Abstract
We use a newly developed technique that is based on the information flow concept to investigate the causal structure between the global radiative forcing and the annual global mean surface temperature anomalies (GMTA) since 1850. Our study unambiguously shows one-way causality between the total Greenhouse Gases and GMTA. Specifically, it is confirmed that the former, especially CO2, are the main causal drivers of the recent warming. A significant but smaller information flow comes from aerosol direct and indirect forcing, and on short time periods, volcanic forcings. In contrast the causality contribution from natural forcings (solar irradiance and volcanic forcing) to the long term trend is not significant. The spatial explicit analysis reveals that the anthropogenic forcing fingerprint is significantly regionally varying in both hemispheres. On paleoclimate time scales, however, the cause-effect direction is reversed: temperature changes cause subsequent CO2/CH4 changes.
Highlights
We use a newly developed technique that is based on the information flow concept to investigate the causal structure between the global radiative forcing and the annual global mean surface temperature anomalies (GMTA) since 1850
The following phrase from the executive summary of Ch 10. of the recent IPPC-2013 assessment might serve for summarising the actual situation: “Uncertainties in forcings and in climate models’ temperature responses to individual forcings, and difficulty in distinguishing the patterns of temperature response due to greenhouse gases and other anthropogenic forcings prevent a more precise quantification of the temperature changes attributable to greenhouse gases”
The atmospheric CO2 content serves only as proxy for its radiative forcing and we examine in more detail the causal relations between the major climate forcings and GMTA
Summary
We use a newly developed technique that is based on the information flow concept to investigate the causal structure between the global radiative forcing and the annual global mean surface temperature anomalies (GMTA) since 1850. During the past five decades, the earth has been warming at a rather high rate ((1951–2012; 0.12 [0.08 to 0.14] °C per decade), International Panel of Climate Change, IPCC-2013)[1], resulting in a scientific and social concern This warming trend is observed in both field[2,3] and model data[4], and affects the atmosphere both over the land and over the ocean. The warming rate changes with time, raising questions regarding the causes underlying the observed trends[5] Another problem is the relatively large uncertainty in the different external forcing components[6,7,8,9] that leads to a rather large scatter in the global climate simulations and may have overestimated recent global warming[10,11]. Recent updates based on multimodel analysis[14,15,16] confirm that the primary components of external forcing over the past century are human-caused increases in www.nature.com/scientificreports/
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