I have not been able to get through any white papers on the subject because I am not familiar with the technical terminology, so I am hoping to get a complete explanation, but using terms that a college freshman could understand. Thanks!

 

If you have some particular curiosity about the details, ask away; but in general:

They can tell how much CO2 comes from burning fossil fuels, because that carbon has a different “isotopic signature” than volcanic (or other) sources of CO2. So when they say we are adding ‘over 30 billion tons’ of CO2 each year, to the atmosphere, they can fairly well account for it all on the balance sheets of giant corporations who pay to dig it out of the ground.

 

As to the effect it is expected to have on the climate, there are theoretical predictions (based on the spectroscopic properties of “greenhouse” gases) that also agree fairly well with the geological record, which show how CO2 keeps the planet about 10 – 15 degrees warmer than it would be without CO2. There is lots of evidence, from many different sources, across many disciplines, and over a century, which all lead fairly narrowly to the same conclusion …that “consensus” view.

 

Probably, when you hear about 'man-made' global warming being different (from "natural warming cycles"), it is referring to the extreme rapidity (relatively, on a geological scale) that our contribution to the planetary cycles is occurring.

 

 

http://www.nature.com/scientificamerican/journal/v305/n1/box/scientificamerican0711-56_BX1.html

 

...not counting the meteor that wiped out the dinosaurs....

The "PETM" (in blue) is the most comparably drastic geologic analogy, which exists for us to compare and judge "rapid change" by.

 

~

[hololeap]

They can tell how much CO2 comes from burning fossil fuels, because that carbon has a different “isotopic signature” than volcanic (or other) sources of CO2. So when they say we are adding ‘over 30 billion tons’ of CO2 each year, to the atmosphere, they can fairly well account for it all on the balance sheets of giant corporations who pay to dig it out of the ground.

 

That makes perfect sense. Thanks for the info.

 

My next question is:

How can scientists determine how much humans have impacted the temperature of the planet? Putting all the speculation of the future aside, I would think that in order for the AGW conclusion to hold any weight, there must be some value or range of values calculated for the amount human activity has brought our current temperature above where it "should be". Given all the driving factors for global warming, how can they do this?

 

I can understand that greenhouse gasses are a significant driver of global warming and that humans are a significant creator of greenhouse gasses. But, to conclude that human activity is significantly driving climate change seems, at best, an educated guess. Are there other ways of testing this hypothesis besides measuring the amount of greenhouse gasses we have released into the atmosphere?

Edited August 12, 2014 by hololeap

[swansont]

 

I can understand that greenhouse gasses are a significant driver of global warming and that humans are a significant creator of greenhouse gasses. But, to conclude that human activity is significantly driving climate change seems, at best, an educated guess. Are there other ways of testing this hypothesis besides measuring the amount of greenhouse gasses we have released into the atmosphere?

 

It's not an educated guess, though, it's science, and it's far more involved than you're realizing. Scientists are not only measuring the greenhouse gases, they're measuring the other effects, too. The planet is heating up, which we can measure. We can measure the incoming solar radiation and measure what's leaving, which tells us how much of an energy imbalance there is, and how much the planet should warm up. You can test the various contributions from other effects that would change the temperature. What they've found is that it's not only that the anthropogenic greenhouse gases cover the increase, it's also that no other effects can explain it. Solar radiation has not increased, for example, so it can't be that.

 

Another common objection is that it's just a few parts per million of CO₂, so what's the big deal? The amount of sunlight reaching the top of the atmosphere is around 1.35 kW/m². Some is reflected and some absorbed, and about a 1 kW gets through. It only requires an increase of about a Watt to increase the temperature by 1 ºC. A tenth of a percent. So small changes are crucial.

[hololeap]

Another common objection is that it's just a few parts per million of CO₂, so what's the big deal? The amount of sunlight reaching the top of the atmosphere is around 1.35 kW/m². Some is reflected and some absorbed, and about a 1 kW gets through. It only requires an increase of about a Watt to increase the temperature by 1 ºC. A tenth of a percent. So small changes are crucial.

