Global Warming/Climate Change Discussion Thread

[Touring Mars]

I wonder if there isn't a decrease in the last 20,000 years that occurred with the same rate of the increase we're seeing now. Certainly some of the early 1900's data indicates that fast changes can occur.

I think what your plot shows is that the temperature fluctuations that we've seen even in the last 150 years are not so unusual or out of family of what is plausible naturally.

I should correct myself here - the PNAS paper seems to say that rate of increase in anthropogenic forcings during the 20th Century is unprecedented in the context of the last 20,000 years - and that the current rate of change (increase) may be as high as the rate of change of natural forcings during any 40 year period during the last 1000 years.

So, the temperature change observed over the 20th Century may not be without precedent after all, but the cause of the change is... that said, the predicted effect of these rapidly increasing forcings is that the change in temperature in the next 100 years will be as high as natural forcings have produced (alone) in the last 1000 years...

 

[Danoff]

So, the temperature change observed over the 20th Century may not be without precedent after all, but the cause of the change is...

But I thought part of the reason we were so certain of the cause was the unprecedented nature of the change. Take away the lack of precedent (that's a few negatives for you), and shouldn't that cast some doubt on the cause?

 

[Sureboss]

One thing for sure is the world will never 100% agree on the cause. People will always doubt it, if we work on the basis that we are causing the problem, then we will struggle to make the demands required to slow down/erradicate the problem. I think that the likeliest possibility is that a pandemic will reduce our huge population (Note: The 3rd world countries have the biggest growing populations anyway and they will most likely suffer the biggest damages). Nature has a way of sorting itself out, if it needs to, it will, imo.

 

[Touring Mars]

But I thought part of the reason we were so certain of the cause was the unprecedented nature of the change. Take away the lack of precedent (that's a few negatives for you), and shouldn't that cast some doubt on the cause?

Depends what we're saying is unprecedented - certainly the rate of change of anthropogenic forcing is unprecedented, and the fact that anthropogenic forcings are now as significant a factor in global climate change as all natural forcings have been in the past 1000 years is also unprecedented.

we will struggle to make the demands required to slow down/erradicate the problem.

This is for definite. Although I think that mankind could do something, I'm of the opinion that we won't.

Nature has a way of sorting itself out, if it needs to, it will, imo.

True - but let's not forget that Nature is also indiscriminate and totally indifferent to the plight of mankind.

 

[Sureboss]

The changes would be too drastic, people would fight it and you'd have huge unrest in most countries.

We've been doing this in Science and it amazes me how the developed countries population hasn't changed much since WWII but it's been the underdeveloped countries that have the huge and growing populations. Big families, etc. Whereas a hundred years ago maybe 2/3 of a 12 children family may survive in say Bangladesh, now due to the medicinal advances it's now 8/9. Population has tripled in 60 odd years. And it'll be the countries like Bangladesh, China, India where the 'pandemic' will hit the most, as we've seen with the few but deadly 'outbreaks' of H5N1.

Something has to give and it won't be nature.

 

[Danoff]

Depends what we're saying is unprecedented - certainly the rate of change of anthropogenic forcing is unprecedented, and the fact that anthropogenic forcings are now as significant a factor in global climate change as all natural forcings have been in the past 1000 years is also unprecedented.

How do you know? How can you be sure if we can't point to something unprecedented happening with temperature? These guys are pretty confused about how to model even basic stuff - like clouds, for example. They don't know if clouds actually heat or cool the earth. How can we have the influence of human behavior on temperature down to a tenth of a microdegree if we don't even know how clouds work?

 

[Touring Mars]

How do you know? How can you be sure if we can't point to something unprecedented happening with temperature? These guys are pretty confused about how to model even basic stuff - like clouds, for example. They don't know if clouds actually heat or cool the earth. How can we have the influence of human behavior on temperature down to a tenth of a microdegree if we don't even know how clouds work?

