Pontus Lurcock and Fabio Florindo
Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.
Joan Martí Molist
Volcanoes represent complex geological systems capable of generating many dangerous phenomena. To evaluate and manage volcanic risk, we need first to assess volcanic hazard (i.e., identify past volcanic system behavior to infer future behavior. This requires acquisition of all relevant geological and geophysical information, such as stratigraphic studies, geological mapping, sedimentological studies, petrologic studies, and structural studies. All this information is then used to elaborate eruption scenarios and hazard maps. Stratigraphic studies represent the main tool for the reconstruction of past activity of volcanoes over time periods exceeding their historical record. This review presents a systematic approach to volcanic hazard assessment, paying special attention to reconstruction of past eruptive history. It reviews concepts and methods most commonly used in long- and short-term hazard assessment and analyzes how they help address the various serious consequences derived from the occurrence (and nonoccurrence in some crisis alerts) of volcanic eruptions and related phenomena.
This article discusses the importance of assessing and estimating the risk of earthquakes. It begins with an overview of earthquake prediction and relevant terms, namely: earthquake hazard, maximum credible earthquake magnitude, exposure time, earthquake risk, and return time. It then considers data sources for estimating seismic hazard, including catalogs of historic earthquakes, measurements of crustal deformation, and world population data. It also examines ways of estimating seismic risk, such as the use of probabilistic estimates, deterministic estimates, and the concepts of characteristic earthquake, seismic gap, and maximum rupture length. A loss scenario for a possible future earthquake is presented, and the notion of imminent seismic risk is explained. Finally, the chapter addresses errors in seismic risk estimates and how to reduce seismic risk, ethical and moral aspects of seismic risk assessment, and the outlook concerning seismic risk assessment.