[evan_au]

the Vostok ice core  data that makes me skeptical

You should be skeptical of using a single data source for something which varies greatly in different locations at different altitudes at different times.
- We see that with CO₂ levels and temperature at different points on the globe
- We see that with the Greenland ice cores, where the initial core gave misleading results until they repeated ice coring in very different locations at different altitudes, and compared them
- A bit hard for Lake Vostok, since it is at a single elevation and a confined location; but I guess they could take additional ice cores at other ice lakes in Antarctica to come up with a consensus
- Unfortunately, there are no surviving frozen lakes in Hawaii...
- Other useful data over 1 million+ years comes from the remains of microscopic sea life on the sea floor

See: https://www.carbonbrief.org/factcheck-what-greenland-ice-cores-say-about-past-and-present-climate-change
 

[evan_au]

something very nonlinear is going on

This is true in general for chaotic systems.

It's especially a problem with climate and hydrodynamics, since the entropy of vortices spinning off other vortices gives a one-way arrow to time.

It is less of a problem with systems like motions of the planets, where kinetic + potential energy is conserved over time.
- The thing you can't account for is an "external" influence like a planet being ejected from the Solar system; the modeler doesn't know it was there, so their predictions beyond that point will be totally wrong.

At least for climate, we have a historical record stretching back over a million years, to which we can try and fit the known historical events.
- But it doesn't quite fit (yet), which is why modelers are trying to tackle potential external factors like the dust in the plane of the ecliptic.
- It has been suggested that we could seed algae in the oceans with essential minerals to soak up carbon dioxide
- Currently, Earth's orbit takes us through this dust on 2 days of the year.
- If Earth's orbit were taking up this dust 365 days of the year, that might provide an external input that feeds algae and soaks up CO2?

[alancalverd]

See: https://www.carbonbrief.org/factcheck-what-greenland-ice-cores-say-about-past-and-present-climate-change
 

You rarely disappoint me, Evan, but the last graph in that reference clearly substitutes prejudice for observation!

something very nonlinear is going on

This is true in general for chaotic systems.

Indeed, but the consistency of the asymmetric sawtooth is not characteristic of chaos alone. It looks much more like a relaxation oscillator than a white noise source. 

BC sensibly pointed out that
1 Ice is reflective
2 Methane trapped as hydrates would be a very potent greenhouse gas
3 water vapour
but then reverted to the True Faith of carbon dioxide.

Never mind. At least the conversation made me think. 

[alancalverd]

If I read him right, Euan Mearns is skeptical that humans are causing temperature rise today because they didn't 100,000 to 400,000 years ago. See blog (not peer-reviewed):
http://euanmearns.com/the-vostok-ice-core-temperature-co2-and-ch4/

I just got round to reading the paper. Didn't see the word "human" or "anthropogenic" anywhere, but a well-susbstantiated conclusion that

The only conclusion possible from Vostok is that variations in CO2 and CH4 are both caused by global temperature change and freeze thaw cycles at high latitudes. These natural geochemical cycles makes it inevitable that CO2 and CH4 will correlate with temperature. It is therefore totally invalid to use this relationship as evidence for CO2 forcing of climate, especially since during the onset of glaciations, there is no correlation at all.

So just to reiterate my concern: given that climate change is inevitable and beyond human control, what are we going to do to ensure that our descendants can enjoy a decent and peaceful standard of living?

[Bored chemist]

reverted

What do you mean by "reverted"?

[alancalverd]

I think the usage was idiomatic, unless I have misread the implications of your replies 50 and 54. I'd go along with the implication of 57 if you hadn't challenged the validity of my proposed experiments in previous exchanges.

[Bored chemist]

reverted

What do you mean by "reverted"?

[chiralSPO]

Alan, let's say that your interpretation of the ice core data is absolutely correct. What does your model predict would happen if the concentration of CO₂ were to suddenly (geologically speaking) increase more than 40% higher than it was at any other local maximum on the ice core data? (as it has)

Is it reasonable to assume that the mechanism responsible for the slow return to baseline after the smaller CO₂ spikes will be able to reverse the current level and trend? I don't think that previous returns to normal are necessarily good predictors of future behavior given how significantly we have deviated from the previous data.

