The Relationship between Atmospheric Carbon Dioxide Concentration and Global Temperature for the Last 425 Million Years

Abstract

Assessing human impacts on climate and biodiversity requires an understanding of the relationship between the concentration of carbon dioxide (CO 2 ) in the Earth's atmosphere and global temperature (T). Here I explore this relationship empirically using comprehensive, recently-compiled databases of stable-isotope proxies from the Phanerozoic Eon (~540 to 0 years before the present) and through complementary modeling using the atmospheric absorption/transmittance code MODTRAN. Atmospheric CO 2 concentration is correlated weakly but negatively with linearly-detrended T proxies over the last 425 million years. Of 68 correlation coefficients (half non-parametric) between CO 2 and T proxies encompassing all known major Phanerozoic climate transitions, 77.9% are non-discernible (p > 0.05) and 60.0% of discernible correlations are negative. Marginal radiative forcing (∆RF CO2 ), the change in forcing at the top of the troposphere associated with a unit increase in atmospheric CO 2 concentration, was computed using MODTRAN. The correlation between ∆RF CO2 and linearly-detrended T across the Phanerozoic Eon is positive and discernible, but only 2.6% of variance in T is attributable to variance in ∆RF CO2 . Of 68 correlation coefficients (half non-parametric) between ∆RF CO2 and T proxies encompassing all known major Phanerozoic climate transitions, 75.0% are non-discernible and 41.2% of discernible correlations are negative. Spectral analysis, autoand cross-correlation show that proxies for T, atmospheric CO 2 concentration and ∆RF CO2 oscillate across the Phanerozoic, and cycles of CO 2 and ∆RF CO2 are antiphasic. A prominent 15 million-year CO 2 cycle coincides closely with identified mass extinctions of the past, suggesting a pressing need for research on the relationship between CO 2 , biodiversity extinction, and related carbon policies. This study demonstrates that changes in atmospheric CO 2 concentration did not cause temperature change in the ancient climate.

The Antarctic Centennial Oscillation: A Natural Paleoclimate Cycle in the Southern Hemisphere That Influences Global Temperature

“…This NGW hypothesis merits and requires further research as an alternative to the AGW hypothesis. As established by previous research [3], however, the possibility that contemporary global warming results from a natural climate cycle, rather than from anthropogenic emissions of CO 2 , may not lessen the urgency to consider limiting anthropogenic CO 2 emissions. Peaks in atmospheric CO 2 concentration in the ancient climate [3] coincide closely with peaks in past mass extinctions [83], mediated perhaps by acidification of ocean water [84,85].…”

“…Spectral analysis, for example, which is based on Fourier transformation, is technically applicable only to stationary time series. Our study shows that climate data do not necessarily comprise a stationary time series, yet spectral analysis is used almost universally in climate science, including in most of the references we cite here (e.g., [2] (Figure 12, p. 123), [3] (Figures 7 and 10), [4] (Figure 4, p. 689), [5] (Figure 12, p. 14), [6] (Figure 2b,d,f, p. 509), etc. Our study suggests the need for a comprehensive expert review of methodological approaches to the analysis of climate data in view of potential non-stationarity.…”

“…Recent research shows, however, that neither atmospheric CO 2 nor marginal radiative forcing by CO 2 is generally correlated discernibly with global temperature over the past 425 million years [3]. Therefore, neither atmospheric CO 2 nor marginal radiative forcing by CO 2 caused temperature change in the ancient climate [3]. The same study showed that contemporary marginal radiative forcing by atmospheric CO 2 has declined by approximately two-thirds since the beginning of the Industrial Age owing to the well-known logarithmic relationship between radiative forcing and atmospheric CO 2 concentration [3].…”

“…It has been considered widely that atmospheric carbon dioxide (CO 2 ) emitted by human activities is responsible for the contemporary global warming signal. Recent research shows, however, that neither atmospheric CO 2 nor marginal radiative forcing by CO 2 is generally correlated discernibly with global temperature over the past 425 million years [3]. Therefore, neither atmospheric CO 2 nor marginal radiative forcing by CO 2 caused temperature change in the ancient climate [3].…”

“…Global temperature has oscillated at least since the beginning of the Phanerozoic Eon 542 million years (My) ago, manifest as long climate cycles that repeat with a period of 135-150 My [1][2][3]. Faster and smaller temperature oscillations are superimposed on the cooling phase of the most recent long cycle beginning at least~55 million years before present (Mybp) [4], forming the earliest Marine Isotope a possible alternative explanation in the form of a natural climate cycle that arises in Antarctica, propagates northward to influence global temperature, and peaks on a predictable centennial timetable.…”