Global warming discussion III

[CoolSceptic]

Ah. This following post reminds me exactly why I usually choose not to engage in this ridiculous thread.

So Pixel42 seems to create a bizarre straw man, generates data that actually agrees with my original claim and then demonstrates astonishing incompetence with statistics.

First and most important point: the straw man. I did not claim 15 year trends were less noisy than 30 year trends. Your analysis isn't very good (too few points, and a strange decision to take the ratio of additive noise samples) but a decent analysis of sample near surface temperature data sets does indeed show that sample 15 year trends have greater variance than sample 30 year trends. I don't dispute this and this was never a part of my original claim.

I was addressing specifically the claim from lomiller and capeldodger that climate sceptics cherry picking 1998 had a big influence on the trend. I showed, with an example data set, that actually it is negligible influence, and most certainly does not result in a trend above the long term. Which leads to my second point - that your data corroborates my claim:

1996-2010: +.12 C per decade
1997-2011: +.05 C per decade
1998-2012: +.04 C per decade
1999-2013: +.07 C per decade
2000-2014: +.07 C per decade

Note that in the samples you have chosen, there are three that include 1998 and two that do not. The two that do not have trends of 0.07 C per decade. Even conceding to capeldodger (see above post) that the long term trend is 0.16 C per decade, your figures of +0.07 C per decade confirm that 1998 is not a particularly important driver of sample 15 year trends, nor does its exclusion cause trends to rise above the long term trend. In fact, the highest 15 year trend you calculate *includes* 1998 near the start of the series.

We then come to my third point, a very odd aspect of your analysis:

The largest trend is three times the smallest

This made me laugh a lot. Who on earth takes additive noise such as that on trends then declares a *ratio*??? Answer: someone who does not know what they are doing!

In your rather limited spread of data points, your results span 0.08 C per decade. But imagine if they had been 0 C/decade to 0.08 C/decade instead. You could claim the largest trend was *infinitely* larger than the smallest one! Oh dear. If it had been -0.04 C/decade to +0.04 C/decade, you would have had a trend -1 times larger! As you can see, using a ratio here makes no sense whatsoever. You have additive noise and the correct thing to do is to determine the spread. If you want to compare the spread with the ratio, you should use the sample standard deviation of the trends - but of course just using 5 points is not a good way to do this. Here is some MATLAB code to read and calculate all of the 15-year and 30-year trends in HadCRUT4:

hadcrutext = urlread('http://www.metoffice.gov.uk/hadobs/hadcrut4/data/current/time_series/HadCRUT.4.3.0.0.annual_ns_avg.txt');
data_table = textscan(hadcrutext, '%f%f%f%f%f%f%f%f%f%f%f%f');

num30yr_trends = size(data_table{1},1)-30;
num15yr_trends = size(data_table{1},1)-15;

ThirtyYearTrends = zeros(num30yr_trends, 1);
FifteenYearTrends = zeros(num15yr_trends, 1);

% Compute and store 30 year trend data
for loop=1:num30yr_trends,
    olsfit = polyfit(data_table{1}(loop:(loop+29)), data_table{2}(loop:(loop+29)), 1);
    ThirtyYearTrends(loop) = olsfit(1);
end

% Compute and store 15 year trend data
for loop=1:num15yr_trends,
    olsfit = polyfit(data_table{1}(loop:(loop+14)), data_table{2}(loop:(loop+14)), 1);
    FifteenYearTrends(loop) = olsfit(1);
end

% Display results
fprintf('Standard Deviation of 15 year trends: %.6f\n', std(FifteenYearTrends));
fprintf('Standard Deviation of 30 year trends: %.6f\n', std(ThirtyYearTrends));

On running it gives this result:

Standard Deviation of 15 year trends: 0.011321
Standard Deviation of 30 year trends: 0.007653

As expected, the 30 year trends which have twice as many samples show a reduction of standard deviation of a ratio of the square root of two. This is a valid ratio to determine - unlike the strange arithmetic you were doing above.