How can I be sure about what? That the rise in anthropogenic forcing during the 20th Century occured faster than changes in the combined radiative forcing from CO2, CH4, and N2O during the past 20,000 years? The evidence is pretty clear on that. That global temperatures increased ten times faster in the 20th Century than in the period since the Last Glacial Maximum? That's true as well...

 

[Danoff]

How can I be sure about what? That the rise in anthropogenic forcing during the 20th Century occured faster than changes in the combined radiative forcing from CO2, CH4, and N2O during the past 20,000 years? The evidence is pretty clear on that.

I'll grant you that anthropogenic forcing is probably changing faster than ever. But where is the evidence that it's actually having a substantial impact on the environment?

That global temperatures increased ten times faster in the 20th Century than in the period since the Last Glacial Maximum? That's true as well...

We talked about this just a few posts back. I thought it concluded when you said:

So, the temperature change observed over the 20th Century may not be without precedent after all, but the cause of the change is

Ok, actually, scratch everything I wrote above. This is the real problem I have:

the fact that anthropogenic forcings are now as significant a factor in global climate change as all natural forcings have been in the past 1000 years is also unprecedented.

How do you know this? If you stop and think about it, it's actually almost impossible to believe - that somehow mankind is having as much of an effect as any natural phenomenon in the last 1000 years??? Surely that's not what you think.

 

[Touring Mars]

Anthropogenic forcings are now as significant a factor in global climate change as all natural forcings have been in the past 1000 years

How do you know this?

I'm just repeating what was published in PNAS last week - strictly speaking I don't 'know' it... but the evidence presented in that paper says that "(GHG gas) forcing(s) are several times larger during the Industrial Era than the last 2,000 years"...obviously, from 0-1750 A.D., there was effectively no significant anthropogenic GHG emissions to speak of, and so this time period can be considered as exemplary of natural forcings alone. Only in the modern era, 1750-2008, are we seeing the rate of change in radiative forcing increasing rapidly.

If you stop and think about it, it's actually almost impossible to believe - that somehow mankind is having as much of an effect as any natural phenomenon in the last 1000 years??? Surely that's not what you think.

It's almost impossible to believe life could have evolved too, but it did... belief doesn't enter into it for me. I don't see how it is so implausible... what we can see from the current evidence (as the paper in PNAS goes into in some detail), is that naturally occuring radiative forcing due to GHGs in the past 20,000 years have not produced a warming effect anything like that observed in the last 100 years - a period in which human GHG emissions have added to the total GHG concentrations in the atmosphere to their highest point in 650,000 years... I don't see what is so implausibe about it. What you seem to be suggesting is that no amount of human GHG emissions could affect the global climate, even in theory. I don't agree with that...

Let's not forget, too, that human GHG emissions are only one type of anthropogenic forcing. Deforestation and anthropogenic desertification are also factors operating on a globally significant scale...

 

[Danoff]

I'm just repeating what was published in PNAS last week - strictly speaking I don't 'know' it... but the evidence presented in that paper says that "(GHG gas) forcing(s) are several times larger during the Industrial Era than the last 2,000 years"...obviously, from 0-1750 A.D., there was effectively no significant anthropogenic GHG emissions to speak of, and so this time period can be considered as exemplary of natural forcings alone. Only in the modern era, 1750-2008, are we seeing the rate of change in radiative forcing increasing rapidly.

Identifying exactly how much of a role GHGs are playing is the trick. It's not a trick I'm convinced they have down yet.

It's almost impossible to believe life could have evolved too, but it did... belief doesn't enter into it for me.

Aw comeon. Surely you know me better than that by now. I'm using a colloquial definition of "believe", and what I mean by "almost impossible" is that it's a silly claim - that somehow man has now eclipsed nature in terms of our influence on the temperature. Afterall, what we're seeing is tiny fluctuations compared to the absolute value (in Kelvin). Nature still has far and away more to do with our temperature than we do.