Also, if I understand correctly, you accept that increased CO₂ in the atmosphere will lead to buildup of thermal energy, just not an increase in temperature? (how I interpreted your multiple references to heat capacity and latent heat of water). Ok, let's say the temp doesn't increase at all. Where does the energy go? What does that mean for the climate?

[evan_au]

Didn't see the word "human" or "anthropogenic" anywhere...

Exactly my point!
- As I read it, Euan Mearns doesn't believe in "human"-induced or "anthropogenic" climate change.
- He works through various non-human mechanisms that may have affected Earth's climate in previous 100,000-year cycles (human hunter-gatherers being too small in number to be a significant contributor).
- And he tries to imply that humans can't be affecting the climate today, even though we have around 7 billion humans and a significant agro-industrial complex that didn't exist 100,000 years ago.
- Pardon my ignorance of Latin, but I think that is called a "non-sequitur"?

the last graph in that reference clearly substitutes prejudice for observation

I'm sorry that you didn't like the last paragraph - I thought the article was quite sensible about the need for calibration of your results from multiple sources.
- The last part was where the historical trend (over thousands of years) is calibrated and joined onto projections of the next 50 years (if we keep going as we are, vs if we can curb CO₂ rapidly).
- Perhaps it would be better described as "adding extrapolation to observation".
- Passive observation does not lead to any action.
- Extrapolation of two scenarios does not passively wait for the future to become history (by which time it will be too late to do anything about it!), but encourages us to actively choose our path.

[alancalverd]

Rather a lot to get through, but just to pick up on the last point. I was referring to the last graph in the Hausfather article whee the observed data clearly showed a decrease in the most recent Greenland temperature but the model projections just continued the previous rate of increase.

I'll work through the detailed energetics at a later stage, but it is worth noting that the 7 millibar partial pressure of atmospheric carbon dioxide on Mars is about 18 times than on Earth (0.4 mb) , and the mean solar heat input per unit area about 0.43 of the Earth value (from a 1/r² calculation) so if CO2 is a dominant  greenhouse gas and the absorption bands are not saturated, you'd expect Mars to be as warm as Earth. I've attached a table of the supposed relative contributions of greenhouse gases in our atmosphere and even if you take the most "favorable" ratio that CO2: other gases is 9:88, that still suggests that the greenhouse effect on Mars will be about twice that on Earth, even ignoring the absence of clouds. But it clearly isn't, which  casts some doubt on the warming significance of CO2 in Earth's atmosphere.

And whatever hypothesis you prefer, I haven't seen one that seriously suggests a positive feedback mechanism driven by CO2. So the historic (and current, for 20,000 years) sharp rises in temperature must be due to something else, over which we have no obvious control. That's the problem for life on this planet, and praying to the carbon gods probably won't solve it.   

On the one hand, working from an invalid hypothesis isn't always a Bad Thing. All the early work on the propagation of radio waves  was modelled on compression of the aether, right up to the development of radar and television, and it would indeed be a Good Thing if society were less dependent on the burning of fossil fuels. But developing radar without developing fighter aircraft, or spending a huge effort on decarbonisation whilst ignoring  the inevitability of climate change and sea level rise, would be beyond stupid. 

[evan_au]

you'd expect Mars to be as warm as Earth

The black body temperature of Earth is about -23C (about 250K).
- The average surface temperature is around +15C, so a greenhouse warming of around 38C.

The black body temperature of Mars is about -63C (about 210K).
- The average surface temperature is around -60C, so a greenhouse warming of practically nothing.
- Not so surprising since the atmospheric pressure on Mars is about 1% of Earth - a very thin blanket, indeed!

So even if there were no Greenhouse effect, you would expect Mars to be considerably colder than Earth.