So in summary:-

- We agree 15 year trends in the temperature data sets show a higher standard deviation than 30 year trends, my analysis shows the spread is higher by a factor of approximately root 2;
- Your data corroborates my claim that exclusion of 1998 in the 15 year trends does not have a big impact, nor does its exclusion result in the trend jumping above the long- or short-term projections;
- I hope we can agree taking the ratio of largest to smallest trend has no useful mathematical meaning for trends with additive noise, and my more thorough analysis above shows the actual difference in noise between 15 year and 30 year trends of temperature data sets.

 

[CoolSceptic]

You've already explained it, so it's not really apt anymore.

But for curiosity sake, the impetus was due to me having set trend rates for medical insurance. There's a lot of noise, because there's not solely one cause for the observed trend - it's not just "inflation" in any normal sense of the word. There's unit cost inflation - how much doctors want their prices to go up for the same service year over year. But there's also changes in utilization due to advertising/new info/changes in medical practice etc., changes in the severity mix, changes in the induced utilization due to benefit changes, and changes in the mix or degree of negotiated reimbursement rates.

There's an underlying trend that can be seen... but only on a long enough time scale. We end up using 5 to 10 years of data to walk in to our underlying trend, and we have to control for all those other factors. If we tried to set trend based on just one year's worth of data, we'd be wildly inaccurate and basically just throwing a dart.

I was assuming that the "trends" in discussion here were a similar thing - a statistical trend rate. Based on that, trying to determine trend based on a couple of decades would be like me trying to set medical trend based on a week's worth of information.

But it seems to be the case that your "trend" and my "trend" aren't the same animal.

Emily's cat:

The points you raise are important, and understanding the behaviour of the climate system across scales is essential to interpreting what recent changes mean.

If you are interested, there is a useful way to characterise this behaviour of climate using autocorrelation functions or power spectral densities. There are some relatively simple relationships that emerge from this.

Unfortunately I have wasted what little time I have available today answering other (less interesting) points. If you are interested in discussing this further I might try and write something up, but it would take me a day or two (I am in a lab for the rest of the day which is sealed from the outside world and cannot easily access the internet). It sounds like you have some knowledge of statistics and time series analysis - are you familiar with spectral methods? I only ask because conventionally mathematicians and statisticians prefer to work in terms of autocorrelation functions, whereas my signal processing background means I am more comfortable explaining using spectral methods (they map to the same thing, just different ways of thinking about the same problem)

The only difficulty is that any discussion here tends to be disrupted. As you can probably already see, I have unpopular opinions here and my presence tends to result in a stream of straw man and nonsensical criticisms.

 

[Emily's Cat]

Very very difficult and has it's own set of consequences as it also is anthro.

Tangled in this is not only carbon but sustainable as well. Start with the lower hanging fruit and move out of coal which has not only carbon implications but many other negative consequences for the environment.

Inevitably society will be carbon neutral is we burn it all. Not a pretty outcome.

Emily - read through this to understand the long term consequences of carbon.

http://www.nature.com/climate/2008/0812/full/climate.2008.122.html

There is really no way back that has any practical possibility.

The climate IS altered.....it's how fast the consequences unfold that we are dealing with...IF we can get to a renewed radiative balance around 2 degrees C - then we have a new climate regime that is relatively stable...not a lot different than the Holocene optimum .some 8,000 years ago when civilization blossomed, - our biome can generally handle that.

Moving into the unknown territory of 3+ C - a global temp not seen in millions of years.....that's the risk that the world is trying to avoid.

That makes more sense.

BTW- Thank you very much for the information above. It was fantastic!

 

[bit_pattern]

Here's some more on why the so-called "pause" in the surface temperature trend is essentially a meaningless construct, beyond trying to figure out what the relationship between surface temps and an ever increasing energy budget actually is. Heat content continues to build unabated:

http://theconversation.com/ocean-depths-heating-steadily-despite-global-warming-pause-37047

The oceans are continuing to warm steadily despite an apparent slowdown in global warming at the earth’s surface, according to data collected by thousands of floating robots published today in Nature Climate Change.

