2 Overview Similarities to Earth Differences from Earth Current situations of both planets (recap)The “dry” runaway greenhouse effectThe “wet” runaway greenhouse effectHow they relate to EarthSkeptics of either/or scenarios on EarthAn example of it already happening
3 Similarities Orbital radius is 70% that of Earth’s. Planetary radius is 95% of Earth’s.One of the inner “rocky planets”Has similar mass and density.Surface features of highlands and lowlands.Abundant atmosphere.Geological processes still continue (volcanoes, etc)
5 Differences Makes one axial rotation every 243 Earth days. Orbits in retrograde motion.Tilted degrees compared to Earth’s 23.5 degrees.Atmosphere 90 times more massive than Earth’s.Very high atmospheric concentration of CO2Has very low amounts of hydrogen.
6 Current Situations Venus: Barren wasteland Avg. Temp of 900° F 96.5% of atmosphere is CO2No waterClouds of sulfuric acidBehaves as it was expected toEarth:Supports lifeAvg. Temp of 57 ° F0.04% of atmosphere is CO2Abundant waterClouds of water vaporDeviates from expected behavior
7 Why is this so?Venus and Earth both formed approximately 4.5 billion years ago and given their similarities, should have turned out the same, but they do not. Why didn’t they?How is it that Earth can support life when Venus is completely hostile to it?The answer: Global warming.
8 Two Runaway Greenhouse Effects “Dry” Runaway Greenhouse Effect – no liquid water.“Wet” Runaway Greenhouse Effect – liquid water present.
9 “Dry” EffectVenus was closer to the sun and this proximity didn’t allow water to condense.Since no water condensed, carbon dioxide could not be taken out of the atmosphere by oceans.Outgasing from the planet (through volcanoes) would continue to increase amounts of CO2 and water vapor in the atmosphere.This heating leads to whatever water vapor present to rise to the top o the atmosphere.It is broken in oxygen and hydrogen molecules by ultraviolet light.Lighter hydrogen escapes into space, oxygen left recombines with other elements like sulfur and oxygen.The planet loses hydrogen, and in effect loses all the water it had and becomes the inferno that it is today.
10 “Wet” Effect The water on Venus did condense into oceans. Higher temperatures than Earth would cause it to evaporate large amounts of water into the atmosphere.It would not precipitate back since the temp. was so high and oceans gradually vanished.The higher temperature also caused rocks to hold carbon less effectively and carbonates would eventually undergo processes releasing their stored carbon.As more water vapor enters atmosphere, the temperature rises even more and when the oceans were completely gone, water vapor again starts to rise to the top of the atmosphereThey are then broken up by ultraviolet rays and hydrogen escapes into space while oxygen remains and recombines.The planet STILL loses all its water even if it once had liquid oceans.
11 Earth’s Greenhouse Effect Greenhouse gases on Earth, carbon dioxide, methane, ozone, and water vapor raise the temperature of the planet.Without the greenhouse effect, the planet would be -13° F, with it, it is about 55 ° F.Most of the greenhouse effect comes from carbon dioxide which is responsible for 57% of the total.
12 Venus Relevance to Earth Human activity is increasing greenhouse gas concentrations.Every year 6 billion tons of carbon dioxide alone are put into the atmosphere.In the past 133 years, avg. global temp. has risen by 0.5° C or 1 ° F.By 2100 it is expected to rise anywhere from 1.5 ° C to 5.5 ° C (2.7 ° F to 10 ° F)This may or may not be enough to trigger a “Wet” Runaway Greenhouse Effect
13 Venus Relevance to Earth (cont.) A “Wet” Runaway Greenhouse Effect on Earth would require that the majority of the oceans around the world evaporate more water than they get back through precipitation.The average temperature where this is occurs is more than 80° F.Currently, the highest ocean surface temp. at any given time usually does not rise above 87° F.The average ocean surface temp. varies between 50° to 60° F (closer to the 50).If by 2100 the average global temp. rises by 10° F then the average surface temperature could possibly rise to about 70° F, this is much closer to the doomsday number of just slightly over 80° F.If this process were ever to start, it would be impossible to stop given the vast energies involved in it.
14 Venus Relevance to Earth (cont.) All the water would evaporate into the atmosphere, fueling more global warming until all the oceans were gone.At this point, water molecules in the atmosphere would move closer to the top of the atmosphere and get broken apart by ultraviolet rays.The reason ultraviolet rays would affect them more at that point than now is because there would be virtually no ozone layer left at this point.Global warming contributes to the destruction of ozone.Once the water molecules were broken up, hydrogen would escape into space, just like on Venus and oxygen would remain to recombine with other elements.If this sounds similar to Venus, it should. Venus, in becoming the 900° F inferno that it is, follows and expected path of progression while Earth is the anomaly, not the other way round.The only things preventing Earth from fulfilling its expected outcome are the carbon cycle, since oceans remove a great deal of carbon dioxide and keep it in check and life, since many organisms (such as shellfish) create carbonates in the form of shells and help take carbon dioxide out of the atmosphere.This is a very delicate process that can be easily upset.
15 Skeptics’ ArgumentsSkeptics of either scenario happening have some facts to try and support their claims.One compelling argument they make is that carbon dioxide is only 0.04% of the Earth’s atmosphere and, to date, humans have contributed only 3% directly.Although 6 billion tons of CO2 may be released every year into the atmosphere by humans, 200 billion is released by natural processes in the same time frame.But their one flaw is that they fail to realize how fragile the system is and how narrowly Earth avoided becoming a second Venus.A disruption of the carbon cycle that keeps global temperatures in check could change…
19 Example Already Happening In fact, a very localized scenario of the “wet” runaway effect has already occurred.In May of 2002, scientists discovered an area in the Pacific Ocean to the North East of Australia that exhibited a runaway effect.This location was warm enough year round to continually evaporate more water vapor than precipitated back to it.Luckily, since it is only a localized area, surrounding parts of the ocean compensate for it. If the entire planet were to runaway, however, there would be no other areas to compensate.This one example shows that we could very well be close to the entire planet running away.
20 ConclusionAction must be taken now to avoid the Venus outcome happening on Earth.If it is indeed the one planet that supports life, human beings have a great responsibility to preserve it.Hope everyone has a good winter break!