Last wednesday two informed people from across the aisle (on this issue) had a conversation on climate change, co2, climate modeling and human activity. For reasons of anonimity, their names have been abbreviated.
Me: Hey guys, thanks for doing this. Please just identify yourselves shortly by either AC or IP (shorthands of your reddit usernames) and I’d ask AC to kick off by answering the main question: is there significant climate change, and is human activity to blame for it?
AC: I’d put it this way, there are significant climate signals, significant in the sense that they are both statistically significant, and are also significant given modeling uncertainties. The climate signal we see has a predominant human component, but there are other factors. Also, there are some domains where we don’t see a climate signal (truth in advertising).
IP: Man is responsible for shaping the environment. Since the Romans deforested Europe for wood. Dammed rivers, etc. So the question is not if Man has changed the environment, we have, we do. No question. The question is really about CO2. Will we all catastrophically die due to CO2 (as we are told). I think the answer is no. CO2 is the second most important compound to life on this planet.
CO2 levels have been much high in the past, life flourished. This biggest ‘explosion’ of life was in the Cambrian period when CO2 was >10,000ppm. Understanding earths geological history, oceans have been higher even just 6k years ago. CO2 level have been higher. In fact the earth is greening in response to higher CO2. Could argue there is a lack of CO2, the lowest in 5 billion years.
While the CO2 concern had/has some merit, potential for slight warming, the whole movement has been hijacked by special interest, big business, and a million other cause-du-jour “causes” attached to “climate change”. The movement has lost its bearings. It now political. We cannot even feed our homeless, we expect politicians to change the earth’s temperature with more taxes?
AC: Hmm….I don’t know if I agree that we’ve been told we will all catastrophically die due to CO2. I think the big issue with greenhouse gas emissions are changes, for example to the arctic. We have a window into high CO2 levels from the eocene when it was estimated to be about 1200 ppm. The arctic was forested. Right now, there is a huge loss of sea-ice in the arctic
IP: …changes, there will be winners and loosers with any climate shift, natural, or man made. We only hear everything bad.
AC: There is a loss of habitat for polar bears, and most researchers point to the current trends – probably the arctic fox as well. There is already a net shift in species due to climate change. There are scare stories for sure. And, I don’t agree with many of them.
IP: You mention polar bears. Polar bears are doing better than ever.
AC: Not from the sources I’ve both read and people who have studied the arctic. I know a researcher who has personally told me that the loss of sea ice is impacting polar bears.
IP: And that gets to my origianl point, the science has been highjacked by special interest. The science is boring, try reading the IPCC reports, no one does. But the scare stories turn a lot of people off, the failed predictions, etc.
AC: Now, I have not been to do a survey of polar bears, so I have to go on the word of this person I know, but he’s been reliable in other contexts. I have read the IPCC reports. I’ve also read the 4 year reports in the US, also the World Meteorological Organization’s report. And a fairly large number of journal articles.
IP: The ice is not effecting the polar bears. Their numbers have increased from the 70’s, numbers in the 5-10 thousand, they are over 25 thousand now. They were hunted, until a moratorium, since, numbers are doing great.
AC: I’d have to check my sources, IP. I think we disagree on this point, but I’d have to dig a bit to either verify or not, but again, I’m giving you my source.
Me: I think we got to the end of the polar bear issue.
IP: The IPCC reports (AR6). They mention uncertainties like 2500 times. If you add up all the uncertainties, the magnitude is way larger than the effect they are trying to account for. They even say, in text, they do not need to account for these uncertainties, to know man is causing change. They basically ignore it.
AC: Louise Archer’s January paper seems to be in accordance with my understanding of the polar bear situation and sea ice. Actually, they do account for the uncertainties. It’s crucial to understand the uncertainties, and they believe they’re well quantified enough to make the statement that we are seeing a human induced signal. I think that it’s good and proper to talk about the uncertainties. For example, how we measure the Earth’s albedo is a crucial uncertainty
IP: We cannot even account for Clouds, this is the largest uncertainty, including latent heat effects. Clouds dwarf any CO2 effect.
AC: https://www.science.org/doi/10.1126/science.adp3752
IP: I am avoiding links, we could do that all day.
AC: Fair enough. We can account for clouds, yes. There’s a question of how to parameterized the fine grained structure.
In the early days of weather modeling and climate modeling, the grid sizes were far too coarse to capture the fine grained structure of clouds, and that requires parameterizations. These have gotten quite good since about 1980 onward.
I can even support the concept of a kind of panic that’s conveyed to your point. There has been no significant uptick in landfalling hurricanes in the US. Also, no significant uptick in Cat 3-5 land falling hurricanes in the US. This, despite warming temperatures in the Atlantic basin. The WMO agrees with this – that there is no significant climate signal in hurricanes.