Between 2006 and 2013, ocean waters shallower than 500 metres warmed by 0.005C per year, while between 500 and 2,000 metres the ocean warmed by 0.002C per year. While seemingly tiny, John Church, a sea level researcher at CSIRO and one of the study’s authors, said these numbers “represent a huge amount of heat”.

“It’s well over 90% of the total warming of the climate system. Although the whole climate system is warming, over this period and over earlier periods the majority of that heat is being stored in the ocean.”

 

[Elf Grinder 3000]

Question - I would really like this explained to me

1. Look at the temperature variation over the past 100,000 years

2. Look at the concentration of CO2 in the atmosphere

3. Notice that the CO2 concentration is relatively stable pre industrial revolution

Why not conclude that CO2 is not the major driving factor in climate change?

Thanks!

 

[Emily's Cat]

Here's some more on why the so-called "pause" in the surface temperature trend is essentially a meaningless construct, beyond trying to figure out what the relationship between surface temps and an ever increasing energy budget actually is. Heat content continues to build unabated:

http://theconversation.com/ocean-depths-heating-steadily-despite-global-warming-pause-37047

Absolute dummy question here: How does this work? How does the heat end up in the deeper water? I understand that water is a great insulator... I'm just not conversant on how that transaction happens globally. Is it just convection?

Like I said - it's undoubtedly a dumb question and I'm just thinking sideways.

 

[Emily's Cat]

Question - I would really like this explained to me

1. Look at the temperature variation over the past 100,000 years

2. Look at the concentration of CO2 in the atmosphere

3. Notice that the CO2 concentration is relatively stable pre industrial revolution

Why not conclude that CO2 is not the major driving factor in climate change?

Thanks!

What are the axes? Is the x-axis years?

 

[bit_pattern]

Why not conclude that CO2 is not the major driving factor in climate change?

Because physics.

 

[bit_pattern]

Absolute dummy question here: How does this work? How does the heat end up in the deeper water? I understand that water is a great insulator... I'm just not conversant on how that transaction happens globally. Is it just convection?

Like I said - it's undoubtedly a dumb question and I'm just thinking sideways.

Wind and ocean currents - the mechanics aren't perfectly understood, but from what I can glean they are the culprits.

https://theconversation.com/global-warming-stalled-by-strong-winds-driving-heat-into-oceans-22954

Previous research has already shown that cooler temperatures over the eastern Pacific are linked to a slowdown in worldwide warming, but researchers wanted to know why.

Data from ships and weather buoys revealed an unusual strengthening of the Pacific trade winds, which blow east-to-west near the Equator. In turn, that speeds up the “overturning circulation” of Pacific waters, driving warmer water down to depths of up to 300 metres in the western Pacific, while cooler water wells up in the ocean’s east.

When plugged into climate models, the effect of the strengthened winds is equivalent to 0.1-0.2C of surface cooling – which accounts for almost all of the observed slowdown in global surface temperatures.

Previous climate models missed this effect because the strong winds had never been observed before, Professor England said.

 

[CapelDodger]

What I was criticising is your decision to difference two months some way apart, then make a declaration on that basis.

Two months just under 15 years apart, 15 years being a period you apparently regard as significant.

I picked GISTEMP land and ocean (why not shake up the series a bit). Using their data, Jan 2000 to Jan 2014 differenced gives +0.46 deg C - about the same as NOAA (unsurprisingly, since their source data are similar). Data are here.

But then we look at Feb 2000 to Feb 2014 - just one month on - and the difference is -0.13 deg C. If we are to believe this as a useful metric, one month the pause has gone, the following month the pause is back and we actually have cooling.

What does that tell you about the slowdown? One month it's there, next month it's gone, then it's back again. It's far from robust, I'm sure you'll agree.

And I can choose months that give even more absurd results. I would pick Feb 1998 as a start point, but I don't want the peanut gallery to spit all of their coffee out, so I'll choose Feb 1995 instead. Feb 1995 to Feb 2014 gives me a delta of -0.32 degrees. What does this tell me about global warming? Short answer: just like your delta, absolutely nothing of any use at all. So why are you claiming that this delta shows the pause didn't happen?

