CO2 Affects Temperature but Does CO2 Drive Climate?

January 1, 2025 rjdavison

OPS-80 – CO2 Affects Temperature But Does CO2 Drive Climate Download PDF

OPS-80 To start with I would like to wish that everyone’s New Year is a Happy, Healthy, and Prosperous one! 2024 was a good year for climate realism, looking for 2025 to be even better.

A simple question with a simple, but complicated answer. The answer is effectively NO! While CO₂ is contributing to temperature changes, its effects are lost in the natural variation. Many other much more dominant forcings overwhelm the small CO₂ contributions that may be present. To understand CO₂’s contributions, one must understand CO₂’s Climate Sensitivity (CCS). Given that the current crop of climate models (CMIP6) uses a range of 1.8 to 5.7 °C, we just might have to conclude that CCS is not settled science. And given that all the models are self-acknowledged to “run way too hot” (even when they use realistic emission scenarios like ssp2-4.5), we can easily surmise that the CCS is somewhere less than 1.8 °C.

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I was recently presented a progressively more detailed plot of the Phanerozoic (Figure 1 in the detailed discussion attached and like the one I produced a few years ago in my CSS-15 – Phanerozoic – Progressive Detail post) as proof that CO₂ was driving the climate (and apparently always has been). While the CO₂ concentrations and Temperatures do generally move in similar directions, there are many more and more powerful forcings in play than just CO₂. If we know CO₂’s Climate Sensitivity, we can back out how much of the temperature change is due to CO₂. We can start with the assumption (dubious at best) that all the warming (1.07 °C according to the IPCC’s 2021 AR6 report) since 1850 (the pre-industrial era) is due to the 135 ppm increase in atmospheric CO₂ concentrations. That equates to a CCS of 1.86 °C (consistent with the 1.94 °C that can be pulled from Figure 1 (Era 1), despite the poor resolution). A CCS of ±0.8 °C is much more practical and would fix many of those pesky accuracy issues that are currently plaguing the CMIP6 climate models and would even allow them the capability of accurately hind casting the temperatures pre-1850. The rationale for 0.8 °C is included in the detailed discussion.

Over the modern temperature record, the models have been programmed to ignore and/or minimize the natural contributions (primarily solar activity, directly and indirectly). Including a more representative reconstruction of solar activity and other factors like Urban Heat Island (UHI) effects easily drops the CCS down from ±1.9 °C to ±0.8 °C. At 1.94 °C, CO₂’s contribution levels for Era 2 to Era 6 in Figure 1 range from 15% (Era 4) to 36% (Era 5). Significant, but not the dominant reason for the temperature changes (12.53 and 5.40 °C, respectively). That establishes the upper limits of CO₂ contribution. For the bulk of the Phanerozoic (Era 6, 86.8% of the history shown) CO₂’s contribution levels are at 20%. If the CCS is 0.8 °C, the CO₂ contribution levels drop to 6% for Era 4, 15% for Era 5, and 8% for Era 6.

So no, CO₂, while contributing to temperature changes, is not driving the climate. Over the Modern Temperature Record (1850 to the present), CO₂’s contribution is likely around 40% (0.4 °C of the 1.07 °C temperature rise based on a CCS of 0.8 °C).

What is the main difference between a CCS of 1.9 °C and 0.8 °C? The climate models have programmed in just one of the 40 available Total Solar Irradiance (TSI) reconstructions that happens to coincide with their narrative. As mentioned previously, even the models using the low-end CCS run too hot, setting an upper limit for the CCS at 1.8 °C. Using a more realistic TSI reconstruction and incorporating the UHI effect, easily drops the CCS into the 0.8 °C range. For some additional discussion on the TSI reconstructions, go to the Center for Environmental Research and Earth Sciences (CERES) site, www.ceres-science.com.

On these time scales (hundreds to thousands of years), solar activity, ocean cycles, electromagnetic field changes, solar wind fluctuations, Cosmic Ray Flux (CRF), cloud albedo, etc. and yes even CO₂ are contributing to climate and weather changes. On the scale of tens to hundreds of thousands of years, the Milankovitch Cycles are driving the climate (both temperature and CO₂). Expanding the time frame out to millions and tens of millions of years, brings plate tectonics (major ocean cycle disruptions), natural CO₂ sequestration (carbonate rocks and coals) and some celestial impacts into the climate equation. On the longer periods (hundreds of millions of years) our position in the Milky Way Galaxy becomes a factor. When we are in one of the arms, we are exposed to a significantly higher CRF, which leads to a higher cloud albedo and deep ice ages. We entered the Sagittarius-Carina arm and the current ice age (as defined by permanent ice at the poles) at just over 30 million years ago. We are lucky enough to be living through the Holocene interglacial warm period, but we will be back into a deep ice age sometime over the next few thousand years.

The subject is a lot more complicated than the simplistic, unscientific All CO₂, All the Time narrative. Relying on the Modern Temperature Record for proof of climate change is not particularly sound ‘climate science’, given the short time frame and the flat CO₂ concentrations and declining sea levels and temperatures, that dominated the early 1800s. And why did temperatures fluctuate significantly over the pre-MTR Holocene for 10,000+ years despite a virtually flat CO₂ concentration? How can the current CMIP6 models be expected to model the pre-MTR Holocene correctly, when they are effectively programmed to respond almost exclusively to CO₂ changes? All food for thought!

OPS-80 – Detailed Discussion Download PDF

Here are some additional articles/papers/posts that provide additional context to this discussion.

Earth’s Climate System – Salawitch, R. et al (2017)

https://link.springer.com/chapter/10.1007/978-3-319-46939-3_1

An astronomically dated record of Earth’s climate and its predictability over the last 66 million years – Westerhold et al (2020)

https://www.researchgate.net/publication/344230305_An_astronomically_dated_record_of_Earth%27s_climate_and_its_predictability_over_the_last_66_million_years

Naval Research Labs’ NRLTSI2 TSI Reconstruction

https://lasp.colorado.edu/lisird/data/nrl2_files

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