ANSWER 1

Written response:

Thanks for the question Leland! There’s a lot of sub-questions in there, and I’ve tried to respond to each of them, so there is a ‘Too Long; Didn’t Read’ summary at the top and detailed responses below 😊.

Too Long; Didn’t Read’ summary

• Even though CO₂ and methane make up a tiny fraction of the atmosphere, they matter because they interact strongly with heat (infrared radiation) in ways that nitrogen and oxygen do not.
• The greenhouse effect operates day and night, and rapid desert cooling actually supports greenhouse physics rather than contradicting it.
• Water vapour is not ignored; it is the most powerful greenhouse gas, but it acts mainly as a feedback, not an independent driver.
• Past warm periods (Minoan, Roman, Medieval) were real, but they were driven by natural factors and were not globally synchronous.
• The original Hockey Stick graph was broadly correct: subsequent independent analyses, including those led by former sceptics, confirmed its central conclusion.
• Climate science today rests on multiple, independent datasets and physical measurements, not any single graph or scientist.   

The long version:

1. How can gases that make up only \~0.042% (CO₂) and \~0.002% (methane) of the atmosphere affect the temperature of the rest?
This question is understandable, because it seems counter‑intuitive at first glance. The key point is that climate influence is not determined by how much of a gas there is, but by what energy it interacts with. Nitrogen (78%) and oxygen (21%) dominate the atmosphere by volume, but they are almost transparent to infrared radiation, which is the form of energy the Earth emits as it cools. By contrast, gases like CO₂ and methane absorb and emit infrared radiation very efficiently in key wavelength bands. Even trace amounts of these gases can therefore restrict how quickly heat escapes to space. These gases act like an extra blanket. They stop heat from escaping easily, so the heat only gets out from higher, colder air. Cold air releases less heat, so more heat stays in the Earth system, and the planet warms up until things balance again. This is not speculation: it is measured laboratory physics, and the same radiative properties are used to model the atmospheres of other planets.

Key references

• Pierrehumbert, R. T. (2010). Principles of Planetary Climate. Cambridge: Cambridge University Press. https://www.cambridge.org/highereducation/books/principles-of-planetary-climate/5B5EEF0534CB6F69FB2E395DD21D3476#overview
• Myhre et al. (1998), New estimates of radiative forcing due to well mixed greenhouse gases, Geophysical Research Letters https://agupubs.onlinelibrary.wiley.com/doi/10.1029/98GL01908

2. Doesn’t greenhouse warming only operate part of the time because of night, clouds, and aerosols?
This is a common misunderstanding. The greenhouse effect does not depend on sunlight. It acts on outgoing infrared radiation, which the Earth emits continuously, day and night. In fact, greenhouse gases are especially important at night because they slow cooling. Clouds and aerosols complicate the picture but do not negate greenhouse warming:

• Many aerosols have a cooling effect by reflecting sunlight.
• Greenhouse gases have a warming effect by reducing infrared heat loss.

When all effects are added together, measurements show a net positive radiative forcing over the industrial era, dominated by greenhouse gases.

Key references

• Stephens, G., Li, J., Wild, M. et al. An update on Earth’s energy balance in light of the latest global observations. Nature Geosci 5, 691–696 (2012). https://doi.org/10.1038/ngeo1580
• Feng, J., Paynter, D., Menzel, R. et al. A strong constraint on radiative forcing of well-mixed greenhouse gases. Nature 652, 105–111 (2026). https://doi.org/10.1038/s41586-026-10289-x

3. Desert temperatures drop rapidly overnight -doesn’t this show greenhouse gases can’t retain heat?
Rapid desert cooling is real, but it actually supports greenhouse physics, rather than contradicting it. Deserts cool quickly at night because they have:

• Very low water vapour
• Little cloud cover
• Dry air that allows infrared radiation to escape freely

Humid regions, by contrast, cool much more slowly overnight because water vapour and clouds absorb and re‑emit infrared radiation back toward the surface.
So, deserts highlight what happens when the greenhouse effect is weak, not when it is absent or invalid.

Key references
·       Pierrehumbert, R. T. (2010). Principles of Planetary Climate. Cambridge: Cambridge University Press. https://www.cambridge.org/highereducation/books/principles-of-planetary-climate/5B5EEF0534CB6F69FB2E395DD21D3476#overview
·       Trenberth, K. E., J. T. Fasullo, and J. Kiehl, 2009: Earth’s Global Energy Budget. Bull. Amer. Meteor. Soc., 90, 311–324, https://doi.org/10.1175/2008BAMS2634.1.

