7 - Climate Change
Obliquity
Obliquity is the angle of the Earth's axis relative to the plane of its orbit. Variation in Axial Obliquity (i.e., tilt) changes the contrast between the seasons. 0º axial tilt would mean that the axis is perfectly perpendicular to the plane of orbit around the sun. The earth's axial tilt varies between 22.1º and 24.5º on a cycle that averages around a 41,000 year period. -all the planets are spinning around the sun in close to the same plane, but their axes are not perfectly perpendicular (90 degree angle) to that plane. The earth's axis is tilted from 22.1 and 24.5 degrees off of perfectly straight up and down. -this tilt in axis creates the seasons, and the difference in seasons between the north and south. During part of the orbit the Northern hemisphere will be angled towards the sun. During the opposite half of the orbit the Southern hemisphere will be angled towards the sun.
Orbital Forcing and Milankovitch Theory
Orbital features of the Earth as it orbits the Sun influence the Earth's climate. This is orbital forcing. Explained by the Milankovitch Theory of orbital forcing. Helps to explain why the poles are more effected than around the equator Three features of the Earth's orbit around the Sun greatly influences Earth climate: 1)Orbital Eccentricity 2)Obliquity 3)Precession *These three factors each operate on timed cycles of when they make the Earth hotter and colder. The Earth's Milankovitch cycle is a combination of the three cycles.
Ocean Currents
Oscillations in ocean surface temperatures can also influence climate. -NASA took a picture that showed the temperature of the Earth over the whole globe on two days, four years apart. -El nino is basically a very warm stretch of water that goes out from Equador into the Pacific. -La nina is the same body of water going out from Equador, but getting very very cold. -They cycle on a four or five year basis. This has HUGE effects on weather around the world (wind, rainfall, temp., etc.).
Albedo effect on glaciers
-Melting polar glaciers can set up a positive feedback to accelerate global warming. As more of Greenland's polar ice sheet melts, there is more non-white area to absorb light and warm up the landmass, which aids in further melting. So the albedo effect means that it is very hard to heat an area covered in ice, but once heating gets started, it is accelerated.
A possible result of the albedo effect: snowball Earth
-a period known as snowball Earth, when the entire Earth, or almost all of it, is covered in white, and so is very very very hard to reheat. It happened twice, once about 700 million years ago, and once about 650 million years ago. At these two times, the entire Earth was encased in glacier. Keep in mind, life began 3.4 billion years ago. So life on earth has lived through two period of TOTAl freeze across entire globe, complete glaciation of the Earth. How did life survive? Some theorize that life existed only around tiny cracks in the ice where some light could get through and allow photosynthesis to happen and so allow energy to keep entering the food chain of life. -geologists wonder about this theory, because how did the Earth manage to get out of this? Albedo effect would make it really hard. there are many theories.
Total Solar Radiation influences global temperature
-blue line on graph is temperature record since invention of thermometer; red line on graph is amount of energy put out by the sun. We have this data since 1880, b/c that is when the instruments are invented. -for most of the graph, the red and blue lines correlate very well, with the sun like a furnace heating the Earth. We think the sun's energy output is what caused the warm period in Medieval times and the cold period (Little Ice Age) in Rennaisance times. -however, after around 1970, energy received by Earth from the sun drops off but temperature spikes. So something very different is happening after around 1970 than what was happening before.
National Research Council Summary of Climate data provides a graph of global temperature for the last 1,000 years.
-during the medieval period (1000 AD to 1450 AD) temperature went way up -during the Renaissance period (1450 AD to 1800 AD) it got very cold again. -during the medieval period, the Vikings were going all around the world, because there wasn't ice blocking their ships and it was warm and easy enough to colonize places. They set up a colony on Greenland that lasted for 200 years (at the warmest period of the last 1,000 years). Then they all starved to death because plants stopped growing, because it got too cold by 1350. By 1700 it was pretty warm again but not was warm as it had been before the start of the little ice age. Based on temperatures measured by instruments, the Earth warmed ~0.6ºC in the 20th century. Many different data sources, not just ice cores, support this conclusion. *After 1880 we have records from thermometers. Temperature increased in 1970-2000 more than any time in the past 400 years.