I don't see how it is so implausible... what we can see from the current evidence (as the paper in PNAS goes into in some detail), is that naturally occuring radiative forcing due to GHGs in the past 20,000 years have not produced a warming effect anything like that observed in the last 100 years

So maybe it's not due to GHGs. But GHGs seems to be the automatic conclusion.

What you seem to be suggesting is that no amount of human GHG emissions could affect the global climate, even in theory. I don't agree with that...

I don't either. I think probably ANY GHG emissions affect the global climate. Even breathing. <- That's not sarcastic. My question is "how much". And I'm not convinced by a long shot that we're now the driving force behind our climate.

 

[Touring Mars]

Identifying exactly how much of a role GHGs are playing is the trick. It's not a trick I'm convinced they have down yet.

True - plenty of uncertainty remains, but in the absence of a plausible alternative (once natural forcings have all but been ruled out as the dominant driver of the current warming trend), then anthropogenic forcings start to look very convincing indeed. I'd totally agree that predicting 'what happens next' is something that is so uncertain as to warrant great skepticism - especially when it comes to addressing possible mitigation steps - but in terms of 'what has already happened', the picture is alot clearer than many global warming deniers care to admit.

Aw comeon. Surely you know me better than that by now.

Sorry, that was a cheap shot.

it's a silly claim - that somehow man has now eclipsed nature in terms of our influence on the temperature.

It would also be a silly claim to say that man cannot have an influence on the temperature... I wouldn't say we have 'eclipsed' nature - but we have certainly altered the way in which natural systems are capable of responding to changing CO2 levels, for example. Collapse of ocean ecosystems (via ocean acidification for example) and deforestation, both of which we rely on to remove/fix carbon (and produce the oxygen we breathe!!) are just two ways in which man's activities can (and are) having a drastic effect on climate/atmospheric GHG content. As natural carbon sinks become saturated, so more CO2 stays in the atmosphere. Hence, it is not only the absolute quantity of GHG emissions that is important, but also the rate at which we have been pumping them out is highly significant - since the natural systems that normally adapt to fluctations in atmospheric CO2 concentration are simply not capable of responding in the same way as they always have done in the past...

 

[Danoff]

True - plenty of uncertainty remains, but in the absence of a plausible alternative (once natural forcings have all but been ruled out as the dominant driver of the current warming trend), then anthropogenic forcings start to look very convincing indeed.

It depends on how credible you think the science is that has ruled out natural forcing. Before I'm willing to go along with science, I need it to accurately predict something. I need some evidence that the model is good, that the science is sound, that the theory translates to practice. And so far, climatology has had very little of that sort of validation.

 

[Touring Mars]

Ironically, uncertainties in modelling the effects of natural forcings are just as uncertain as uncertaintites in modelling the effects of anthropogenic forcings! Why put your faith in one and not the other? What modelling of such natural forcings as solar activity and explosive volcanism have shown, as well as modelling of certain anthropogenic forcings too, is that none of them taken alone cannot explain the past/present warming trend... only when anthropogenic forcings such as GHG emissions are taken into account do we start to get anywhere near accurate models that fit the actual observed warming pattern.

 

[Danoff]

Ironically, uncertainties in modelling the effects of natural forcings are just as uncertain as uncertaintites in modelling the effects of anthropogenic forcings! Why put your faith in one and not the other?

When I say I don't believe their anthropogenic numbers, it implies that I don't believe their natural forcing numbers. Because for one to be wrong, the other needs to be wrong as well (assuming that the temperature measurement is accurate).

What modelling of such natural forcings as solar activity and explosive volcanism have shown, as well as modelling of certain anthropogenic forcings too, is that none of them taken alone cannot explain the past/present warming trend... only when anthropogenic forcings such as GHG emissions are taken into account do we start to get anywhere near accurate models that fit the actual observed warming pattern.

