LIMITS OF ATMOSPHERIC PCO2 IN RECONSTRUCTING ANCIENT AND PREDICTING FUTURE CLIMATE: THE ROLES OF GLOBAL REFLECTANCE AND CONTINENT DISTRIBUTION

The dominant models for ancient and future global temperatures draw on Svante Arrhenius’ 1896 insights. He concluded CO₂ was a key temperature driver and anticipated the modern climate catastrophe by calculating the effect of rising industrial CO₂ emissions. The link from the late-19^th century of rising temperature with ever higher pCO₂ based on atmospheric and ice core samples substantiates his conclusions and illustrates warming by the greenhouse model. Greenhouse warming will accelerate with increasing pCO₂ (ca. 2.5 ppm/yr, 340‒405 ppm over 1980‒2019) and feed-backs that increase greenhouse gas concentration (e.g., permafrost melting with CO₂ and methane release, slowed CO₂ storage by the biotic effects of oceanic acidification and drying-out of temperate forests, lower CO₂ uptake by warming oceans). Arrhenius showed the marginal radiative forcing of CO₂ was highest at 200 ppm, fell at higher pressures, with the “warming effect” effectively capped at 1,000 ppm―a value likely reached in less than 200 years with feedbacks and humanity’s uncertain response. But, the warming rate will increase as non-greenhouse factors will come to dominate Earth’s temperature by lowering of its albedo (reflectivity). Thus, melting of ca. 50% of reflective Arctic Ocean pack ice over 30 yr has increased global warming rate by ca. 25 %―a rate that will accelerate with complete global ice loss. Ice melt accelerates the eustatic rise rate by 3.1 mm/yr. over each previous year, with heat absorbing and higher insolation water ultimately covering ca. 15% of the more reflective land. An adequate global temperature model must incorporate 1) analysis that shows Phanerozoic temperatures independent/slightly negatively correlated with the very high pCO₂ values of the GEOCARB model (levels sometimes incompatible with terrestrial metazoans and many embryophytes), 2) the rapid pCO₂ fall in the Devonian with no significant temperature decrease, and 3) the lower “warming effect” above 1,000 ppm. Global temperature models must include non-greenhouse (i.e., hyperwarming) factors as changed albedo with eustatic rise/fall and ice loss/growth, lower vs higher latitude continent distributions, and presence of a polar continent/restricted polar ocean.