Actual Carbon Emissions vs. IPCC Scenarios - how far away is safety?

[GliderGuider]

I've been learning a lot about the IPCC emissions scenarios over the last couple of days. Just for grins I decided to do the plot below. It compares two IPCC scenarios against our actual global emissions from fossil fuels.

The scenarios I chose were:
A1T, which ends up with the world at +2 to +3 degrees Celsius in 2100; and
A1FI (FI stands for "Fossil Intensive&quot , which puts the world at +4 to +5 degrees C in 2100.

I plot our actual carbon emissions in red, and fit a polynomial trend line out to 2100. This is the "real" BAU scenario, so far.



I'm not saying we'll get to 80 GtC per annum in 2100, I'm just using the comparison to point out how much correction we would need to do to get back down to a level that's merely extremely dangerous, let alone getting back to one that may (or may not) be reasonably safe.

Note that we are already above the emissions of both IPCC scenarios for 1990, 2000 and 2010 - and the gap is growing as expected.

The actual data is from the BP Statistical Review, the IPCC data is from the IPCC AR4.

[AverageJoe90]

1. You may want to redo this at some point.

80 GtC of coal by 2100? We'd have run out of all fossil fuels long before then. I do suggest you redo this if you want to make a good comparison.

[GliderGuider]

2. This is the curve that Bill McKibben's "Do the Math" tour is all about.

http://math.350.org/

According to McKibben's numbers, we have enough fossil fuel (2795 GtC) to last until about 2090 on my projection.
And, if we accept McKibben's number of 565 GtC as the maximum safe amount we can emit, we'll hit that around 2040.

There are only two things that I can see that might interfere with that course of events. One is the declining EROEI of fossil fuels (especially oil), and the other is the collapse of the globalized industrial economy (and a little bit later, civilization itself) due to a combination of rising fossil fuel EROEI and rising planetary temperature.

We are unlikely to see renewables magically slow that curve, no matter how well (or not) Germany is doing at that. It would take too long for the replacement to kick in, the number of nations involved is too large, and their self-interest is too strong - as long as the fossil fuels are affordable and offer an EROEI over about 5:1 we will burn them. According to a recent draft paper I've seen by Charles Hall, 5:1 is well below the level necessary to maintain what we think of as a "modern" civilization - he now pegs that at around 14:1.

In any event, we are now committed to +2C of warming, and as Kevin Anderson of Tyndall Cenre warns us, +2 is merely a transition point on the path to +4C. Which means we will see +4, probably by mid-century. Given that what we're now seeing at +0.8C is what we recently expected to see at +2, the world at +4 is likely to resemble the world we hadn't planned on until +5 or +6. Here is what RealClimate says about that, in a review of Mark Lynas' book "Six Degrees: Our Future on a Hotter Planet":

http://www.realclimate.org/index.php/archives/2007/11/six-degrees/

At 5° and 6°, the book really does start to sound alarmist, with the analogy to Dante’s Inferno – used to good literary effect throughout the book – coming very much to the fore. At five degrees, we have “an entirely new planet is coming into being – one largely unrecognizable from the Earth we know today. At six degrees, “… the pump is primed … not for flourishing palm trees in Alaska, but for the worst of all earthly outcomes: mass extinction.”

Aha, say the skeptics! It is alarmist after all. But is it? Lynas’s reference to the “entirely different planet” actually refers to the fact that at five degrees, the “remaining ice sheets are eventually eliminated from both poles.” That’s entirely true. And unlike in Gore’s discussion of sea level in Inconvenient Truth Lynas does emphasize the long timescales (thousands of years) in this case. Furthermore, there is published research that raises the likelihood of the significant loss of ice sheets at lower temperatures, and Lynas could have claimed certainty of a disappearing Greenland ice sheet in an earlier chapter. That he doesn’t do that is characteristic of the book: it doesn’t tend to go beyond the published literature. This is what Lynas claims at the outset — “all of the material in the book comes from the peer-reviewed scientific literature” – and I think he does an admirable job.