...assuming that the model for natural forcing is accurate. I'd like to see some evidence that these models are actually accurate - some predictions, some concrete testing. This is not a particularly straight forward discipline, it's not one humanity has been involved with for long, and it's not one that we have a particularly good track record with.

 

[Touring Mars]

When I say I don't believe their anthropogenic numbers, it implies that I don't believe their natural forcing numbers. Because for one to be wrong, the other needs to be wrong as well (assuming that the temperature measurement is accurate).
*snip*
I'd like to see some evidence that these models are actually accurate - some predictions, some concrete testing..

Who's they? The great global warming scientists conspiracy? The only studies/attempts to model solar variation, for example, are all done independently and pretty much universally agree that solar variation alone cannot explain the observed change in global temperatures in the 20th Century... Here is an example. The PNAS paper I cited earlier uses solar activity models by Wang et al. (Astrophysical Journal, v. 625, (2005)) and Bard et al. (Tellus Ser B, v. 52 (2000)) and both show solar radiative forcings are lower than radiative forcings assigned to human GHG emissions (as stated in Joos et al., PNAS, 105 (5), (2008)). Joos et al. also show that forcings attributed to volcanism actually predict a cooling effect over the same time period where we have actually observed warming.

 

[Danoff]

Who's they? The great global warming scientists conspiracy? The only studies/models/attempts to model solar variation, for example, are all done independently and pretty much universally agree that solar variation alone cannot explain the observed change in global temperatures in the 20th Century... Here is an example.

I was pretty much thinking of the IPCC. But I'll extend the same skepticism to any climatologist. I need proof that they're right.

The PNAS paper I cited earlier uses solar activity models by Wang et al. (Astrophysical Journal, v. 625, (2005)) and Bard et al. (Tellus Ser B, v. 52 (2000)) and both show solar radiative forcings are lower than radiative forcings assigned to human GHG emissions (as stated in Joos et al., PNAS, 105 (5), (2008)). Joos et al. also show that forcings attributed to volcanism actually predict a cooling effect over the same time period where we have actually observed warming.

Yea but where's the validation for these predictions and models?

 

[Touring Mars]

Perhaps we are talking at cross-purposes here a bit... Models do two different things - model the past and predict the future - and certainly one is alot harder to "validate" than the other. How do you validate a prediction other than to wait and see what happens? Like I said, predictions about global warming - consequences, severity etc. - may well be more uncertain (by definition, we are predicting things that haven't happened yet!) But most reliable scientific models thus far have shown that if you fail to take into consideration the effects of anthropogenic GHG emissions and their effect on climate, then you cannot accurately model the observed past climate data... and that is testable/quantifiable.

As for the IPCC, here is a diagram (which you've no doubt seen before) that illustrates that point from their website.

That said, some scientists, using the best climate models available at the time (and even acknowledging their limitations) did "predict" that anthropogenic climate change was not only possible but probable - a notable example being a certain Carl Sagan (Sagan et al., Science v. 206, No. 4425 (1979))...

 

[Danoff]

But most reliable scientific models thus far have shown that if you fail to take into consideration the effects of anthropogenic GHG emissions and their effect on climate, then you cannot accurately model the observed past climate data... and that is testable/quantifiable.

Reliable in the sense that they can "reconstruct" past data. In my line of work, we do a lot of after-the-fact fitting, and predicts. We call the stuff that happens in the future "predicts" and the stuff that happened in the past that we're fitting to "reconstruction".

Reconstruction is far easier than prediction, and a good reconstruction can still be wrong. It's a start, for sure, but I'd like to see a few predictions come true. So far, most of them have not come true. I don't think any of them predicted the flattening of temperature we've seen in the last few years.

 

[Famine]

PNAS

Wang et al.

My work here is done.

 

[Touring Mars]

I don't think any of them predicted the flattening of temperature we've seen in the last few years.

What "flattening" would that be?

