Privileged Planet: factors controlling climate (Introduction)

by David Turell , Thursday, July 23, 2020, 19:39 (1371 days ago) @ David Turell

Worth downloading and quick skimming to see moving figures:

https://www.quantamagazine.org/how-earths-climate-changes-naturally-and-why-things-are-...

"The sun has been dimming slightly for the last half-century while the Earth heats up, so global warming cannot be blamed on the sun.

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"Ilopango triggered a roughly 2 degree Celsius drop that lasted 20 years. More recently, the eruption of Pinatubo in the Philippines in 1991 cooled the global climate by 0.6 degrees Celsius for 15 months.

"Volcanic sulfur in the stratosphere can be disruptive, but in the grand scale of Earth’s history it’s tiny and temporary.

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"...the El Niño–Southern Oscillation, involves circulation changes in the tropical Pacific Ocean on a time frame of two to seven years that strongly influence rainfall in North America. The North Atlantic Oscillation and the Indian Ocean Dipole also produce strong regional effects. Both of these interact with the El Niño–Southern Oscillation.

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"Earth’s orbit wobbles as the sun, the moon and other planets change their relative positions. These cyclical wobbles, called Milankovitch cycles, cause the amount of sunlight to vary at middle latitudes by up to 25% and cause the climate to oscillate.

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'Though the sun’s brightness fluctuates on shorter timescales, it brightens overall by 0.009% per million years, and it has brightened by 48% since the birth of the solar system 4.5 billion years ago.

"Clement conditions in the second half of Earth’s existence, despite a brightening sun, do not create a paradox: Earth’s weathering thermostat counteracts the effects of the extra sunlight, stabilizing Earth’s temperature.

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"The main control knob for Earth’s climate through deep time has been the level of carbon dioxide in the atmosphere, since carbon dioxide is a long-lasting greenhouse gas that blocks heat that tries to rise off the planet.

"Each year, the burning of fossil fuels emits about 100 times more carbon dioxide than volcanoes emit — too much too fast for oceans and weathering to neutralize it, which is why our climate is warming and our oceans are acidifying.

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"Earlier, in the Jurassic and Cretaceous periods, dinosaurs roamed Antarctica because enhanced volcanic activity, in the absence of those mountain chains, sustained carbon dioxide levels around 1,000 parts per million, compared to 415 ppm today. The average temperature of this ice-free world was 5 to 9 degrees Celsius warmer than now, and sea levels were around 250 feet higher.

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"The rearrangement of land masses on Earth’s crust can slowly shift the weathering thermostat to a new setting.

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"The Earth Impact Database recognizes 190 craters with confirmed impact on Earth so far. None had any discernable effect on Earth’s climate except for the Chicxulub impact, which vaporized part of Mexico 66 million years ago, killing off the dinosaurs. Computer modeling suggests that Chicxulub blasted enough dust and sulfur into the upper atmosphere to dim sunlight and cool Earth by more than 20 degrees Celsius, while also acidifying the oceans.

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"Occasionally, the evolution of new kinds of life has reset Earth’s thermostat. Photosynthetic cyanobacteria that arose some 3 billion years ago, for instance, began terraforming the planet by emitting oxygen. As they proliferated, oxygen eventually rose in the atmosphere 2.4 billion years ago, while methane and carbon dioxide levels plummeted. This plunged Earth into a series of “snowball” climates for 200 million years.

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"In the end-Permian event 252 million years ago, which wiped out 81% of marine species, underground magma ignited Siberian coal, drove up atmospheric carbon dioxide to 8,000 parts per million and raised the temperature by between 5 and 9 degrees Celsius. The more minor Paleocene-Eocene Thermal Maximum event 56 million years ago cooked methane in North Atlantic oil deposits and funneled it into the sky, warming the planet by 5 degrees Celsius and acidifying the ocean"

Comment: A complex of activities evolved the Earth which made it comfortable for us today.