Year: 2013
Type: dissertation
Abstract: Greenhouse gas warming, internal climate variability and aerosol climate effects are studied and the importance to understand these key processes and being able to separate their influence on the climate is discussed. Aerosol-climate model ECHAM5-HAM and the COSMOS millennium model consisting of atmospheric, ocean and carbon cycle and land-use models are applied and results compared to measurements. Topics at focus are climate sensitivity, quasiperiodic variability with a period of 50-80 years and variability at other timescales, climate effects due to aerosols over India and climate effects of northern hemisphere mid- and high-latitude volcanic eruptions. The main findings of this work are 1) pointing out the remaining challenges in reducing climate sensitivity uncertainty from observational evidence, 2) estimates for the amplitude of a 50-80 year quasiperiodic oscillation in global mean temperature ranging from 0.03 K to 0.17 K and for its phase progression as well as the synchronising effect of external forcing, 3) identifying a power law shape S(f) ∝ f−α for the spectrum of global mean temperature with α ∼ 0.8 between multidecadal and El Nino timescales with a smaller exponent in modelled climate without external forcing, 4) separating aerosol properties and climate effects in India by season and location 5) the more efficient dispersion of secondary sulfate aerosols than primary carbonaceous aerosols in the simulations, 6) an increase in monsoon rainfall in northern India due to aerosol light absorption and a probably larger decrease due to aerosol dimming effects and 7) an estimate of mean maximum cooling of 0.19 K due to larger northern hemisphere mid- and high-latitude volcanic eruptions. The results could be applied or useful in better isolating the human-caused climate change signal, in studying the processes further and in more detail, in decadal climate prediction, in model evaluation and in emission policy design in India and other Asian countries.
Source: Työväentutkimus Vuosikirja
Author: Svante Henriksson
Institution: Finnish Meteorological Institute
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W1556533104