But Earth's water vapor, methane & ozone make a significant contribution to Earth's habitability.
- Nobody denies that. It is believed that Earth suffered an extended "snowball Earth" fate in the long-distant past
- But increasing CO₂ & fluorocarbons (also a potent and long-lived greenhouse gas, but now with reduced production) account for most of the changes seen in the past 70 years or so.
See: https://en.wikipedia.org/wiki/Snowball_Earth

I haven't seen (a hypothesis) that seriously suggests a positive feedback mechanism driven by CO2.

What about large areas of frozen land in arctic areas (eg Greenland & Canada). As the permafrost melts to a greater depth, microbes will become more active in the soil, producing CO₂ and methane from stored carbon...
- That will further increase CO₂, producing more melting.... (positive feedback)

What we want tis that the melting permafrost turns into a carbon sink, rather than a carbon source!

[alancalverd]

- Not so surprising since the atmospheric pressure on Mars is about 1% of Earth - a very thin blanket, indeed!

But it is almost entirely CO2 - 18 times as much as Earth. So if CO2 is a significant contributor to the greenhouse effect, it will be 18 times as significant on Mars. As you say, the greenhouse effect on Mars is negligible, and one eighteenth of negligible is, in my maths, buggerall or less. Which implies that CO2 is not a significant contributor to the greenhouse effect on Earth.

But increasing CO2 & fluorocarbons (also a potent and long-lived greenhouse gas, but now with reduced production) account for most of the changes seen in the past 70 years or so.

Here's my beef. Coincident with?  Certainly. Causative of? Not proven.

As you say, increasing temperature will generate CO2 from all sorts of sources. So CO2 follows temperature. But what triggers the initial temperature rise from the bottom of the curve?

[Bored chemist]

I haven't seen one that seriously suggests a positive feedback mechanism driven by CO2.

Heating the oceans will cause them to lose CO2. It's slow, but it will happen.

[Bored chemist]

Here's my beef. Coincident with?  Certainly. Causative of? Not proven.

And here's my beef:
You know there were three blankets on the bed.
You know you have added a fourth
You know it is warmer.

and you ask "But where is the proof of causation?".

Well the answer is obvious: we know what blankets do.

[Bored chemist]

But it is almost entirely CO2 - 18 times as much as Earth.

In the sense that 95 is 18 times bigger than 0.04?

What you actually need to compare is the number of molecules of CO2  that shade each square metre.
That's proportional to the mass of CO2 per square metre

And if I have done the arithmetic correctly (And I apologise for the fact that cut+ paste doesn't work well for spreadsheets- if anyone really wants, I will post an image) ...
      Mars     Earth   RMM   convert to m/m         Mars   Earth
mass atmos    2.50E+16   5.15E+18   Kg               
% CO2 v/v   95.32   0.04   44   4194.08   1.76   %m/m   96.43806789   0.060716454
%O2   0.174   20.94   32   5.568   670.08   %m/m   0.128029785   23.11641
%N2   2.6   78.1   28   72.8   2186.8   %m/m   1.673952653   75.44019429
%Ar   1.9   0.93   40   76   37.2   %m/m   1.747532989   1.283325054
%H2O   0.03   0.16   18   0.54   2.88   %m/m   0.012416682   0.099354198
%CO2 m/m   96.43806789   0.060716454                  
Mass CO2   2.41E+16   3.13E+15                  
radius (Km)   3,389.50   6,371                  
Surface area   144344155.6   509968249.5                  
Kg CO2/Km2   1.67E+08   6.13E+06                  
ratio   27.24073449                     

There's 27 times more molecules of CO2 shading each square metre of Mars.


But then we need to actually look at the thing that the denialists bang on about without understanding.
The world of saturation of a transition.

Essentially, it's simple.
Imagine shining a beam of red light through some green liquid- say food dye in water.
Once the pathlength is long enough, virtually all the light is absorbed and so using a longer path doesn't absorb any more.
Equivalently, you could add more dye to the water. Once you have added enough to absorb almost all the light then adding more won't make any (meaningful) difference.