(from Hansen et al., PNAS, v.103, no. 39 (2006))

My work here is done.

 

[Sureboss]

Of course you shouldn't also forget that we take out what takes in CO2 in the form of deforestation. I've read somewhere that the 'trees' (broad term here folks) are taking in more CO2 then Scientists think?

 

[Danoff]

What "flattening" would that be?

Here you go

 

[Touring Mars]

I did address that in a previous post and I maintain that this 'levelling off' is not quite what is appears to be. Notice that the same thing would happen if the graph ended in 2000, 1992 or 1985... notice that the black line in that graph is not (for all we know) the 5 year mean... plus, the general trend of the two graphs is the same, but the detail is slightly different. The Hansen paper I cite shows 2005 as being warmer than 1998 (an abnormally hot year due to a powerful El Nino event), but the CRU data is slightly different - the significance of the black line levelling off like that is not convincing evidence that 'global warming has stopped'...

Of course you shouldn't also forget that we take out what takes in CO2 in the form of deforestation. I've read somewhere that the 'trees' (broad term here folks) are taking in more CO2 then Scientists think?

Definitely - anthropogenic forcings include alot more than GHG emissions.

 

[Danoff]

I did address that in a previous post and I maintain that this 'levelling off' is not quite what is appears to be. Notice that the same thing would happen if the graph ended in 2000, 1992 or 1985... notice that the black line in that graph is not (for all we know) the 5 year mean... plus, the general trend of the two graphs is the same, but the detail is slightly different. The Hansen paper I cite shows 2005 as being warmer than 1998 (an abnormally hot year due to a powerful El Nino event), but the CRU data is slightly different - the significance of the black line levelling off like that is not convincing evidence that 'global warming has stopped'...

I definitely agree. But I'm certain that the prediction was that the last few years would be hotter. I know that the hurricane predictions have been horribly, horribly wrong.

 

[Touring Mars]

I'm certain that the prediction was that the last few years would be hotter.

Is the fact that the 5 hottest years since 1890 have all occurred since 1998 not a good enough validation of that prediction? Or is it because we haven't seen a steady year-on-year increase since 2000 (which would be the first time such a uniform change had ever been recorded) that is the problem? Or is it because the spike at 1998 creates the misleading impression that the following years were 'relatively cool'...? 1998 was exceptionally hot due to a well-established El Nino event, which explains why there is a spike there. Take 1998 away (or atleast bear in mind the reason why it is so high) and one's perception of the 1999-2007 period changes a bit... In any case, the data from Hansen et al. (the NASA GISS study) actually shows that 2005 was hotter than 1998 - the hottest year ever recorded in the Industrial Age...

I know that the hurricane predictions have been horribly, horribly wrong.

All that says is the science of hurricane prediction is still uncertain (let alone the link between hurricane frequency/intensity and climate) - it says precisely nothing about the validity of anthropogenic climate change.

 

[Famine]

Is the fact that the 5 hottest years since 1890 have all occurred since 1998 not a good enough validation of that prediction? Or is it because we haven't seen a steady year-on-year increase since 2000 (which would be the first time such a uniform change had ever been recorded) that is the problem? Or is it because the spike at 1998 creates the misleading impression that the following years were 'relatively cool'...? 1998 was exceptionally hot due to a well-established El Nino event, which explains why there is a spike there. Take 1998 away (or atleast bear in mind the reason why it is so high) and one's perception of the 1999-2007 period changes a bit... In any case, the data from Hansen et al. (the NASA GISS study) actually shows that 2005 was hotter than 1998 - the hottest year ever recorded in the Industrial Age...

It's worth a note at this time that it's only since 1880 that we've really been able to measure the global surface temperature - and with improving accuracy since then. Its no coincidence that Industrial Revolution has lead to scientific revolution. It's also worth noting that our ability to measure global surface temperature has only a 0.2 degree confidence - and the period of 125 years we're talking about has only a 1.0 degree variance between lowest and highest points.