Why are you claiming a pause did happen? It came, it went, it's gone now but when the January 2015 figures come in who knows? It's nonsense, frankly.

Since you may have forgotten, I responded to a specific claim you made:


So, I apologise for selecting the long-term trend in response to your claim about the long-term trend

Now we've clarified that by "long-term trend" you didn't actually mean "long-term trend" ...

I, of course, was referring to the actual long-term trend; you're referring to a projected long-term trend. These two things are not the same. The one refers to what has happened, the other to what hasn't yet.

I will concede the use of 0.16 deg C per decade. Note: it doesn't change my conclusions one bit. 0.066 deg C per decade is still smaller than 0.16 deg C per decade. So the trend in that period - rather than the delta (which can't tell us anything, as explained above) is most certainly below the long term trend AND the short-term projection of the IPCC.

I'm having some difficulty in finding any short-term projections in IPCC reports, which is hardly surprising since they wouldn't be at all robust. If you could point me to where you find them I'd appreciate it. The 0.16C (which is not universally accepted, by the way; many climate scientists think it gives too much weight to the recent slowdown and are sticking with 0.17-18) would refer to 30 years minimum. If the next 15 years warm at above that rate it could easily cancel out the slowdown, since the PDO is very likely to shift to its warm phase in that time and AGW will continue. That would be a surge if the last fifteen years were a slowdown, would it not?

 

[bit_pattern]

What are the axes? Is the x-axis years?

From what I can tell it's proxy temperature data from the most recent glacial/interglacial switch.

Elf Grinder asks us to look at temperature variation over the previous 100,000 years and look at CO2 levels... OK:

I'd say this is a very clear illustrative example of why not to conclude that CO2 is not the major driving factor in climate change!

It's not a reason in and of itself to conclude that it IS the major driving factor, but it certainly is one very strong piece in the myriad of evidence that does lead researchers to make such a conclusion.

 

[Emily's Cat]

From what I can tell it's proxy temperature data from the most recent glacial/interglacial switch.

I guess I'm just a bit surprised that the high bit goes back so long - looks like something around 7000 years? I figure I'm reading it wrong, or it's not a graph of what I think it's a graph of...

Without titles and links and stuff, I can't even figure out what in my assumptions is off.

I'd say this is a very clear illustrative example of why not to conclude that CO2 is not the major driving factor in climate change!

It's not a reason in and of itself to conclude that it IS the major driving factor, but it certainly is one very strong piece in the myriad of evidence that does lead researchers to make such a conclusion.

It's hard to tell with such a squished graph. It's like trying to look at stuff in the tail of a claims distribution - it's almost impossible to get it on a scale that makes it make sense while simultaneoulsy comparing it to the left end of the distribution for relativity.

It looks like the CO2 "leads" the temperature changes - not in terms of time scale, necessarily, but in terms of variability. I'm having a hard time putting this in to words. It looks like in past periods, the CO2 "pulls" the temperature. So when the CO2 spikes above, it "drags" the temperature behind it... and then when it falls below it "drags" the temperature down. I can envision it as a two balls attached by springs. The CO2 ball oscillates in a wave pattern around a central axis. The temperature ball is attached to both the CO2 ball and the axis, so it get's "dragged" by the motion of the CO2 ball... but not as far as it would if it weren't attached to the central axis. That's what I mean by the CO2 "leading" the temperature.

But in that right hand bit (the most recent time) the CO2 doesn't oscillate - it stays high. So the temperature line get's pulled further up. Going back to the springs model, the temperature ball would overcompensate for the interrupted oscillation.

How's that for a screwy way to look at it?

 

[CapelDodger]

Absolute dummy question here: How does this work? How does the heat end up in the deeper water? I understand that water is a great insulator... I'm just not conversant on how that transaction happens globally. Is it just convection?

A lot of it is convection, which may seem odd since we''re used to warm fluids rising and vice versa. What's actually happening is that denser fluids sink while lighter fluids rise, and seawater density depends on temperature and salinity. Warm salty water can be denser than cooler but less salty water so it sinks -taking its heat with it.