Global Temperatures in the last 450,000 years (extracted from Vostok ice cores)
-in recent history of earth, there seems to be a temperature spike every 100,000 years. This aligns with the cycle of orbital eccentricity. The pattern of temperature on the earth has been very closely determined by orbital eccentricity cycle for the last 5 million years. -the places between the spikes in temp are the glacial periods (periods when there are glaciers sitting on both of the poles). At the spikes, the glaciers melted and then rapidly reformed.
What are the consequences of recent, rapid climate changes?
-scientists are searching for contemporary evidence of the biotic effects of climate change. Over the last 40 years, is there any change in species due to response to climate change? Yes, there is a really significant amount of change, AND the change is in the direction predicted by the scientists to be the direction of change if climate change is really happening and is affecting species. What might some possible changes be? Scientists predicted changes like changes in migration due to temperature changes, plants might flower at different times, mating happening at different times. All these predicted changes are indeed happening. -will change rates of precipitation: the poles will get far more precipitation and around the equator will get drier and drier. -as glaciers melt, ocean level will rise and cover coastal areas. salinity of ocean will also go down, affecting marine life. -arable agricultural areas will be affected, decreasing food supply. areas suitable for different crops (wheat, rice, corn, soybeans, fish, grapes, etc.) will change, so industries will have to move to new countries.
Testing Ice cores to discern temperature of climate at time when the ice froze.
-to get temperature data out of ice cores from glaciers, you look at the isotopes of gases in the ice. In ice this is mostly done with oxygen isotopes, the amounts of which correlate pretty well with average global temperature. the isotope method is also used to study tree rings and corals (it is true that tree rings are bigger if the tree grew more one year, but that doesn't tell you what conditions caused the greater growth so this method is not very helpful in climate study). Because enzymes pick up different isotopes at various rates at different temperatures, you can tell what the temperature was at the time the ice or tree ring was created.
Albedo Effect
Albedo is the percentage of incident radiation that is reflected. The color black absorbs lots of light, the color white reflects it. Reflected radiation is not absorbed, and so is not heating. So black things (and anything other than pure white) heat up faster than white things. -when snow melts: if even a little bit of ground is exposed (or something other than the color white), that will heat up much faster relative to the snow around it, and will be able to melt the snow at the edges of that patch of ground. The more non-white is exposed, the faster the snow around it will melt. So melting of snow accelerates quickly, snow doesn't melt at the same rate from start to finish. -cities tend to be a few degress warmer than the surrounding countryside because all the black pavement absorbs heat and radiates it at night.
Effect of changes in global temperature on life forms: speciation and extinction
Change in global temperature can have major effects on speciation and extinction. Species come and go in correlation with changes in environment, as well as other factors. The history of climate change and cycles of growth and retreat of glaciers has been a part of the diversification of every clade (branch of the tree of life) that exists today.
Kepler's Three Laws of Planetary Motion
Kepler's Laws of Planetary Motion: 1)The orbit of every planet is an ellipse with the Sun at one focus. 2)A line joining a planet and the Sun sweeps out equal areas during equal intervals of time. 3)The square of the orbital period is directly proportional to the cube of the semi-major axis of its orbit.
Major drivers of the Earth's climate
Major drivers of the Earth's climate: 1)Sun Strength and Intensity (-the strength of sun rays fluctuate throughout the day and year) 2)Orbital forcing (the way the Earth goes around the sun, as determined by Milankovitch cycle) 3)Oceanic currents (El Niño and La Niña) 4)Major Volcanic activity 5)Albedo 6)Changes in atmospheric gas concentrations (C02 and other gases)
Global Temperature record for the last 65 million years
Record of ocean silt goes back 2 or 3 hundred million years. -65 million years ago, the earth's average temperature was about 7 degrees centigrade warmer than it is today (about 13 degrees farenheit) -the globe was much much warmer back then. 65 mya was about the time the dinosaurs died out. -some of the best dinosaur fossil hunting is at the poles, because dinosaurs roamed all the way up there and down there (giant lizards are cold-blooded, don't do well in cold, so poles must have been warm back then) -about 34 mya ago the Earth cooled down greatly (this is when glaciers formed on the poles). -the global temp has been fluctuating at an increasing rate in the last 5 million years. back in the day it was relatively steady, experiencing long term trends over time, but not jumping rapidly up and down. Now, in the Pleistocene period (means time of glaciers), it jumps up and down at an increasing rate. for the last 4 or 5 million years, the climate has been girating, jumping up and down up and down. But still, overall, way cooler than 65 mya
Volcanoes can effect global temperature.