And that brings us back to the question I promised to raise at the beginning, which is this:

If a reading of the published scientific literature paints such a frightening picture of the future as Six Degrees suggests – even while it honestly represents that literature – then are we being too provocative in the way we write our scientific papers? Or are we being too cautious in the way we talk about the implications of the results?

Extinction. It's not just McPherson and me saying stuff like this.

[wtmusic]

5. Six Degrees and The God Species should be required reading for policy makers

Mark Lynas is a self-taught scientist, but his work is not disputed by the best climatologists in the world.

If 1/2 of his predictions are true we're in trouble.

[cprise]

8. To what extent do you think we could trigger another Permian extinction?

Dr. Peter Ward has written about how the greatest extinction of all time was triggered by global warming roughly 200m years ago. His description of the devastation seems to hinge on the encroachment of anoxic bacteria in the oceans and how it eventually produced so much H2S gas that the sky turned green (his book on the subject is titled "Under A Green Sky"). The gas is supposed to have killed off a very large proportion of the plants and animals that were otherwise coping with the hotter conditions.

I can't imagine humanity surviving such an event.

Since that past episode of global warming was itself triggered by a surge in volcanism (creating the Siberian traps) I wonder if one significant difference between then and now would be presence of sulfur that the volcanoes/calderas probably added to the biosphere.

[GliderGuider]

16. I have Ward's book - it's a terrifying read...

I don't think we could trigger that sort of event - it would probably take continental-scale vulcanism, and as narsty as humans are to the planet I don't think we can quite do that.

However, I think a smaller-scale extinction combining the best features of both PETM (for the oceans) and the K-T event (for us land-based critters) might be doable. If we manage to burn through say 2,000 GtC before the end of the century, and trigger a bunch of methane cascades in the process, it should be possible.

I'd give it a POMA probability of 10%, but only sometime in the 22nd century. Of course an event like that would have some foreshocks, one of which we're seeing around us now, but those should ramp up in intensity by the end of the century. Humans won't be at risk - at least not the whole species, though the implosion of this cycle of civilization might make some of us want to participate...

[cprise]

34. The projections I have seen put us at over 900ppm CO2 by 2100

Would you disagree that is our worst-case scenario?

That is right in the same ballpark as the estimated level which triggered the Permian extinction.

[GliderGuider]

35. I think our worst-case scenario (at the moment) is 1200 ppm by 2100.

I'm working on a post about this right now, but the short answer is that based on the pattern of our last 20 to 30 years of fossil use, we will hit 1000 to 1200 ppm by 2100. There is enough unburned carbon to do it.

The worst news is about global surface temperatures. Depending on how sensitive the climate actually turns out to be, we could be well over +10 by 2100. At a sensitivity of +3C per doubling, the range would be 8 to 10, if it's +5 per doubling the range will be 13 to 18 degrees C.

So we're looking at 1000 to 1200 ppm, for a temperature range of +8 to +18 (!!!) by 2100.

Now that's what I call a worst-case scenario. I'll post an OP with graphs and explanations tomorrow.

[cprise]

40. That seems too hot to avoid a drastic change in biochemistry

I don't see how anaerobic microorganisms could not take over the oceans under such conditions. Again, my point about H2S.

[AverageJoe90]

12. Mostly true, but there's a difference:

McPherson & Light and those like them are saying that HUMAN extinction & and that of ALL other life is practically inevitable. Anderson doesn't say that humans will go extinct or that a mass extinction is inevitable. That's a key difference, IMHO.

[cprise]

14. There are a number of species that lived through that level of warming

...in the past. Humanity is not one of them. We are not even remotely adapted for such conditions.

So then what could mitigate that? High technology? It is usually assumed by people examining the worst-case scenarios that industrial civilization will be hobbled or obliterated. That means we'd have to get through 50,000 years or more with low tech or no tech. In conditions we never adapted to. Even fairly distant cousins on our evolutionary branch never adapted to the hothouse climate.

Anyone ruling-out human extinction would have to do so on the assumption that industrial civilization stays intact even during the worst climate repercussions.

Now that is a stretch.

