The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change

The climate system of the Earth is endowed with a moderately strong greenhouse effect that is characterised by non-condensing greenhouse gases (GHGs) that provide the core radiative forcing. Of these, the most important is atmospheric CO 2 . There is a strong feedback contribution to the greenhouse effect by water vapour and clouds that is unique in the solar system, exceeding the core radiative forcing due to the non-condensing GHGs by a factor of three. The significance of the non-condensing GHGs is that once they have been injected into the atmosphere, they remain there virtually indefinitely because they do not condense and precipitate from the atmosphere, their chemical removal time ranging from decades to millennia. Water vapour and clouds have only a short lifespan, with their distribution determined by the locally prevailing meteorological conditions, subject to Clausius–Clapeyron constraint. Although solar irradiance is the ultimate energy source that powers the terrestrial greenhouse effect, there has been no discernable long-term trend in solar irradiance since precise monitoring began in the late 1970s. This leaves atmospheric CO 2 as the effective control knob driving the current global warming trend. Over geological time scales, volcanoes are the principal source of atmospheric CO 2 , and the weathering of rocks is the principal sink, with the biosphere participating as both a source and a sink. The problem at hand is that human industrial activity is causing atmospheric CO 2 , to increase by 2 ppm yr −1 , whereas the interglacial rate has been 0.005 ppm yr −1 . This is a geologically unprecedented rate to turn the CO 2 climate control knob. This is causing the global warming that threatens the global environment. Keywords: carbon dioxide, greenhouse effect, radiative forcing, climate change, global warming (Published: 27 November 2013) Citation: Tellus B 2013, 65 , 19734, http://dx.doi.org/10.3402/tellusb.v65i0.19734 This publication is part of a Thematic Cluster with papers presented at a conference held in Stockholm 21 - 23 May 2012, to honor the late Professor Bert Bolin for his outstanding contributions to climate science and his efforts to create a dialogue between policy makers and the scientific community. All papers within the cluster will be published online as soon as they have been accepted for publication. When all papers belonging to the cluster have been published, they will be summarized with a foreword describing the background and scope of the conference. Read the other papers from this thematic cluster here