(And, as an aside I will just mention here that putting more blankets on a bed is also non-linear- how many would it take before the person reached  100C?)

However, imagine that instead of using red light , I used a beam of white light- a bit like sunlight.
It's true that the red light corresponding to the peak of the absorption would all be absorbed in the tank  of green water, but the other colours would still get through.
And it's clear, if you think about it, that the broader the absorption of the light by the dye, the more light will be absorbed. And also- crucially- the more dye you would need to add in order to saturate those absorptions.
So broader spectra are less susceptible to saturation.

The absorptions of IR by CO2 (and there are lots of them) are all broadened by either increasing the temperature, or increasing the pressure.

And both the temperature and pressure are higher on Earth than on Mars.
So a given amount of CO2 on Earth does a better job of absorbing CO2

And that's all beside the point.
Earth is warm-
Part of that is because of radioactive rocks.
Part of it is simply what you would expect of a black body near the sun.- heat comes in: heat goes out.

Part of it is because we have an atmosphere that acts as an insulator.
Part of that in turn is due to the greenhouse effects of the various gases- notable CO2 an water vapour.

And, when you do some complicated maths you can work out how warm the planet should be.

And then you come to the tiny effect that we are talking about; warming.

We all know that, roughly speaking, the Earth is at about 15C (on average).


But the actual issue is not the temperature. We can explain that (as above etc.). Nobody cared what the actual balance of those factors is, because they were (on our timescales) constant.

The issue is the recent rapid change in temperature.

So the trillion dollar question is "what factors are changing, and which could explain the temperature changes we observe?"

And the only plausible one is the CO2 concentration.

[alancalverd]

What you actually need to compare is the number of molecules of CO2  that shade each square metre.

Which is proportional to the partial pressure of the gas: 7 mb on Mars (OK, 7 hPa if you prefer!) versus 0.4 hPa on Earth. You need to account for the lower g of Mars, which will bring your figure closer to mine. So we agree on that, at least.

More about saturation later - I'm off to explore a bit of England at 900 hPa while the sun shines.

[Bored chemist]

Which is proportional to the partial pressure of the gas:

And to the depth of the atmosphere which is different; which is why I did the slightly more complicated calculation, and got a better answer.

I'm off to explore a bit of England at 900 hPa while the sun shines.

Have fun.
Let us know when you are back on the planet.

More about saturation later

Never mind that:
You really need to address this

Here's my beef. Coincident with?  Certainly. Causative of? Not proven.

And here's my beef:
You know there were three blankets on the bed.
You know you have added a fourth
You know it is warmer.

and you ask "But where is the proof of causation?".

Well the answer is obvious: we know what blankets do.

[alancalverd]

Didn't fly - the weather forecast didn't quite pan out! But I realised of course with g_M about 0.37 x g_E, I've underestimated the molecular concentration of CO2 on Mars.

To address the saturation question, I'm now trying to find a solar input spectrum comparing  stratospheric input with ground level to the 15 micron range (for Earth, not Mars). So far all those I've been able to locate have stopped short at about 2 micron. Any help you can give will be most appreciated! The reason is that all the transmission spectra I can find seem to show 0% upward transmission at 15 micron, indicating that the CO2 longwave band is indeed saturated, so adding a bit more CO2 won't make any difference.

[alancalverd]

And another thing. Not only must a climate model explain the historic very rapid rise in temperature, the slow decrease thereafter, and the CO2 lag, but also why it has always stopped at pretty much the same maxima and minima.

If CO2 is the driver, and saturation isn't significant, there is no obvious maximum and no reason for the temperature to decrease. But it has done, several times.

If CO2 is the driver and saturation is significant, then the temperature is unlikely to exceed its present value by much because we are already close to the historic maximum set by saturation.

[Bored chemist]

But I realised of course with gM about 0.37 x gE, I've underestimated the molecular concentration of CO2 on Mars.

Good to know that you can realise things when we point them out.