The Earth is a Planet Too!

[摘要] When the solar system formed, the sun was 30 dimmer than today and Venus had an ocean. As the sun brightened, a runaway greenhouse effect caused the Venus ocean to boil away. At times when Earth was younger, the sun less bright, and atmospheric CO2 less, Earth froze over (snowball Earth). Earth is in the sweet spot today. Venus is closer to sun than Earth is, but cloud-covered Venus absorbs only 25 of incident sunlight, while Earth absorbs 70. Venus is warmer because it has a thick carbon dioxide atmosphere causing a greenhouse effect of several hundred degrees. Earth is Goldilocks choice among the planets, the one that is just right for life to exist. Not too hot. Not too cold. How does the Earth manage to stay in this habitable range? Is there a Gaia phenomenon keeping the climate in bounds? A nice idea, but it doesnt work. Today, greenhouse gas levels are unprecedented compared to the last 450,000 years.

[发布日期] 2014-07-21

[学科分类] 大气科学