4. Why is water vapour-the most abundant greenhouse gas-“ignored”?
Water vapour is not ignored. It is included explicitly in all climate models and accounts for roughly half of the natural greenhouse effect.
The difference is one of causation:

• CO₂ is a forcing: humans add it directly, and it accumulates for centuries.
• Water vapour is a feedback: its concentration is controlled by temperature. Warmer air holds more moisture; cooler air holds less.

Because water vapour typically remains in the atmosphere for only days to weeks, humans cannot increase it independently on climate timescales. Instead, CO₂‑driven warming increases water vapour, which then amplifies that warming.

Key reference

• Colman and Soden (2021). Water vapor and lapse rate feedbacks in the climate system, Reviews of Modern Physics, DOI: https://doi.org/10.1103/RevModPhys.93.045002

5. Do historical warm periods show that CO₂ is not causative?
Past warm periods such as the Minoan, Roman, and Medieval warm periods were real. However:

• They were driven mainly by changes in solar activity, volcanic activity, and ocean circulation
• Their timing and magnitude differed by region
• They were not globally synchronous

Large global syntheses show that while different regions warmed at different times, no pre‑industrial period shows the near‑global coherence of modern warming. Today’s warming is distinct in both spatial extent and rate, and it coincides with a rapid CO₂ increase large enough -on physical grounds alone-to explain the observed energy imbalance.

Key references

• Neukom, R., Steiger, N., Gómez-Navarro, J.J. et al. No evidence for globally coherent warm and cold periods over the preindustrial Common Era. Nature 571, 550–554 (2019). https://doi.org/10.1038/s41586-019-1401-2
• PAGES 2k Consortium. Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era. Nat. Geosci. 12, 643–649 (2019). https://doi.org/10.1038/s41561-019-0400-0

6. Was the Hockey Stick graph a hoax -or just wrong?
Although it is a common claim that the ‘hockey stick’ graph was shown to be a hoax in court this is NOT accurate. The Mann vs Ball case in Canada was dismissed on procedural grounds related to delay, not on scientific merit. The court did not rule on the validity of the hockey stick, nor did it declare it fraudulent. The original Hockey Stick reconstruction was broadly accurate and calling it a hoax is not supported by scientific evidence. The original late‑1990s Hockey Stick was one of the first quantitative reconstructions combining multiple climate proxies to estimate hemispheric‑scale temperatures over the last millennium. It used limited data and early statistical methods-but its central conclusion was clear: Recent decades are unusually warm compared with most of the previous millennium. Multiple independent assessments since then have shown that:

• The shape and conclusion of the Hockey Stick are robust
• Later reconstructions using more data and improved methods look very similar
• Some show even greater recent warming

The U.S. National Academies reviewed the controversy and concluded that the basic finding of anomalous recent warmth was supported by the evidence, even as methods continued to improve.

Key references

• National Academies of Sciences (2006), Surface Temperature Reconstructions for the Last 2,000 Years https://www.nae.edu/19579/19582/19649/25599/Surface-Temperature-Reconstructions-for-the-Last-2000-Years

Lastly, I thought I’d add some info about independent confirmation of recent human-driven climate warming by former sceptics through the Berkeley Earth Surface Temperature project, initiated specifically to investigate sceptical claims about temperature records. The project was founded by physicist Richard A. Muller, who initially shared concerns about data quality and bias. Berkeley Earth reanalysed virtually all available land‑temperature records, using transparent methods and open data. Their findings confirmed earlier datasets, including the conclusions consistent with the Hockey Stick.
Muller publicly acknowledged this outcome, writing: “Call me a converted skeptic. … Following an intensive research effort, I concluded that global warming was real and that the prior estimates of the rate of warming were correct.” — Richard A. Muller, New York Times, 28 July 2012
He further noted: “Our results turned out to be close to those published by prior groups.” In other words, when sceptical criticisms were tested using independent methods, they reinforced confidence in the original conclusions, rather than overturning them.

Key reference

• Berkeley Earth project documentation (2012–2013), https://berkeleyearth.org/data/

Bottom line

• The greenhouse effect is well‑established physics
• Water vapour is central but acts as a feedback
• Past climate variability is real but not a rebuttal to modern warming
• The Hockey Stick graph was broadly correct, and its conclusions have been repeatedly confirmed
• Modern climate science rests on multiple, independent lines of evidence, not any single graph or individual

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