Past Climates or

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Past Climates or

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1. Past Climates or Paleoclimatology

2. Estimated Phanerozoic Temperatures (14° is Today; 16° is Critical and 18° is Catastrophic for Humans)

3. Generalized Climates for the Past 3 Billion Years The diagram shows only the dominant climatic regime in Earth’s history. That history has been dominated by Hot Houses with temperatures well above today’s and little or no ice on Earth. Ice Houses consist of alternating glacial and interglacial periods. They have been relatively rare throughout most of geologic history. We are now in an interglacial period of an Ice House. Not shown are limited cold periods in some Hot Houses and limited warm periods in some Ice Houses. There have only been three significant Ice Houses in the past 540 million years. We are currently in the third. The diagram shows only the dominant climatic regime in Earth’s history. That history has been dominated by Hot Houses with temperatures well above today’s and little or no ice on Earth. Ice Houses consist of alternating glacial and interglacial periods. They have been relatively rare throughout most of geologic history. We are now in an interglacial period of an Ice House. Not shown are limited cold periods in some Hot Houses and limited warm periods in some Ice Houses. There have only been three significant Ice Houses in the past 540 million years. We are currently in the third.

4. Climate Change During Past 180 Million Years Changes in the Earth’s temperature through time. Red areas are warmer and dark blue areas are colder. The temperatures are referenced to the 1951-1980 average global temperature of 14° C. (Left) The top diagram spans the period from about the lower Mesozoic Era to the present shown at the bottom of the previous slide. The two bottom diagrams are successive enlargements of the present “Ice House” during the Pleistocene and Holocene Epochs. (Right) The top diagram shows the end of the last ice age and the present interglacial period (Holocene). Each of the enlargements show successively more detail including current global warming. All of human evolution has occurred in an Ice House and all of civilization has occurred in the present interglacial period (the Holocene). Modified from Cook et al., 1991.Changes in the Earth’s temperature through time. Red areas are warmer and dark blue areas are colder. The temperatures are referenced to the 1951-1980 average global temperature of 14° C. (Left) The top diagram spans the period from about the lower Mesozoic Era to the present shown at the bottom of the previous slide. The two bottom diagrams are successive enlargements of the present “Ice House” during the Pleistocene and Holocene Epochs. (Right) The top diagram shows the end of the last ice age and the present interglacial period (Holocene). Each of the enlargements show successively more detail including current global warming. All of human evolution has occurred in an Ice House and all of civilization has occurred in the present interglacial period (the Holocene). Modified from Cook et al., 1991.

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