Warm water tends to evaporate and become more salty then down it goes. Horribly simplified I know but it gets past the instinctive "How can warm water sink?" we all first have.

There are a few places where this happens, such as the North Atlantic at the end of the Gulf Stream/North Atlantic Drift. Warm water from the south flows up there getting saltier and cooler until eventually it sinks under less salty water and either joins very deep currents flowing south again or mixes into the ocean higher up.

The details of ocean behaviour are still sketchy since the whole subject has been woefully neglected until recently. We know more about the surface of Mars than we do about the biggest thing on our planet apart from the planet itself - our oceans. The silver lining of "more research is needed" policies is that more research is actually being done, and not just where nuclear subs lurk.

 

[Emily's Cat]

Thanks CapelDodger! That helps some.

 

[macdoc]

Emily
Elf Grinder and many others do not understand the difference between forcing and feedback.

CO2 as a Feedback and Forcing in the Climate System

A fundamental misconception about the role that carbon dioxide plays in glacial transitions has helped fuel the argument that the lag time between temperature and CO2 in the paleoclimate record casts doubt on carbon dioxide as an important greenhouse gas.
It’s crucial that media reporting on climate change understand an important distinction between the dual roles of greenhouse gases as both forcings and feedbacks.
In the geologic past, carbon dioxide and other greenhouse gases acted primarily as feedbacks to external climate forcings. Our current and basically unprecedented experience is that we as humans are directly emitting carbon dioxide and other greenhouse gases that affect climate change.
That distinction – greenhouse gases as both forcings and feedbacks – is critical in understanding the behavior of these gases in the paleoclimatic and present periods.


same graph as above.
The figure to the right shows changes in temperature and CO2 concentrations over the past 450,000 years. Four distinct ice ages occurred during that time. The strong correlation of the curves makes it immediately apparent that some relationship seems to exist between temperature and CO2.
During both the transition in to and out of a glacial period, CO2 concentrations appear to lag temperature changes by an average of between 600 and 1,000 years (though some recent research suggests that this lag may be shorter than previously thought).
If CO2 lags behind temperature changes, it stands to reason that some other mechanism is responsible for the initial temperature change. In fact, we do know just such a mechanism that does a reasonably good job accounting for the initial cause and end of ice ages: changes in orbital forcing known as Milankovitch cycles.
Milankovitch cycles refer to the effects of periodic variations in Earth’s orbit on the amount of solar radiation reaching parts of the Earth’s surface. Three cycles are particularly important: the eccentricity of the Earth’s orbit (e.g., how elliptical the Earth’s orbit is); the axial tilt of the Earth (known as obliquity); and the change in the direction of the Earth’s axis of rotation (known as precession). Each of these Milankovitch cycles has a recurring periodic variation, and the overlap of these periods combine to change the total solar forcing in a way that helps explain Earth’s periodic ice ages, as shown below.

concluding

Current climatic changes are substantially different from those that occurred in the past. For one thing, they are happening at a much faster rate than changes in past glacial periods. Significant climate changes are occurring over the course of decades and centuries, rather than millennia. Scientists know that Milankovitch forcings are not having a significant impact on changes observed over the past century, as they do not operate on such a short timescale, and scientists have good measurements of what their effect should be.

For the first time, greenhouse gasses are primarily acting as forcings in the climate system instead of as a feedback to external forcing (though their role as feedbacks is still important, as illustrated in discussions of a potential methane feedback from melting arctic permafrost).
While the lag between temperature and greenhouse gas changes in the paleoclimate record is important in understanding the function of greenhouse gasses in the Earth’s climate, and has helped in estimating the effects of CO2 concentrations on radiative forcing, it in no way discredits the conventional knowledge that CO2 is forcing recent changes in the Earth’s climate.

http://www.yaleclimateconnections.o...a-feedback-and-forcing-in-the-climate-system/

This is SUCH a fundamental point you would think anyone pretending to be knowledgeable about climate would know the difference between a feedback and a forcing.....rather than face planting in a science forum

 

[CapelDodger]

I'd say this is a very clear illustrative example of why not to conclude that CO2 is not the major driving factor in climate change!