We have no real clue what happened before then, beyond marginally less accurate data which seems to say that just before the 1880s we left a low-grade Ice Age. I'd naturally have to question the validity of taking such an obvious low point in global temperature as a starting point - but the underlying point here is that the planet is always changing its climate, so any analysis which takes any temperature as a "zero" is fundamentally inaccurate.


I'm also wondering what happened between 1940 and 1980 which rendered the global mean surface temperatures so low and unchanging, especially given that carbon dioxide emissions from sources attributed to mankind increased at almost exactly the same rate, year-on-year as it did since then. I know that in the UK we didn't really start cleaning up our act with regards to air pollution until about 1980 - it's a coincidence that we've had cleaner but warmer air since then, but it's still amusing.

 

[Danoff]

Is the fact that the 5 hottest years since 1890 have all occurred since 1998 not a good enough validation of that prediction?

Not really. What we're interested in here is the trend. And they got the trend wrong over the last few years.

Or is it because we haven't seen a steady year-on-year increase since 2000 (which would be the first time such a uniform change had ever been recorded) that is the problem?

A year-on-year increase isn't necessary. I understand the variability in these data points. I happen to think that the variability isn't properly measured when looking at even 100 or 1000 years. But I'm also not the one trying to draw conclusions from it. If they want to draw conclusions from the last 100 years of temperature measurements, I'd expect a little more accuracy in the recent results. Isn't the trend supposed to be taking off exponentially or somesuch? Aren't we supposed to be looking at a catastrophic departure into the abyss here?

Or is it because the spike at 1998 creates the misleading impression that the following years were 'relatively cool'...? 1998 was exceptionally hot due to a well-established El Nino event, which explains why there is a spike there. Take 1998 away (or atleast bear in mind the reason why it is so high) and one's perception of the 1999-2007 period changes a bit... In any case, the data from Hansen et al. (the NASA GISS study) actually shows that 2005 was hotter than 1998 - the hottest year ever recorded in the Industrial Age...

I'm not really talking about any particular data point.

All that says is the science of hurricane prediction is still uncertain (let alone the link between hurricane frequency/intensity and climate) - it says precisely nothing about the validity of anthropogenic climate change.

It says that understanding atmospheric conditions and the interaction between the various climate mechanisms is still quite difficult, even for the state-of-the-art.

 

[Sureboss]

It's worth a note at this time that it's only since 1880 that we've really been able to measure the global surface temperature - and with improving accuracy since then. Its no coincidence that Industrial Revolution has lead to scientific revolution. It's also worth noting that our ability to measure global surface temperature has only a 0.2 degree confidence - and the period of 125 years we're talking about has only a 1.0 degree variance between lowest and highest points.

We have no real clue what happened before then, beyond marginally less accurate data which seems to say that just before the 1880s we left a low-grade Ice Age. I'd naturally have to question the validity of taking such an obvious low point in global temperature as a starting point - but the underlying point here is that the planet is always changing its climate, so any analysis which takes any temperature as a "zero" is fundamentally inaccurate.


I'm also wondering what happened between 1940 and 1980 which rendered the global mean surface temperatures so low and unchanging, especially given that carbon dioxide emissions from sources attributed to mankind increased at almost exactly the same rate, year-on-year as it did since then. I know that in the UK we didn't really start cleaning up our act with regards to air pollution until about 1980 - it's a coincidence that we've had cleaner but warmer air since then, but it's still amusing.

Here's another question to throw into the fire then..

Could position of where x amount of CO2 is released affect problems? We all know for example that forests take in CO2. So could say a tonne of CO2 released in the Sahara do more damage than a tonne of CO2 released in the amazon? Hypothetically speaking.

 

[Touring Mars]

Not really. What we're interested in here is the trend. And they got the trend wrong over the last few years.