 

No, I understand that a small change can create a big effect. The whole reason I have been skeptical is because of the sheer level of emotional propaganda around global warming and little information about the science behind it. I remember seeing Al Gore having to use a cherry picker because his graph was too damn big, and thinking, "is this trying to scare me?" Then, I went to the various major websites to learn more, and all I got was information about the scientific consensus, but nothing to tell me why I should reach the same conclusion. Then, I see the pictures of the smokestacks and polar bears, the videos with ominous music and cars on the freeway zoomed too far in so you can see the heat distortion, the pictures of ostriches with their head in the sand implying that anyone who doesn't immediately believe the hype is an idiot, and still no real information about what evidence is leading the 97% of climate scientists to agree that AGW is a real phenomenon... it led me to be very suspicious and think that there was very little science behind the hype. I guess I was just looking in the wrong places for information.

 

I still have some more questions about AGW, but I am going to continue to research this on my own and see what I can find for myself and then come back to this thread if I have any unanswered questions. There does seem to be more relevant, easy to understand information online than there used to be. But, I think that anyone who is a climate scientist or has any power within the scientific community should heavily discourage the kind of hype that is going on around AGW. It dilutes the facts and makes logical, intelligent folks highly skeptical since there is more out there trying to scare the public rather than educate them.

Edited August 12, 2014 by hololeap

[timo]

You could try this little tousand-page handbook: http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm . It's a report of many of those 97% of scientists in which I believe they try to explain what leads them to their concensus. Should lie somewhere between the white papers and the polar bears that impressed you so much. But I must admit I did not completely read it before proposing the link

[Johnny Electriglide]

This place has many answers if you scroll around

https://www.skepticalscience.com/

It does not have everything, like the Arctic Methane Emergency.

The IPCC is politically motivated to be overly conservative with their projections,

and they do not figure in geometric methane release, or over-population's realities.

Edited August 12, 2014 by Johnny Electriglide

[swansont]

 

No, I understand that a small change can create a big effect. The whole reason I have been skeptical is because of the sheer level of emotional propaganda around global warming and little information about the science behind it. I remember seeing Al Gore having to use a cherry picker because his graph was too damn big, and thinking, "is this trying to scare me?" Then, I went to the various major websites to learn more, and all I got was information about the scientific consensus, but nothing to tell me why I should reach the same conclusion. Then, I see the pictures of the smokestacks and polar bears, the videos with ominous music and cars on the freeway zoomed too far in so you can see the heat distortion, the pictures of ostriches with their head in the sand implying that anyone who doesn't immediately believe the hype is an idiot, and still no real information about what evidence is leading the 97% of climate scientists to agree that AGW is a real phenomenon... it led me to be very suspicious and think that there was very little science behind the hype. I guess I was just looking in the wrong places for information.

 

I still have some more questions about AGW, but I am going to continue to research this on my own and see what I can find for myself and then come back to this thread if I have any unanswered questions. There does seem to be more relevant, easy to understand information online than there used to be. But, I think that anyone who is a climate scientist or has any power within the scientific community should heavily discourage the kind of hype that is going on around AGW. It dilutes the facts and makes logical, intelligent folks highly skeptical since there is more out there trying to scare the public rather than educate them.

 

The flip side of this is that a large swath of the deniers are not convinced by fact; to them this is an emotional issue, not a rational one. The ones convinced by facts aren't necessarily the target of the hype. And then there is the campaign of the deniers, which is very heavy on hype and almost entirely devoid of fact.

[timo]

The IPCC is politically motivated to be overly conservative with their projections,

and they do not figure in geometric methane release, or over-population's realities.

I am not sure what your objection is, or even if this actually is supposed to be an objection to the link. Do you believe the IPCC report fails to explain "what leads the 97% of scientists to believe that man is the biggest contributor"? I cannot tell, but I expected the report to be a good, rough, 1000-page long overview, assuming hololeap does not want to go into all details. Or are there not enough pictures of polar bears? [*] I do not know exactly what hololeap is looking for - and the thought occurred that hololeap is not actually looking for information at all but rather trying to make a point. But I think a webpage complaining about global warming sceptics getting an over-proportionate amount of media coverage or covering studies indicating that republicans might be convinced of global warming with proper education may be a bit too meta.