IP: But every hurricane is blamed on CC. Where we should really steer the conversation, is the policy decisions. Should we spend Trillions on CO2? When we cannot feed homeless. We are still dumping raw garbage into the amazon river. I have no issue spending money on.
AC: Yeah, this is something that highly irritates me. I hear on the radio that hurricane X is due to climate change, and I just shake my head. I’ve spoken with three hurricane experts and they don’t disagree with me. And…I have a conjecture as to why the number of hurricanes hasn’t increased.
IP: And I think that is partially getting to my point. Why we still see so many non believers. The cry wolf syndrome, turns a lot of people away.
AC: I don’t disagree on the cry wolf problem – the hurricane issue is a case-in-point. Warm water temps and low wind shear are needed for hurricane formation.
IP: For anyone who scratches just beneath the surface, we see it is not true. If that is not true, what else is not true.
AC: My conjecture for a lack of a climate signal is that while water temps are rising, there is also an overall increase in windshear, which inhibits formation. Again, you have to get into the data and modeling.
Take carbon dioxide levels.
Me: Nice to see such agreement on hurricanes. On the topic of temperature: has there been reported climate change due to human activity, has it already taken place in your opinion?
In the past 100 years or so?
AC: Yes – the signal of human temperature influence is probably from about 1980 onward.
I have a plot, but I don’t know if that’s something that’s allowed?
Me: Absolutely!
IP: The CO2 effect is already saturated. Adding more has very little effect from this point forward. The “window” is closed already.
AC: 
CO2 levels certainly aren’t saturating. What effect is saturating, in that case?
CO2 levels continue to rise.
That’s the Keeling curve the last time I checked in. It’s from Mauna Loa.
IP: That looks a scary graph. Man, since the 1850’s has done nothing but flourish. Life is better now than ever. But we are told it is worse. Rising CO2 levels should be an indication of good times.
AC: You can see an annual variation associated with….trees
IP: Why is life worse now, than before? We should be celebrating. Life in the 1850’s was harsh, starvation.
AC: There is the loss of arctic sea ice, which I suppose you could argue is a positive because of a northwest passage for vessels, but for me, it’s a loss of habitat for animals and species that have evolved for that environment. The arctic had been the hardest hit due to the albedo feedback effect. There is a fair amount of stress on the lobstering industry in Maine.
IP: But the artic has been ice free before. Before man. What caused that. Sea levels were 2m higher 6k years ago. During the last interglacial, like we are in now, ocean levels were 24m high than now, before SUV’s.
AC: I can’t disagree that a lot of progress had been made due to technological innovations, but the primary thesis that was asked was whether there is a human climate signal or signals, and I’m saying “yes”
As I said, during the Eocene epoch the arctic was ice free.
Me: Yes, to that: IP, could you elaborate on your point earlier about co2 saturation: “The CO2 effect is already saturated. Adding more has very little effect from this point forward. The “window” is closed already”?
IP: Greenland was Ice free too, before man.
AC: and it was because we had CO2 levels estimated to be above 1000 PPM.
Yes, the Eocene – and it also gives a window into what changes we might get for high CO2 levels. Paleoclimatology is fascinating because it gives us a window into how the earth responds to different forcing functions and we can apply that to out current era. And people for that matter. I’m surprised you didn’t invoke the Medieval Climate Anomaly (or Medieval Warm Period).
IP: [to your question:] CO2 only acts at certain wavelengths. You can see the change from 50 to 800ppm in this graph.
At zero PPM there is an open window. 400ppm to 800ppm, the effect is very tiny, an only at one wavelength. The bandwidth is already saturated at 400ppm.
AC: That’s an odd set of units on the horizontal axis. My understanding is that the emissivity is mostly in the infrared. 15 microns. Took awhile to get there. Where does that plot come from? It’s odd. It doesn’t look like one wavelength – it looks like a range of wavelengths for starters.
IP: I purposely did not come with “slides”. The CO2 effect is logarithmic. The more CO2 that is added, the less effect it has.
AC: But our emissions at the moment are exponentially increasing.
Me: If the graph is correct, would this change things in a big way AC?
AC: I’m not saying that I can immediately agree or disagree on whether it’s logarithmic, but even if it is, the product of an exponential growth in emissions with a logarithmic dependence could generate all sorts of possibilities.
[to your question:] Not really, Mr. Editor – I do have faith in the modeling and estimates of uncertainties. Knowing people doing this work, it if is indeed logarithmic, then I would strong believe that it’s in the models. But, the claim has me curious to track it down.
IP: You are welcome to review when we have more time. But yes the effect is logarithmic
AC: As I said, the result depends a lot on where we are on that curve and what the RCP’s are.
IP: I am trying to avoid turning this into a link to website conversation. The effect of CO2 is logarithmic.
