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Conclusions

Data assimilation leverages paleotemperature proxy information and model simulations, capitalizing on both a large catalog of geological data as well as our best physical understanding of Phanerozoic climates (Fig. 1). The resulting product, PhanDA, is a statistically robust and internally consistent reconstruction of GMST spanning the past 485 million years and indicates that Earth’s temperature has varied more dynamically than previously thought (Fig. 2). We divide the record into five quantiles, or climate states (Fig. 3), and use these distinctions to demonstrate that, independent of time and throughout the Phanerozoic, GMSTs within each climate state are associated with similar LTGs. In addition to the expected polar amplification, PhanDA indicates a large range in tropical temperatures between the five climate states (22° to 42°C).

PhanDA GMST exhibits a strong relationship with atmospheric CO2 concentrations (Fig. 4), demonstrating that CO2 has been the dominant forcing controlling global climate variations across the Phanerozoic. However, because solar luminosity has also changed through time, the relationship is rather enigmatic; long-term changes in planetary albedo or changes in trace greenhouse gas concentrations may help to resolve the discrepancy. The CO2–GMST relationship also indicates a relatively consistent AESS of ~8°C across the Phanerozoic. This suggests that Phanerozoic GMST is highly predictable on multimillion-year timescales if CO2 concentrations are known, but that our understanding of how forcings and feedbacks on deep timescales balance—or enhance—one another is incomplete.
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Note that the variations in GMST happen gradually over millions of years...and as mentioned , are strongly influenced by atmospheric CO2 concentrations. Our current Doubling of average CO2 concentration has occurred in just over 100 years...or 0.0001 of just 1M yrs...undeniably due to the burning of Finite Fossil Fuels.

It's not the Planet we're concerned about...it's the human population living on it...i.e. how will this rapid increase in GMST (see Dr. Roy Spencer's Global Temperature Data chart) affect the living and food growing conditions of today's humans? btw, you might want to ask Floridians how they feel about the next Cat 4 Hurricane about to beat down on them.