I don't think they have - the 'trend' in the CRU data is not a five year mean. The five year mean is clearly shown in the Hansen (NASA GISS) data, however, and has clearly been rising since ~1970...

Isn't the trend supposed to be taking off exponentially or somesuch?

No. Even the most alarmist predictions are nothing like 'exponential'.

Aren't we supposed to be looking at a catastrophic departure into the abyss here?

Again, I'd say you'd been listening to the catastrophists too much. Although global warming has the potential to cause major problems for our species, it doesn't mean that all consequences are bad by default. Indeed, the number of increased deaths from heatwaves is projected to be less than the number of lives saved by milder winters...

It's worth a note at this time that it's only since 1880 that we've really been able to measure the global surface temperature - and with improving accuracy since then. Its no coincidence that Industrial Revolution has lead to scientific revolution. It's also worth noting that our ability to measure global surface temperature has only a 0.2 degree confidence - and the period of 125 years we're talking about has only a 1.0 degree variance between lowest and highest points.

The degree of confidence in climate data is getting higher (and the margin of error is getting lower) all the time. The most recent data actually has an error of just +/- 0.05 degrees. I also think there is more significance in the data than you are pointing out - even with a 0.2 (+/- 0.1) degree of confidence, the data clearly shows a significant change, way clear of the margin of error. The warming observed in the 20th Century is unequivocal.

We have no real clue what happened before then, beyond marginally less accurate data which seems to say that just before the 1880s we left a low-grade Ice Age.

If by 'real' clue you mean that we cannot go back in time and measure the 'real' climate, then yes - I'd agree... but it's also a tad misleading. That's akin to saying that we have no real clue what dinosaurs looked like because we can only reconstruct them from fossil evidence. However true that may be, it categorically does not mean that we cannot get a very good idea of what they or the climate was like from the evidence that is available today.

There are multiple lines of evidence that give us a very real indication of past climate - there are many different types of 'proxies' of past climate, including some very tangible/real indicators of atmospheric gas composition (i.e. bubbles trapped in ancient icesheets). Of course, the error attributed to such data is inherently larger, but even so, not only is the margin of error still low enough to show that 20th Century warming is unusual with respect to the past 1000-2000 years, the degree of confidence in paleoclimate data is increasing all the time as more data/better models are developed. To pretend that climate proxy data will ever be as accurate as direct measurements would be wrong. But by the same token, to dismiss climate proxies as useless or meaningless is equally wrong.

This graph showing reconstructions of paleoclimate (brown) and instrumentally measured climate data (black line) used atleast 12 separate sources of proxy data to reconstruct past temperature... we can see clearly that the margin of error is indeed alot higher for the modelled data (about +/- 0.5 degrees across most regions). So although the paleoclimate record is indeed less accurate, I'd say it was very far from having no 'real' clue... This paleoclimate modelling must be considered in the context of climate forcings. What we know about natural forcings up to and including the 20th Century is that they alone cannot explain why the temperature is rising in the way it is now.

the underlying point here is that the planet is always changing its climate, so any analysis which takes any temperature as a "zero" is fundamentally inaccurate.

I don't dispute the fact that Earth's climate has and always will change in any number of different ways, over any number of different timescales. You may be right that comparing absolute temperatures is pointless - but that is not what we are doing here. The take-home message is that the current period of warming is unusual in the context of the past millennium and no naturally occuring phenomena (natural forcings) can fully explain it. The fact that factoring in anthropogenic forcings provides a much better explanation, however, is significant.

I'm also wondering what happened between 1940 and 1980 which rendered the global mean surface temperatures so low and unchanging, especially given that carbon dioxide emissions from sources attributed to mankind increased at almost exactly the same rate, year-on-year as it did since then.

I guess the answer to that is 'nothing happened'... although anthropogenic global warming is largely considered to have 'begun' at the start of the Industrial Revolution, the fact that anthropogenic forcings have become more dominant drivers of global climate than natural forcings is a relatively new phenomenon.

