Climate Change in the XXIst Century: Mechanisms and Predictions IGOR KHMELINSKII a and PETER STALLINGA b a FCT, DQF and CIQA Universidade do Algarve Campus de Gambelas, Faro PORTUGAL ikhmelin@ualg.pt b FCT, DEEI and CEOT Universidade do Algarve Campus de Gambelas, Faro PORTUGAL pjotr@ualg.pt Abstract: Recent experimental works demonstrated that the Antropogenic Global Warming (AGW) hypothesis, embodied in a series of Intergovernmental Panel on Climate Change (IPCC) global climate models, is erroneous. These works prove that atmospheric carbon dioxide contributes only very moderately to the observed warming, and that there is no climatic catastrophe in the making, independent on whether or not carbon dioxide emissions will be reduced. In view of these developments, we discuss climate predictions for the XXIst century. Based on the solar activity tendencies, a new Little Ice Age is predicted by the middle of this century, with significantly lower global temperatures. Key-Words: global warming, IPCC climate models, total solar irradiance, galactic cosmic rays, solar cycles, climate change, Little Ice Age 1 Introduction: IPCC climate scenarios are erroneous The terrestrial climate system is quite complex. A complete theory needs to account for the phenomena taking place on the Sun, which provides the energy in the form of electromagnetic radiation that puts the climate engine in motion, and the atmosphere and the oceans, that redistribute the energy, with biosphere and humanity affecting the amount of solar energy circulating in the climate system. The energy is eventually re-emitted into outer space in the form of infrared (IR) radiation, maintaining the climate system in an approximate dynamic equilibrium. Surface temperature T is one of the most important climatic variables, which affects the distribution and the very existence of all of the diverse life forms on land, including human civilization, dependent for its existence on availability of potable water and agricultural productivity. The existence of amenable surface temperatures depends on the greenhouse effect, caused by gases present in the atmosphere. The most important greenhouse gas is water vapour (H 2 O), followed by carbon dioxide (CO 2 ), methane (CH 4 ), ozone and halocarbons. These gases absorb IR radiation, that would otherwise immediately escape into space, reemitting part of it back towards the surface. Therefore, they provide some additional thermal insulation for the surface, resulting in the average surface temperature that is ca. 32 K (32 ºC) higher than it would be otherwise. Some 30 years ago, when the growth in atmospheric concentration of CO 2 , which we shall denote as [CO 2 ], caused by increased human use of fossil fuels, has coincided with the growth in average global temperature (global warming), concerns were risen that the observed warming may be caused by CO 2 , due to increased greenhouse effect, with possible adverse climatic consequences. These concerns led to the creation of the Intergovernmental Panel on Climate Change (IPCC), an entity under the UN, to evaluate risks of climate change caused by human activity. This entity produces reports, the latest of 2007, describing the current state of climate science as perceived by IPCC experts [1]. As it happens, the only evidence that ever indicated that global warming may be caused by growing atmospheric [CO 2 ] was that of the climate models. These are implemented in software, running on supercomputers, and first make use of real climate information to tune various parameters present in the models, attempting next to produce predictions/ projections on the future climate based on different scenarios of atmospheric [CO 2 ] evolution and other relevant human-generated perturbations, such as changes in land use. Climate models used by the Recent Researches in Energy & Environment ISBN: 978-960-474-274-5 26