[AverageJoe90]

15. What honestly makes you think we can't?

You really oughta give our fellows a little more credit, cprise. I have, from time to time, brought up the Toba eruption as an example. Why? Because, the effects of said event where not only sudden and without warning, but also more acute. It may be true that only about 100,000 of our ancestors survived, out of millions, mainly because of the aforementioned factors, and others, but we did survive. Even the worst case scenario of global warming wouldn't be at all likely to reduce our numbers to one half of a percent of what they once were, even half a millenium from now, let alone just a century.

It is usually assumed by people examining the worst-case scenarios that industrial civilization will be hobbled or obliterated.

Which may happen, especially the former.

That means we'd have to get through 50,000 years or more with low tech or no tech.

Now that's a real stretch. 50,000? C'mon man, even Mad Max can't top that.

Anyone ruling-out human extinction would have to do so on the assumption that industrial civilization stays intact even during the worst climate repercussions.

No, and in fact, anyone who thinks that human extinction is even close to inevitable would have to operate on a number of outlandish assumptions, including the belief that humans are unable to adapt to change when needed. If this was even partly true, then none of us might be here today.

I do hate to say this, but your opinions as expressed here are kinda similar to operating on faith, just in the opposite direction.

I have no doubt that humanity will face a rocky road in the decades and centuries to come, but I do try to be realistic.

[GliderGuider]

23. It's actually not a compliment to the species that we survived Toba.

There are two reasons for that.

The first is that Toba wasn't a large-scale extinction event. If very few other species died out, it's no great miracle that we survived. There was nothing special about us that would have enabled us to survive where few others perished. Claiming there was amounts to bravado.

The second is that there is some serious question as to whether there was even a bottleneck. Some paleontologists assert that our population was very low to begin with, was not reduced much if at all by the event, and simply underwent a bit of a population explosion in the tens of millennia afterwards:

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

The work done on Neanderthal sequencing (Green 2007) has identified little evidence of Neanderthal contribution to humans, moreover it describes an effective size of the population when humans and Neanderthals split was about 3000 individuals. Taken in the light of Schaffner's and Takahata's effective populations sizes, 3000 < Ne, female < 6000 and 2000 < Ne, male < 4000 does not appear to represent a magnitude shift downward from the average size. Taking a null hypothesis, prior to and after the mtDNA MRCA population sizes appear to reflect long-term small population structure up until 70,000~150,000 years ago, not a brief constricting bottleneck, but a long period of constrained size followed by an expansion.

It doesn't seem to me that Toba provides much evidence of human exceptionalism.

If we were to actually trigger a true extinction event like PETM, we should expect humans to be as subject to it as any other species.

[AverageJoe90]

25. Well, I'm now convinced that more research is needed re: Toba at any rate.

The second is that there is some serious question as to whether there was even a bottleneck. Some paleontologists assert that our population was very low to begin with, was not reduced much if at all by the event, and simply underwent a bit of a population explosion in the tens of millennia afterwards:

Well, they'd be dead wrong as most paleontologists agree that there was a bottleneck(although Toba may not have been the only cause, according to some.), according to most evidence we have right now(not to mention that small populations breeding amongst almost always lead to humongous genetic issues down the road, so human populations can't have been as low as 3,000, either, it just isn't doable. Some species have would have trouble thriving at all with greater numbers.)

If very few other species died out, it's no great miracle that we survived.

Somehow it seems that more research is likely needed in this area; Yellowstone is a volcanic complex of similar potential and the majority of scientists I've heard talk about this say that there's a damn good chance it's eruption very well could cause a mass extinction. And if Toba really, truly didn't cause a significant extinction, which can be plausibly argued is pretty doubtful, given the research done on the possible effects of a future eruption of the Wyoming complex, then Earth miraculously dodged one hell of a bullet, and the next time a supervolcano erupts, this planet may not be so fortunate; after all, it was a supervolcano in today's Siberia that was (likely) the primary (though not only, recent research seems to suggest.) cause of a mass extinction which wiped out ~90% of marine species and about 2/3rds of terrestrial life.