It's analogous to a point Danoff made some time ago about the suggestion that it took the US ten years to put a man on the moon - as he said, it didn't take 10 years - or a 100 years... it took the entire history of mankind to put a man on the moon. Similarly, when discussing the fact that anthropogenic radiative forcings are now a problem, it hasn't always been the case - even though it is now. What the climate record between 1940-1980 shows is that, despite increasing GHG emissions, natural forcings and anthropogenic forcings were balanced during that period (Note that it doesn't mean that anthropogenic forcings weren't around). Since then, however, anthropogenic forcings - such as massive deforestation and continuing global rises in GHG emissions have become more significant, and the warming in the late 20th Century (from ~1975 onward) is attributable in the main to anthropogenic forcings.

 

[Famine]

The degree of confidence in climate data is getting higher (and the margin of error is getting lower) all the time.

Exactly my point about global mean temperatures - the further back you go, the more inaccurate you get, until we (very quickly) reach a point where we can say roughly what the climate was like, but not what the temperature was to any degree of meaningful (well, when placed into the context of a 1.0 degree variance over 125 years) confidence...

I don't dispute the fact that Earth's climate has and always will change in any number of different ways, over any number of different timescales. You may be right that comparing absolute temperatures is pointless - but that is not what we are doing here. The take-home message is that the current period of warming is unusual in the context of the past millennium and no naturally occuring phenomena (natural forcings) can fully explain it. The fact that factoring in anthropogenic forcings provides a much better explanation, however, is significant.

But it's a highly dangerous position to take. We don't have a workable mechanism for how carbon dioxide causes global warming. We don't have a working knowledge of how much carbon dioxide causes how much heat absorption. We don't know how increasing carbon dioxide results in increasing global mean temperatures. The assumption is that it just does and that, since we can't explain what we're seeing from what we understand of natural sources (not much) then what mankind is doing must explain the rest. Even though we don't understand how what mankind is doing can explain the rest.

I guess the answer to that is 'nothing happened'... although anthropogenic global warming is largely considered to have 'begun' at the start of the Industrial Revolution, the fact that anthropogenic forcings have become more dominant drivers of global climate than natural forcings is a relatively new phenomenon.

It's analogous to a point Danoff made some time ago about the suggestion that it took the US ten years to put a man on the moon - as he said, it didn't take 10 years - or a 100 years... it took the entire history of mankind to put a man on the moon. Similarly, when discussing the fact that anthropogenic radiative forcings are now a problem, it hasn't always been the case - even though it is now. What the climate record between 1940-1980 shows is that, despite increasing GHG emissions, natural forcings and anthropogenic forcings were balanced during that period (Note that it doesn't mean that anthropogenic forcings weren't around). Since then, however, anthropogenic forcings - such as massive deforestation and continuing global rises in GHG emissions have become more significant, and the warming in the late 20th Century (from ~1975 onward) is attributable in the main to anthropogenic forcings.

Anthropogenic forcings, schmanthropogenic forcings.

Trees aren't that important in atmospheric carbon dioxide extraction for a start, even if we assume that carbon dioxide is an important, which is something we don't understand or can offer acceptable explanation for.

That notwithstanding, carbon dioxide emissions rose between 1940 and 1980 at almost the exact rate they have since and global mean temperature dipped. Meanwhile Amazon deforestation was at a higher rate, year-on-year, than at any point in history, save for 1995, 2002, 2003 and 2004. So that's unprecedented levels of anthropogenic forcings (GHG emissions, deforestation) but reduction in global mean temperatures...

Comically, 1980 saw a massive drop in global mean temperature, following an unprecedented (outside of historical and geological record) natural release of carbon dioxide into the atmosphere as Mount St. Helens went mental. The mountain still releases over 1,000 tons of carbon dioxide into the atmosphere every day - the equivalent of 6.4 MILLION vehicle kilometres for average cars. Every day.