The gasses spewed from volcanoes can have substantial effects on the global climate. -when all the ash goes into the upper atmosphere and spreads around the globe, it reflects sunlight and blocks energy from getting to the surface of the earth, and so the global temperature goes down. You can clearly see the effects in rates of solar radiation reaching the Earth, and in global temperature.
Data from 1888 to 2012 shows that the poles, particularly the Northern pole, experiences the most drastic increase in temperature.
The poles are undergoing more dramatic temperature increase than the rest of the world. The biggest effects of global warming have been at the poles, and will be in the future. Why might that be?
Ancient C02 concentrations over the Earth's history correlate with the Earth's Milankovitch cycle.
The recent climate record shows a ~100,000 year cycle (result of Orbital Eccentricity?). There is strong correlation with CO2 and CH4 concentrations, and global temperature. C02 concentrations seem to go up and down as global temperature goes up and down. This is data from Vostok ice cores. Vostok is a place in Antarctica where the longest ice cores have been extracted. They date back to 450,000 years.
North America was a very different place 20,000 years ago than it is today
Two images of North America, one from 18,000 years ago and one from today, showing what biomes exist where on the continent. The old one is reconstructed by pollen and leaf fossils. It shows a massive change in biomes, with most of N. America being covered in glacier 18,000 years ago and today being a mix of many warmer biomes with ice and tundra only in the very far north. -there were GIANT animals back in the day. It was much more like today's African Savannah. they all went extinct around 18,000 years ago -18,000 years ago there was a kilometer of ice over Hanover. -The ocean was much shallower than it is now, because so much water was taken up in ice. -18,000 years ago the average global temp. was around 8 degrees C colder than it is today.
Precession
Variation in Orbital Precession (i.e., orbital wobble) changes the contrast between the seasons in the different hemispheres on a period of ~26,000 years. The wobble is the wobble of the earth's axis. Not only does the angle of the earths axis in relation to the plane of orbit change on a 41,000 year period (obliquity), but the axis also wobbles in a circle on a 26,000 year period (precession). This also effects global temp and temp of different hemispheres in different seasons.
Orbital Eccentricity
orbital eccentricity= how much the Earth's orbital varies from a perfect circle. *Kepler's first law defines orbital eccentricity. The greater the distance between the foci of the ellipse, the more eccentric the orbit. So for example, if the two foci are coincident (on top of each other), the orbit would be a circle. Because the planet moves faster as it gets closer to the sun and slower while it is far away from the sun, the planet cools during the majority of its travel. If the distance between the foci is larger, the orbit will take longer and relatively more of it will be spent cooling than warming. The eccentricity of the Earth's orbit varies on a cycle of 100,000 years. The second law means that where the planet is in its orbit (how close or far from the sun) effects how fast the planet is moving. the Earth moves slower when it is farther from the sun and faster when it is closer. this, combined with the effects of the first law, determines how much time the Earth spends near the sun being heated, and how much time it spends far from the sun cooling off. If the orbit is more circular, not only is the planet on average closer to the sun throughout the orbit, but since its distance from the sun (and therefore both its speed and how much heat it is receiving at a given time) doesn't vary as greatly as it would in a highly elliptical orbit. Fluctuations in the distance between the two foci lead to changes in temperature: when they are farther apart, the Earth has a more elliptical orbit and so spends more time farther from the sun (and is moving slower at this time) than it would if they were closer together and the orbit more circular.
phylogeography
phylogeography: looking at a population's genome to tell where a population came from and how it spread as the glaciers melted. it shows us that rapid climate change causes species to rapidly shift their ranges.