 

[*] Yes, I will mention the term "polar bear" in every post in this thread. I'll even post a picture as a measure of last resort

[factseeker88]

I will admit that I am skeptical about man-made global warming, but not because I am in denial, nor because I am an idiot, nor because I am in bed with the oil industry. I simply haven't been given a satisfying explanation of why scientists believe that man is the biggest contributor to present global warming. Most of the websites and videos on the subject are full of reference to the scientific consensus, emotional pictures (think: polar bears swimming and cooling towers), and maybe a simple explanation of how the greenhouse effect works or a graph showing CO₂ going up along with temperature towards the end of the last century.

 

None of this proves that man is the biggest contributer to global warming, and I find it insulting that so many major websites avoid educating the public, especially when there is such a political push to "stop climate change". So, what leads the 97% of scientists to believe that man is the biggest contributor? How is it determined how much of the present greenhouse gasses are from humans and how much are from, say, volcanic activity? Is it hypothesized that man-made global warming would have specific effects on the atmosphere that differ from natural warming cycles? If so, have these been observed?

 

I admit that I have not been able to get through any white papers on the subject because I am not familiar with the technical terminology, so I am hoping to get a complete explanation, but using terms that a college freshman could understand. Thanks!

The only proof that global warming scientists have is what they learn in their labs. Outside their labs in the world wide environment, their lab tests are worthless.

 

“No lesson is so deeply inculcated by the experience of life as that you should never trust experts.” Lord Salisbury.

 

"Question everything." TV Science channel

[swansont]

Thermometers don't work outside of the lab? Fascinating.

[Sensei]

The whole reason I have been skeptical is because of the sheer level of emotional propaganda around global warming and little information about the science behind it.

Are you kidding?

 

Temperature change graph in the last 1000 years is not enough?

 

 

 

http://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_years

 

To calculate past temperature before invention of thermometer there are used f.e. tree rings . Read article.

http://en.wikipedia.org/wiki/Dendroclimatology

Edited August 14, 2014 by Sensei

[Essay]

...or maybe 20 thousand years would help your perspective.

 

 

...humans are a significant creator of greenhouse gasses. But, to conclude that human activity is significantly driving climate change seems, at best, an educated guess.

 

...very, very, well-educated guesses, which are then checked and tested and scrutinized and challenged and retested and validated, as with most science, medicine, and technology.

 

...and as with this overview of the information, published in Scientific American Magazine.

 

 

...Scientific American v.292, p.46 - 53 (2005) by William Ruddiman

GREENHOUSE EFFECT from human activities has warded off a glaciation that otherwise would have begun about 5,000 years ago. Early human agricultural activities produced enough greenhouse gases to offset most of the natural cooling trend during preindustrial times (yellow), warming the planet by an average of almost 0.8 degree Celsius. That early warming effect (a) rivals the 0.6 degree Celsius (b) warming measured in the past century of rapid industrialization (orange). Once most fossil fuels are depleted and the temperature rise caused by greenhouse gases peaks, the earth will cool toward the next glaciation–now thousands of years overdue.

http://www.nature.com/scientificamerican/journal/v292/n3/full/scientificamerican0305-46.html

 

...but it is just the orange and red parts that you might be worrying about, when you recognize how civilization just barely survived that (relatively stable) "actual trend," the yellow period.

...if you're the worrying type.

 

~

Edited August 14, 2014 by Essay

[Dekan]

Essay, that diagram is worrying. It seems to show that human activity is the only thing that's "warding off" a new glaciation, ie Ice Age. And that - if it weren't for our human activity - the world would today be in the grip of a new Ice-Age. Which would presumably bury most of Europe and North America under mile-thick sheets of ice. And destroy our present civilisation. And cause billions of people to die, not just in those continents, but worldwide.

 

Surely that wouldn't be a desirable situation! So, if a new Ice-Age is being kept away by human Global Warming, why should we want to stop the warming?

 

I mean, does it make sense to argue: "This man-made Global Warming is awful! It's not natural! So let's stop emitting greenhouse gases - get rid of that nasty industrial CO2 input into the atmosphere! Then the Earth will be able to cool down, resume its natural cycle, and give us a really great new Ice-Age by 2150"

 

Can't quite get it myself - does one have to be a dedicated "Environmentalist", to fully understand?

[timo]

I don't think your "Environmentalists" seriously want civilization to go back to a stage before early agriculture. Even if some people behave as if that was the actual intention of polar bear lovers.