If we were to actually trigger a true extinction event like PETM, we should expect humans to be as subject to it as any other species.

I'm not terribly convinced methane releases on the level of PETM would be possible, either. Could it happen? Yes. Could it lead to devastation of much life on Earth were this to happen? Yes, I think so. But so far, I've seen no convincing evidence of any plausible event quite on the scale of PETM.

[cprise]

33. I briefly told you what

As for your "realism", putting Toba on a par with worst-case AGW doesn't fly.

I do hate to say this, but your opinions as expressed here are kinda similar to operating on faith, just in the opposite direction.

My faith in humanity is based on our potential for good, on what could be-- It isn't blinkered to disregard the depths to which we are capable of sinking.

OTOH you do not seem to accept that the worst-case scenarios are possible at all. Worse still, that denial emanates from your sense of political realism.

I've seen you mention the Precautionary Principle but I don't think you quite know what it entails: The higher the stakes involved, the greater the imperative to guard against less-likely scenarios.

[AverageJoe90]

36. I don't think you've really understood what I've been trying to say.

It isn't blinkered to disregard the depths to which we are capable of sinking.

Me neither. But I'm not so blinkered as to think that human extinction is really inevitable, or even really possible because of AGW alone, as some may believe, either.

My faith in humanity is based on our potential for good, on what could be--

Forgive me, but I haven't really seen that from you all that much.

OTOH you do not seem to accept that the worst-case scenarios are possible at all.

On the contrary, I've said over and over again that the worst case IS indeed possible; maybe not as likely as some may assume but still possible.

The higher the stakes involved, the greater the imperative to guard against less-likely scenarios.

Yes, but the thing is, I've never once disagreed with that.

[cprise]

39. What a bunch of sloppy posturing

I don't have to sign up with your exceptionalist denialism in order to have hope. Go ahead and elide possibility with inevitability to make your "point". But don't think that people won't notice; You are at odds with many here in pushing your idea of what is politically acceptable like some 1950s consensus of nuclear war.

Humans are adapted to surviving ice ages, not hothouses, and the projected warming will be too quick for us to physiologically adapt-- those are facts. With so much other life perishing from under us, we would have to acknowledge the possibility of our own demise. We are not so different from other animals that we can count on escaping all of the unintended consequences where they do not.

As such, the Precautionary Principle places the burden of proof with those who insist on ruling out human extinction.

[AverageJoe90]

41. Sure, sure.

And Joe Biden is the Easter Bunny......

I don't have to sign up with your exceptionalist denialism in order to have hope.

What denialism? Have you actually seen what real ACC deniers say? They don't acknowledge ANY of the science concerning global warming.

I, however, acknowledge that:

1.)The planet is warming, and that human activities are almost certainly the primary factor.

2.)There are many risks associated with said warming.

3.)That action should be taken to mitigate the problem.

4.)If we do nothing, the risk severely crippling the environment, civilization, and all life on Earth is much greater than with action.

Denialist? Not in the least.

But don't think that people won't notice; You are at odds with many here in pushing your idea of what is politically acceptable like some 1950s consensus of nuclear war.

That is simply untrue.

and the projected warming will be too quick for us to physiologically adapt-- those are facts.

No, it's conjecture and nothing more. You seem to assume that humans are just like any other creature on Earth. But you'd be wrong.

With so much other life perishing from under us, we would have to acknowledge the possibility of our own demise. We are not so different from other animals that we can count on escaping all of the unintended consequences where they do not.

We can certainly escape extinction. Now, I don't know about surviving in today's numbers; I would imagine that it's possible that climate change, and all of it's direct & indirect effects, as well as wars, disease, etc. could perhaps lead, or at least contribute, to a significant culling of the population(I doubt that CC alone wouldn't be enough to cause multi-billion death tolls on its own but wars, civil strife, and epidemics, etc. over time, could in fact, make up for that).

We, at least, have the capability to survive, when many other creatures might not. I believe it's called "Survival of the Fittest".

