Abstract
We use data on the following climate variables for the period of the last 798 thousand years: global ice volume (Icet), atmospheric carbon dioxide level (CO2,t), and Antarctic land surface temperature (Tempt). Those variables are cyclical and are driven by the following strongly exogenous orbital variables: eccentricity of the Earth’s orbit, obliquity, and precession of the equinox. We introduce score-driven ice-age models which use robust filters of the conditional mean and variance, generalizing the updating mechanism and solving the misspecification of a recent climate–econometric model (benchmark ice-age model). The score-driven models control for omitted exogenous variables and extreme events, using more general dynamic structures and heteroskedasticity. We find that the score-driven models improve the performance of the benchmark ice-age model. We provide out-of-sample forecasts of the climate variables for the last 100 thousand years. We show that during the last 10–15 thousand years of the forecasting period, for which humanity influenced the Earth’s climate, (i) the forecasts of Icet are above the observed Icet, (ii) the forecasts of CO2,t level are below the observed CO2,t, and (iii) the forecasts of Tempt are below the observed Tempt. The forecasts for the benchmark ice-age model are reinforced by the score-driven models.
Highlights
According to Intergovernmental Panel on Climate Change (2021), compared to the period of 1850–1900, the Earth’s global surface temperature for the period of 2081–2100 will very likely rise by 3.3 to 5.7 °C under the worst-case scenario, which implies dramatic consequences on the nature and wildlife in terrestrial, wetland, and ocean ecosystems, and on humanity with respect to food and water security, migration, health, higher risk of conflict worldwide, reduction of global economic product, and a possible collapse of the current societal organization
For the last 10–15 thousand years of the forecasting period, we find that: (i) the forecasts of global ice volume are above the observed global ice volume, (ii) the forecasts of the atmospheric CO2 level are below the observed CO2 level, and (iii) the forecasts of Antarctic land surface temperature are below the observed Antarctic land surface temperature
The data source of Antarctic land surface temperature Tempt is in the work of Jouzel et al (2007), in which temperature data were obtained within the European Project for Ice Coring in Antarctica (EPICA) at the Concordia Station (Dome C), using deuterium δDice measurements from the surface down to 3259.7 m
Summary
According to Intergovernmental Panel on Climate Change (2021), compared to the period of 1850–1900, the Earth’s global surface temperature for the period of 2081–2100 will very likely rise by 3.3 to 5.7 °C under the worst-case scenario, which implies dramatic consequences on the nature and wildlife in terrestrial, wetland, and ocean ecosystems, and on humanity with respect to food and water security, migration, health, higher risk of conflict worldwide, reduction of global economic product, and a possible collapse of the current societal organization. Climate change is partly due to the influence of humanity, which started approximately 10–15 thousand years ago, by commencing agricultural activities such as cultivating plants and livestock (Ruddiman 2005). The atmospheric CO2 levels and land surface temperature are related to melting glaciers and sea ice. We name the climate–econometric models of those variables as ice-age models, as per the work of Castle and Hendry (2020). During the 4.5 billion-year history of the Earth, the ice volume, atmospheric CO2 , and land surface temperature simultaneously
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