venus's atmosphere has much more carbon dioxide than earth's because of a runaway greenhouse effect.
venus's atmosphere has much more carbon dioxide than earth's because of a runaway greenhouse effect.
venus's atmosphere has much more carbon dioxide than earth's because?
a runaway greenhouse effect
a runaway greenhouse effect involving carbon dioxide and water vapor may have occurred on venus. in this scenario, early venus may have had a global ocean if the outgoing thermal radiation was below the simpson-nakajima limit but above the moist greenhouse limit. as the brightness of the early sun increased, the amount of water vapor in the atmosphere increased, increasing the temperature and consequently increasing the evaporation of the ocean, leading eventually to the situation in which the oceans boiled, and all of the water vapor entered the atmosphere. this scenario helps to explain why there is little water vapor in the atmosphere of venus today. if venus initially formed with water, the runaway greenhouse effect would have hydrated venus' stratosphere, and the water would have escaped to space. some evidence for this scenario comes from the extremely high deuterium to hydrogen ratio in venus' atmosphere, roughly 150 times that of earth, since light hydrogen would escape from the atmosphere more readily than its heavier isotope, deuterium. venus is sufficiently strongly heated by the sun that water vapor can rise much higher in the atmosphere and be split into hydrogen and oxygen by ultraviolet light. the hydrogen can then escape from the atmosphere while the oxygen recombines or bonds to iron on planet's surface. the deficit of water on venus due to the runaway greenhouse effect is thought to explain why venus does not exhibit surface features consistent with plate tectonics, meaning it would be a stagnant lid planet. carbon dioxide, the dominant greenhouse gas in the current venusian atmosphere, owes its larger concentration to the weakness of carbon recycling as compared to earth, where the carbon dioxide emitted from volcanoes is efficiently subducted into the earth by plate tectonics on geologic time scales through the carbonate-silicate cycle, which requires precipitation to function.
runaway greenhouse effect
deforestation is a contributor to global warming, and is often cited as one of the major causes of the enhanced greenhouse effect. tropical deforestation is responsible for approximately 20% of world greenhouse gas emissions. according to the intergovernmental panel on climate change deforestation, mainly in tropical areas, could account for up to one-third of total anthropogenic carbon dioxide emissions. but recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation (excluding peatland emissions) contribute about 12% of total anthropogenic carbon dioxide emissions with a range from 6% to 17%. deforestation causes carbon dioxide to linger in the atmosphere. as carbon dioxide accrues, it produces a layer in the atmosphere that traps radiation from the sun. the radiation converts to heat which causes global warming, which is better known as the greenhouse effect. plants remove carbon in the form of carbon dioxide from the atmosphere during the process of photosynthesis, but release some carbon dioxide back into the atmosphere during normal respiration. only when actively growing can a tree or forest remove carbon, by storing it in plant tissues. both the decay and the burning of wood release much of this stored carbon back into the atmosphere. although an accumulation of wood is generally necessary for carbon sequestration, in some forests the network of symbiotic fungi that surround the trees' roots can store a significant amount of carbon, storing it underground even if the tree which supplied it dies and decays, or is harvested and burned. another way carbon can be sequestered by forests is for the wood to be harvested and turned into long-lived products, with new young trees replacing them. deforestation may also cause carbon stores held in soil to be released. forests can be either sinks or sources depending upon environmental circumstances. mature forests alternate between being net sinks and net sources of carbon dioxide (see carbon dioxide sink and carbon cycle).
deforestation