SCIENCE of
CLIMATE CHANGE

International Journal of Science and Philosophy

How Much CO2 and the Sun Contribute to Global Warming: Comparison of Simulated Temperature Trends with Last Century Observations

Author

  • Hermann Harde, Helmut-Schmidt-University, Holstenhofweg 85, 22043 Hamburg, Germany

Abstract

The Intergovernmental Panel on Climate Change classifies the human influence on our climate as extremely likely to be the main reason of global warming over the last decades. Particularly anthropogenic emissions of carbon dioxide are made responsible for the observed temperature changes, while any natural forcings are almost completely excluded. However, detailed own calculations with an advanced energy-radiation-balance model indicate that the temperature increase and its variations over the last 140 years can much better be explained by additionally including solar radiative forcing and its amplification by induced cloud cover changes. We present simulations based on different time series of the total solar irradiance and compare them with composed land-ocean-surface temperature measurements of the Northern Hemisphere. From these simulations we follow that CO2 should not have contributed more than about one third to global warming over the last century, while solar variations over this period can well explain two thirds of the increase.

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How Much CO2 and the Sun Contribute to Global Warming: Comparison of Simulated Temperature Trends with Last Century Observations

Description

Author

  • Hermann Harde, Helmut-Schmidt-University, Holstenhofweg 85, 22043 Hamburg, Germany

Abstract

The Intergovernmental Panel on Climate Change classifies the human influence on our climate as extremely likely to be the main reason of global warming over the last decades. Particularly anthropogenic emissions of carbon dioxide are made responsible for the observed temperature changes, while any natural forcings are almost completely excluded. However, detailed own calculations with an advanced energy-radiation-balance model indicate that the temperature increase and its variations over the last 140 years can much better be explained by additionally including solar radiative forcing and its amplification by induced cloud cover changes. We present simulations based on different time series of the total solar irradiance and compare them with composed land-ocean-surface temperature measurements of the Northern Hemisphere. From these simulations we follow that CO2 should not have contributed more than about one third to global warming over the last century, while solar variations over this period can well explain two thirds of the increase.

Introduction

The Fifth and Sixth Assessment Report (AR5 and AR6) [1, 2] of the Intergovernmental Panel on Climate Change (IPCC) announced new evidence of an anthropogenic climate change based on many independent scientific analyses from observations of the climate system, paleoclimate archives, theoretical studies of climate processes, and simulations using climate models. In these reports the IPCC classifies the human influence as extremely likely to be the dominant cause of the observed warming since the mid-20th century (e.g., AR5-WG1-SPM-D3), while contributions from natural forcings and internal variability would only likely be in the range of −0.1°C to 0.1°C. Particularly increasing emissions of carbon dioxide (CO2) over the last century are made responsible for this change, and the Equilibrium Climate Sensitivity (ECS) as a measure for the Earth’s temperature increase at doubled CO2 concentration in the atmosphere is specified with an assessed best estimate of 3°C and a likely range of 2.5°C to 4°C (high confidence, AR6-WG1-SPM, A.4.4) – acronyms see Annex.