AC: OK….even if I buy this, and you do have me curious, you will have to admit that even with a logarithmic behavior, there can still be a rise (not a saturation), particularly where you sit on that curve, and if the emissions are increasing exponentially, there is still a net increase in global temperature. Which kind of leads us to the modeling and also the current trends, particularly compared with the historical record.
IP: The only way the IPCC can make catastrophic climate change come true is will “feedbacks”. These are all based on models. The earths climate has been relatively stable for 5 billion years, CO2 at 10,000ppm to 180ppm. This would indicate the feed backs are not positive, but negative. There is no runaway Greenhouse effect. It would happened billions of years ago.
AC: I’m not claiming a runaway effect. And there are positive feedback effects, like albedo, which is why the arctic is particularly hard hit.
IP: Not suggesting you were, but a lot of others. I did not invent the term.
AC: And….actually I don’t agree that the climate has been relatively stable for 5 billion years – But, it depends somewhat on your definition of stability. The eocene is a fairly extreme period compared to the recent glacial epoch. And, I can definitely see that there are negative feedback effect, and hopefully properly accounted for as well.
Me: So what would you say you both agree on: a rising temp is occurring, the arctic hard hit, manmade effects are true. Disagree on modelling, co2’s effect?
AC: I really have to look into the CO2 question whether it’s logarithmic. I’d like to understand the mechanism. I suppose here is one possibility – there is the question of emissivity. As you get to a full coverage of CO2 and the emissivity in a simple model reaches 1, then all the heat in the important infrared band would get fully absorbed and then remitted isotropically and then there is no increase. But I believe we’re far from that point.
IP: Rising temps, temps have risen (and fallen) before. Artic has been ice free before, Greenland has been ice free before. We are comparing ONLY 100 years, in earths billions of years, and saying, look OMG. We couldn’t even record the artic extent fully until the 1970’s when the first satellites went into orbit.
AC: Climate proxies are challenging, to be sure, but they do extend much further back in time. Ice cores, for example. And, I don’t disagree that the arctic and Greenland have been ice free before. As I said, the Eocene is a great example.
And, you can get many climate proxies, say, in Greenland. Ice cores, sediment cores etc.
IP: Anyway the earth, even just in the last 10k years, a blink of an eye in geological timescales, we have had very pronounced, ups and downs in this interglacial.
AC: Yes, we’ve had pronounced ups and downs, I agree. Many forcing functions also at work.
IP: Here is a high resolution ice core from greenland. It was warmer back in 6-8kya. than now. Can even see as CO2 levels started increasing around 6kya, the temperature kept falling.
AC: The question is whether we are seeing a human induced set of climate signals presently. But that does not equate causally – the can be other effects going on like AMOC. It may be one effect, but there may be others.
IP: ….The real question, is what should we do about it, even if it was true. Do we send trillions off the the UN to fix the weather?
AC: For example, I’m scratching my head about the MWP.
IP: …the AMOC scare has been called off again.
AC: I am confining myself to the parameters set forth by the Editor – which is whether there’s a human induced climate signal. Yes, I’ve read the AMOC papers – I’m not trying to claim a scare on that or lack thereof. It’s just that it’s another source of potential variability.
IP: We are getting to an hour. Should we both summarize?
Me: Yes, you guys have been more than generous with your time.
AC: Oh, yeah, it’s getting late.
IP: I’ll go first. Life with more CO2 has never been better., trees love the stuff, the second most important compound to life. All the “scare” stories are not coming true. Earths history is riddled with variation, up, down…it never stays the same. Is colder better? But we know it never stay constant.
Me: That’s good as a closing statement IP, but let’s agree to disagree, what would you (broad strokes) agree on?
AC: The question the Editor set forth was whether we are seeing a human-induced climate signal or signals. I claim ‘yes’. I haven’t seen a refutation on that point. CO2 is definitely rising, global temperatures when averages are definitely rising when averaged over an appropriate period. The current warming has a strong human component. The arctic is the most strongly affected at the moment.
Questions of how we act whether it’s all good is another matter – happy to ponder that, but it’s a separate question.
Me: Ok, very nice. Would you agree with this IP? A gradual warming (non-runaway) with co2 as a decent factor.
IP: Where I think we agree, we as people can always do better for the environment. Everyone wants clean water, air and land. Where we may disagree, the Trillions being spent to slay CO2, could be much better spent on immediate, real problems, solvable today, for pennies on the dollar, that would have immediate effect (dumping garbage into the Amazon)
AC: But, the question posed – it sounds like you don’t disagree that the current warming has a strong human component. I agree that we’ve had substantial climate variability over time with forcing functions clearly other than humans.
Speaking of CO2, I have to leave in a tick to pick up my car at the mechanics.
Me: Thank you AC and IP! I appreciate it, very informative.
IP: Ok, thank you. While a little awkward through a chat window, it was fun, and an. Nice to meet everyone experience. Keep well all, we will over come.
AC: Nice to meet y’all. Be well, bye!