[swansont]

Essay, that diagram is worrying. It seems to show that human activity is the only thing that's "warding off" a new glaciation, ie Ice Age. And that - if it weren't for our human activity - the world would today be in the grip of a new Ice-Age. Which would presumably bury most of Europe and North America under mile-thick sheets of ice. And destroy our present civilisation. And cause billions of people to die, not just in those continents, but worldwide.

 

Surely that wouldn't be a desirable situation! So, if a new Ice-Age is being kept away by human Global Warming, why should we want to stop the warming?

 

I mean, does it make sense to argue: "This man-made Global Warming is awful! It's not natural! So let's stop emitting greenhouse gases - get rid of that nasty industrial CO2 input into the atmosphere! Then the Earth will be able to cool down, resume its natural cycle, and give us a really great new Ice-Age by 2150"

 

Can't quite get it myself - does one have to be a dedicated "Environmentalist", to fully understand?

 

Burning all the straw in that argument would ward off a new ice age by at least a century. Can we discuss what real arguments are being used, instead of made-up ones?

[Dekan]

Well, the main argument seems to be this:

 

Do we let the Earth resume its natural cycle, and start a new Ice-Age, thereby freezing most of us to death.

 

Or do we do something about it, by pumping as much CO2 into the atmosphere as we can, to stabilize the Earth's climate at a warm temperature.

 

Simplicity is the key to solving complexity.

[swansont]

Well, the main argument seems to be this:

 

Do we let the Earth resume its natural cycle, and start a new Ice-Age, thereby freezing most of us to death.

 

Or do we do something about it, by pumping as much CO2 into the atmosphere as we can, to stabilize the Earth's climate at a warm temperature.

 

Simplicity is the key to solving complexity.

 

 

I'm challenging you to produce evidence of who is arguing we should resume the natural cycle, and also any mainstream climate scientist who thinks we need to pump CO2 into the atmosphere to stabilize the temperature, rather than the opposite.

[Essay]

Simplicity is the key to solving complexity.

It sounds as if you think huge doses of steroids would be fine, since small doses of steroids can be therapeutic; simplicity itself, right?

===

 

I’d agree we don’t want to return to ice-age conditions.

To intentionally lose 10,000 years of a relatively temperate climate, which still makes agriculture possible, would be fairly insane.

===

 

This level of GHGs seems to have offset the natural orbital (ice-age) cycle…

(but the above graph only records GHG levels up through “pre-industrial” levels)

 

…which gave us millennia of temperatures looking (fairly stable) like this; allowing civilization to survive:

 

 

So you can see how if the amount of GHGs (above) kept the climate level for thousands of years,

then you should also see we may not want to intentionally upset that balance now,

with those same emissions

 

…now shown up through 2005 (below).

These chemicals will force a larger difference, greater than between the ice age and today, which will change the climate.

 

I’d be skeptical of your suggestion that adding more GHGs

...to this already huge and rapid spike in GHGs

...will help maintain our relatively stable climate.

 

~

[Dekan]

 

 

I'm challenging you to produce evidence of who is arguing we should resume the natural cycle, and also any mainstream climate scientist who thinks we need to pump CO2 into the atmosphere to stabilize the temperature, rather than the opposite.

Thanks Swansont. On your first point - "who is arguing that we should resume the natural cycle". Isn't it the people who think we should reduce our artificial, industrially-generated carbon emissions?

If human-generated carbon emissions are regarded as "artificial", then it follows that they're "unnatural". And interfere with the natural cycle of the Earth. Including Ice-Ages.

 

So, if humans stop emitting lots of unnatural carbon, it will bring a return to the natural cycle - ie, recurrent Ice-Ages.

 

On your second point, about "mainstream climate scientists" - obviously they're only human. And most humans find it expedient to adjust views to the currently prevailing fashion. No slur intended - we all do it!

It sounds as if you think huge doses of steroids would be fine, since small doses of steroids can be therapeutic; simplicity itself, right?

===

 

I’d agree we don’t want to return to ice-age conditions.

To intentionally lose 10,000 years of a relatively temperate climate, which still makes agriculture possible, would be fairly insane.

===

 

This level of GHGs seems to have offset the natural orbital (ice-age) cycle…

(but the above graph only records GHG levels up through “pre-industrial” levels)

 

…which gave us millennia of temperatures looking (fairly stable) like this; allowing civilization to survive:

 

 

So you can see how if the amount of GHGs (above) kept the climate level for thousands of years,

then you should also see we may not want to intentionally upset that balance now,

with those same emissions

 

…now shown up through 2005 (below).