As such, the Precautionary Principle places the burden of proof with those who insist on ruling out human extinction.

The end of post-WWII civilization as we've come to know it? Yes. The possibility that climate change alone could create hundreds of millions of refugees? Yes. Human extinction? No. Human extinction just isn't possible thru CC alone.

[NoOneMan]

6. We probably run out of life as well before then

Which is kind of the point.

Off topic, do you think Anderson is being an extreme alarmist in the video/ppt that GG has recently posted a link to? I wasn't sure if you responded to that yet, as he seems to completely discredit the entire basis of the +2C models you've expressed hope in.

[AverageJoe90]

9. Haven't gotten to it just yet.

But to be honest, as I've stated many times before, even the worst case scenario of +6*C wouldn't lead to the extinction of humanity, and certainly not all other life either. And yes, that is a fact, by the way.

[NoOneMan]

11. It would surely be the end of civilization as we know it

Please listen to it. Very informative. Takes about an hour.

Humanity would be almost unrecognizable, and undoubtably, billions would die from food production problems alone. Logistical issues could kill billions more from a lack of ability to organize and distribute goods in such a world.

[XemaSab]

13. You keep using that word "fact,"

I do not think it means what you think it means.

[AverageJoe90]

17. I know full well what I'm talking about here.

Yes, it is indeed a fact that global warming, while it could prove to be a rather tragic setback for us all, would not necessarily lead to our extinction. And the fact is, we really have lived thru worse; Toba wiped out all but around half a percent of humanity 72k years ago, and mainly because of the swift & acute nature of the disaster that unfolded. As bad as things could get, we're at least fortunate in the respect that very much unlike a supervolcanic eruption, there is indeed the chance to do something about AGW.

[XemaSab]

18. That's not what you said

But to be honest, as I've stated many times before, even the worst case scenario of +6*C wouldn't lead to the extinction of humanity, and certainly not all other life either. And yes, that is a fact, by the way.

versus

Yes, it is indeed a fact that global warming, while it could prove to be a rather tragic setback for us all, would not necessarily lead to our extinction.

These two statements do not mean the same thing, yet they both abuse the word "fact."

[AverageJoe90]

19. OK, I do realize I could have been clearer. However, my point does still stand.

My apologies. But how am I abusing the word?

Again, let's look at past disasters. Humanity is not invincible, true, but you gotta admit we're a pretty hardy lot when the going gets tough, even if not everybody makes it.
To say human extinction is inevitable, or even close to it, because of global warming alone, as some have said in the past(such as Malcolm Light, for example, if you remember the controversy behind his "all life extinct by mid-century" article back in the summer of this year.), is not only an article of faith, or at least similar to it, but totally unprovable as well.
It can be legitimately argued that we can't safely predict humanity's future beyond, say, a century or two or so, in any direction, that is true, but we can look back at past events of similar magnitude as well as the science, and while the science does say that there could be serious trouble ahead, especially if we do nothing to act, it does not say, by any means, OTOH, that human extinction is inevitable, or even any sort of likely, and certainly not so within our lifetimes or those of the next generation or two immediately ahead of us.

[XemaSab]

20. The stuff coming out of your keyboard

is the kind of hubris that got us here in the first place.

[AverageJoe90]

21. On the contrary.

This is the kind of thing that will save our bacon in the end: Getting people to realize that a major problem exists while not overdosing on the doom-and-gloom(while, at the same time. not discounting the possibility that the worst case scenarios could indeed happen) really is one of the best solutions out there.

Hey, if you want me to admit one thing, I'll be glad to: the excess optimism of 20-30 years ago didn't work all that well. But neither will the levels of pessimism emanating from the mouths of people like McPherson & Light and those like them, no matter how noble their intentions may be.

It's a good part of the reason why I stick to sources like SkepticalScience, and Pete Sinclair, our very own GreenMan: They lay out the truth of the matter without excessive amounts of doom-and-gloom or rose-colored optimism. We need more people like them; most people who read the E & E forums would probably agree with me at least on that.

