Dr D Weston Allen, MBBS, FRACGP, Grad Dip Phys Med
Man-made climate change is real, but natural climate change can be worse and faster. Atmospheric carbon dioxide (CO2) gradually fell from about 3,000 parts per million (ppm) 200 million years ago to only 180ppm a million years ago, as carbon was naturally sequestered, and Earth became very cold, dry and dusty. Recurring orbital cycles trigger interglacial warm periods such as our present Holocene which began nearly twelve thousand years ago. Warming oceans release CO2, pushing atmospheric levels up over 280ppm, which helps plants thrive in a warmer wetter world. The previous interglacial about 120,000 years ago was much warmer than now. As temperatures fell over ten degrees Celsius (10⁰C) during the last ice-age, CO2 fell to 180ppm. Humanity thrived during the warm Holocene Climatic Optimum but suffered and endured worse cyclonic floods and prolonged droughts during the recent Little Ice Age, especially when solar activity declined during the Maunder Minimum (1645-1715 AD).
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