These chemicals will force a larger difference, greater than between the ice age and today, which will change the climate.

 

I’d be skeptical of your suggestion that adding more GHGs

...to this already huge and rapid spike in GHGs

...will help maintain our relatively stable climate.

 

~

Thanks Essay. I do appreciate the time and trouble you took to present the graphs and charts in your post. But they're quite complicated, and frankly I don't think I can interpret them well enough to offer a detailed reply.

 

I'm only looking at this subject from a simplistic viewpoint. Which involves answering these two questions:

 

1. Suppose we carry on emitting CO2 and other "greenhouse gasses" from our human industrial activities. Will that delay the onset of a new Ice-Age?

 

2. Suppose we cut back our CO2 emissions, or even eliminate them entirely. Will that speed up the onset of a new Ice-Age?

 

Thanks again for your post!

[swansont]

Thanks Swansont. On your first point - "who is arguing that we should resume the natural cycle". Isn't it the people who think we should reduce our artificial, industrially-generated carbon emissions?

If human-generated carbon emissions are regarded as "artificial", then it follows that they're "unnatural". And interfere with the natural cycle of the Earth. Including Ice-Ages.

 

So, if humans stop emitting lots of unnatural carbon, it will bring a return to the natural cycle - ie, recurrent Ice-Ages.

 

 

 

Aye, there's the rub. To go back to the natural cycle would require us to stop our emissions (and also grab a bunch of CO₂ out of the environment). You cite people who wish to reduce our emissions, but reduction and stoppage are not the same thing. And reduction doesn't get us to an ice age.

 

Who are the people who are calling for us to not just reduce (which is the actual position) but stop carbon emissions?

 

On your second point, about "mainstream climate scientists" - obviously they're only human. And most humans find it expedient to adjust views to the currently prevailing fashion. No slur intended - we all do it!

 

Intention or not, it's still a slur — an accusation that they hold a position only to go along with the crowd. In essence, that they are lazy and unprofessional. With no substantiation, of course. That's a tacit admission that you have nothing here, except to sling mud or perhaps something that looks like mud.

[Dekan]

Thanks Swansont. In reply to your # 21:

 

1. You quibble about the distinction between "stopping" carbon emissions, and "reducing" them. The problem is this: Suppose carbon emissions are regarded as bad. Then, by how much should they be "reduced", until we're sure the badness has gone? Will a 50% reduction be enough? Or 25%, or 10%, or what? How can we know? We can't. The only way to be sure, is to stop them altogether. Which is what I think, some Environmentalists are really aiming at. (BTW, this reminds me of discussions in theological contexts, about how far "interest rates" must be reduced so as not to constitute "usury", but that's another story!)

 

2. I wasn't accusing anyone of being "lazy or unprofessional" Those are your words, not mine! But everyone has their career to think about. It's not good to risk it, by expressing "wrong" opinions.

[swansont]

Thanks Swansont. In reply to your # 21:

 

1. You quibble about the distinction between "stopping" carbon emissions, and "reducing" them. The problem is this: Suppose carbon emissions are regarded as bad. Then, by how much should they be "reduced", until we're sure the badness has gone? Will a 50% reduction be enough? Or 25%, or 10%, or what? How can we know? We can't. The only way to be sure, is to stop them altogether. Which is what I think, some Environmentalists are really aiming at. (BTW, this reminds me of discussions in theological contexts, about how far "interest rates" must be reduced so as not to constitute "usury", but that's another story!)

How can we know? It's called science.

 

Characterizing this as a quibble points to a sloppiness that makes for bad science. We quantify things in science. Stopping vs reducing is a significant distinction, not a small one.

 

 

2. I wasn't accusing anyone of being "lazy or unprofessional" Those are your words, not mine! But everyone has their career to think about. It's not good to risk it, by expressing "wrong" opinions.

 

You were projecting motivation onto others, and recent evidence indicates you're bad at it. You've pretty much struck out in your characterization of scientists and gotten in backwards. The best way to advance your career is by doing good science. Bad science is eventually shown to be just that. People whose work is discredited usually leave the field.