Less Aerosols Cause Global Warming in the Last Two Decades

In most climate models, warming in global mean surface temperature (GMST) in the last two decades is mainly attributed to rising CO2. Here we present observed data of regional and global upper stratosphere temperature (UST) and surface temperature and of various climate drivers including greenhouse gases (GHGs), ozone, aerosols, solar variability, snow cover extent, and sea ice extent (SIE), combined with calculations of GMST by a conceptual physics model. We strikingly found warming trends of 0.8(+/-0.6) and 0.7(+/-0.2) K/decade in UST at altitudes of 35-40 km in the Arctic and Antarctic respectively and no significant trends over non-polar regions since 2002. Correspondingly, surface temperatures exhibit cooling trends in the Antarctic since 2002 and in the Arctic since 2016 when the SIE started to stabilize, no trend in the tropics, and warming trends at Southern and Northern mid-latitudes respectively. The latter warming causes the recent rise in GMST, which is well explained by the positive radiative forcings of aerosols and ozone associated with improved air quality. According to well-recognized climate models, the observed UST trends provide fingerprints of decreasing (no significant increase) in total GHG effect in polar (non-polar) regions. A coherent global phenomenon observed in both UST and surface temperature has emerged, which agrees well with calculated results by the warming model based on halogen-containing GHGs (halo-GHGs). With observations of rapidly lowered aerosol loading, projected halo-GHGs and stopped Arctic amplification, this study leads to a striking prediction of a GMST reversal, which will likely occur within next 5-10 years.