[caraher]

3. I'll go with the IPCC scenarios

All your trendline shows is that if there were some reason to suspect that an n-th order polynomial were the correct model for future emissions, the red curve is the polynomial of that order that best fits whatever span of recent data you have. You could also fit any number of other mathematical functions to the same data, get "good" R^2 values, and have a wildly different curve.

[GliderGuider]

4. That's your prerogative - this thumbnail assessment isn't the Truth.

I agree that other curves could be fitted. However, in order to have a chance to escape a +4C hell, we're probably limited to looking at sigmoid/logistic curves with some sort of built-in saturation effect. Do human needs for energy saturate? There are external events that can suppress them, but I don't know of any organic reason why that should be so. Energy use and CO2 emissions have grown at a faster rate than population for the last 100 years, which is a good indication that the curve is open-ended.

See this post for my look at open-ended, super-linear scaling.

Human population growth does in fact appear to be following a sigmoid curve (even though it's going to saturate too late for comfort), but the growth of energy and CO2 does not. That's worrying, because if it doesn't stop rising on its own we will depend on external forces like political policy-making to modify its trajectory. Or just wait for events to modify it for us.

Anyway, the main point of this graph was to show that we would not necessarily "run out of" fossil fuels before we hit extremely dangerous climate territory, and that the possibilities definitely include us blowing well past even the most pessimistic IPCC scenario.

[AverageJoe90]

10. Very true.

Even so, I think the Precautionary Principle really should be considered. +6*C may not necessarily occur even in the worst case scenario of business as usual, but is it a gamble really worth taking? I think pretty much everyone can agree that it isn't, by any means.

[OKIsItJustMe]

22. I'm unwilling to extrapolate out to 2100, based soley on data for the past 20-odd years

Zoom in on the trend from 1990 to 2015. Label A1F1 “IPCC ‘Worst Case’ Scenario” and I think the message comes across loud and clear.

[GliderGuider]

24. Stopping the extrapolation at 2015 leaves far too much wiggle room for the diminishers.

They can always claim that the divergence of our actual emissions from the A1FI scenario is not too great, that the curves in that time frame are basically similar, and so the gap could be closed in a decade or two following 2015.

Running out the curves for a few decades makes it clear that there are fundamentally different forces driving the two cases. It also plants the idea that it might take more than a snap of the fingers and some windmills to align ourselves with the IPCC - even with their worst case +4C scenario. And since the temperatures are given for the end of the century, it helps to think about what our situation couldl probably be like at that point.

Now, there is a lot of variability in the projection, especially depending on the chosen starting point. I started at 1990, and got emissions of 80 GtC in 2100. If I start at 1980 I get 60 GtC in 2100, and starting at 1985 gives me 70, using the same class of curves. What this indicates to me, beyond the prosaic ±15% variation, is that the emissions curve is growing steeper with time. Metaphorically, we have our carbon legs under us and are sprinting for home. Looking out to 2100 in that context makes even more sense to me.

[OKIsItJustMe]

29. That’s worse!

You chose 1990 rather than 1980 or 1985, because that gave you a worse result.

This is the sort of game that the “skeptics” like to play, choosing their starting points to produce a result they like.

It’s also the sort of game that some proponents of solar and wind like to play, suggesting that an apparent geometric increase extending over a few years will continue indefinitely.
http://re.jrc.ec.europa.eu/refsys/pdf/PV%20reports/PV%20Status%20Report%202012.pdf

[font face=Serif][font size=3]
Fig. 1: World PV Cell/Module Production from 2000 to 2011
[/font][/font]

(It would be wonderful if it did, but such a trend is virtually impossible to maintain indefinitely.)


However, I think it’s reasonable to assume that as we use more and more of our fossil fuel reserves, fossil fuels will continue to become more and more expensive. As a result we will use less of them.

I like to point out to people that we didn't just discover oil in the tar sands of Canada or have some technological breakthrough. Why are we doing it now then? Because the easiest stuff to get to is (essentially) gone. So, now, we’re going after the harder stuff, even though it’s more expensive to produce. The cost of fossil fuels has finally risen high enough to make “unconventional” sources like tar sands, deep ocean drilling & high volume horizontal hydraulic fracturing profitable.

