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Revised draft (BK Dec 5, 2016 <br />This is another in a series of articles by the Orange County Commission for the Environment <br />(CFE). Each article highlights an environmental issue of interest to the residents of Orange <br />County. The CFE is a volunteer advisory board to the Board of County Commissioners. <br />Additional information can be found in the Orange County State of the Environment 2014 report <br />at r /commission for the environment.php <br />Climate Change (Part 2 of 2) <br />Orange County Commission for the Environment <br />Paleoclimate <br />Climate change in the distant past informs us about climate change today; that is, it <br />shows that CO2 drove climate change then as now. In fact, there is a strong link between <br />atmospheric CO2 and temperature throughout the Phanerozoic Eon, the past 550 million <br />years of earth history beginning with the Cambrian Period, a time of rapid diversification of <br />multi - celled life. During warm periods CO2 was high and when CO2 was low, long -lived and <br />widespread continental glaciation prevailed. <br />Perhaps the best ancient analog of modern climate change is the Paleocene - Eocene <br />Thermal Maximum (PETM), a 200,000 -year period of natural global warming that took <br />place 56 million years ago. The earth warmed approximately 11 OF over 20,000 years. <br />Today the globe is warming at least 10 times faster! <br />Because the PETM involved very rapid warming caused by an onslaught of GHGs, <br />the event can be used to predict potential effects of modern climate change. Among these <br />effects are: ocean acidification and circulation reversal, higher ocean temperatures and sea <br />levels, dissolution of calcifiers' shells, coral bleaching, and extinction events. <br />What is evident is that when CO2 changes were big and rapid (like today) the <br />consequences were catastrophic - -in some cases causing mass extinction. At least eight <br />major mass extinctions have been recognized. During these events a significant proportion <br />of the world's biota ( >50 %) were eliminated in geologically short amounts of time on the <br />order of tens of thousands to less than 1 million years. It can take millions of years for <br />biodiversity to recover. These extinctions occurred during times of major flood basalt <br />(lava) eruptions releasing huge volumes of CO2 accompanied by anoxia (oxygen deficiency), <br />euxinia (sulfidic conditions), and acidification of the surface ocean. One of the <br />