It's not a reason in and of itself to conclude that it IS the major driving factor, but it certainly is one very strong piece in the myriad of evidence that does lead researchers to make such a conclusion.

I think it's worth mentioning that the CO₂ data wasn't available when the conclusion was reached that the CO₂ feedback was the last piece in the Ice Age puzzle. It's confirmatory evidence, which is my favourite kind .

The first light-bulb was Milankovich cycles but the numbers didn't add up. The next light-bulb was Milanbkovich cycles plus albedo feedback but again not enough. The final light-bulb was CO₂ feedback and at last the numbers added up, at least roughly. You gotta love science.

 

[macdoc]

It looks like in past periods, the CO2 "pulls" the temperature. So when the CO2 spikes above, it "drags" the temperature behind it... and then when it falls below it "drags" the temperature down

You are not far off on the analogy...CO2 is earth's thermostat. Leaving aside human use of fossil fuels.
As oceans cool due to a shift in the orbital ( Milankovich ), the ocean absorbs more CO2 from the atmosphere magnifying the cooling effect.

As the oceans warm again due to the same shift.....CO2 is released into the atmosphere accelerating the warming.

Both of these are feedbacks.

Currently those.....we have overlaid that natural carbon cycle by boosting the C02 in the atmosphere from 280 ppm to over 400.
As a result, the fossil CO2 release now becomes a primary forcing - especially for the oceans. It overwhelms all other forcings including orbital and solar ( a magnitude lower ).

It is only dumb luck that we were drifting very slowly towards a cooling in the Milankovich cycle so that forcing is countering the fossil carbon a little bit instead of making it worse.
But it is very minor.

We're it....we dun it and it ain't going away.

 

[CapelDodger]

I was addressing specifically the claim from lomiller and capeldodger that climate sceptics cherry picking 1998 had a big influence on the trend.

For the record, I made no such claim. I pointed out to lomiller that 15 years ago is Jan 2000, which doesn't include 1998 and doesn't even suffer from autocorrelation with it (as 1999 does). 1998 has dropped off the short-term perch, so to speak.

 

[bit_pattern]

It looks like the CO2 "leads" the temperature changes - not in terms of time scale, necessarily, but in terms of variability. I'm having a hard time putting this in to words. It looks like in past periods, the CO2 "pulls" the temperature. So when the CO2 spikes above, it "drags" the temperature behind it... and then when it falls below it "drags" the temperature down. I can envision it as a two balls attached by springs. The CO2 ball oscillates in a wave pattern around a central axis. The temperature ball is attached to both the CO2 ball and the axis, so it get's "dragged" by the motion of the CO2 ball... but not as far as it would if it weren't attached to the cent

MacDoc has already answered, but in my words - there's an 800 year lag. A slight warming is forced by orbital changes in the Milankovitch cycle, which leads to oceans releasing CO2. As CO2 accumulates, the warming is enhanced. It's a feedback mechanism. And because the changes in solar radiation caused by the orbital variation are too weak to force the temperature changes observed in the records it is this lead/lag issue that helps instruct current projections on climate sensitivity and how the climate responds to shifts in atmospheric CO2.

Here's a good explainer:

http://www.skepticalscience.com/Why-does-CO2-lag-temperature.html

Or if you prefer videos, I quite enjoy this series from potholer54 - it's aimed at skewering denier talking points so can come across a tad condescending, but he's quite entertaining:

 

[bit_pattern]

I think it's worth mentioning that the CO₂ data wasn't available when the conclusion was reached that the CO₂ feedback was the last piece in the Ice Age puzzle. It's confirmatory evidence, which is my favourite kind .

The first light-bulb was Milankovich cycles but the numbers didn't add up. The next light-bulb was Milanbkovich cycles plus albedo feedback but again not enough. The final light-bulb was CO₂ feedback and at last the numbers added up, at least roughly. You gotta love science.

Indeed. It's a wonderful story. AIP do a really great timeline, for anyone interested:

http://www.aip.org/history/climate/co2.htm