At the same time as fossil fuels are becoming more and more expensive, the cost of renewable energy is coming down. Whether people believe in anthropogenic climate change or not, financially, they will be driven to pursue alternative energy sources, which will increasingly be renewables.

So, I simply don’t believe that smoothly increasing emissions curve is real.

[GliderGuider]

30. The point is to present what is possibly the worst case scenario imaginable.

And to make the point that it's based entirely on our current behaviour. The point of this is to shock people, not to give them hope.

Yes, our behaviour will change as circumstances change, as it always does.

the point is that we have no way of knowing at this point how circumstances will change, so rather than get into that bunfight I present the consequences of our demonstrated current behaviour. Think of it as a baseline. The main point is to show just how far our baseline is from what the behaviour necessary to meet even a minimally effective IPCC scenario.

I'm working on a new set of graphs that will incorporate three starting points for emissions (1980, 1985 and 1990) and show the ultimate CO2 and temperature consequences for each. Watch this space.

[OKIsItJustMe]

31. I suggest a simple graph for 1980-2015

That should be shocking enough.

Or, do some curve fitting on that solar production graph, and extrapolate that out to 2100. (It will be equally valid.)

[GliderGuider]

32. I prefer to keep it in line with the IPCC projections that go out to 2100.

Trust me, a graph to 2015 will not be nearly shocking enough.

[AverageJoe90]

26. Me neither.

Nobody doubts that carbon emissions are growing(which is not at all a good thing, as most will agree!), but 80 GtC by 2100? I doubt we even have a twentieth of that to burn.

[GliderGuider]

27. You don't trust Bill McKibben?

According to McKibben's numbers, we have enough fossil fuel (2795 GtC) to last until about 2090 on my projection.

Global Warming's Terrifying New Math

This number is the scariest of all – one that, for the first time, meshes the political and scientific dimensions of our dilemma. It was highlighted last summer by the Carbon Tracker Initiative, a team of London financial analysts and environmentalists who published a report in an effort to educate investors about the possible risks that climate change poses to their stock portfolios. The number describes the amount of carbon already contained in the proven coal and oil and gas reserves of the fossil-fuel companies, and the countries (think Venezuela or Kuwait) that act like fossil-fuel companies. In short, it's the fossil fuel we're currently planning to burn. And the key point is that this new number – 2,795 – is higher than 565. Five times higher.

The Carbon Tracker Initiative – led by James Leaton, an environmentalist who served as an adviser at the accounting giant PricewaterhouseCoopers – combed through proprietary databases to figure out how much oil, gas and coal the world's major energy companies hold in reserve. The numbers aren't perfect – they don't fully reflect the recent surge in unconventional energy sources like shale gas, and they don't accurately reflect coal reserves, which are subject to less stringent reporting requirements than oil and gas. But for the biggest companies, the figures are quite exact: If you burned everything in the inventories of Russia's Lukoil and America's ExxonMobil, for instance, which lead the list of oil and gas companies, each would release more than 40 gigatons of carbon dioxide into the atmosphere.

The question is not whether the fuel is available. It most assuredly is, at least till 2090 or so on that projection and even longer if the curve is lower. The questions are: will we be able to substitute carbon-free energy to a sufficient scale to make burning it unnecessary and economically unattractive, and whether or not other events - like a widespread socioeconomic disintegration of some sort, perhaps due to rapid climate change - will make burning it impossible. I say the answer to the first question is,"No, we won't," and the answer to the second is, "Quite probably."

Can I ask what you base your doubts on?

[AverageJoe90]

28. It seems I made a mistake. I apologize.

I guess I'd forgotten about the McKibben piece for the moment. So I'll take back what I said.

[caraher]

37. On the lighter side...

An extreme case of why one cannot pick functions out of a hat and conclude much from extrapolating them, even if the fit to data is perfect.

[GliderGuider]

38. Yer not going to like my next trick very much either, then.

I hope you'll give the idea a chance, though.