Milankovitch Cycles – Flashcards

-1816 referred to as "the year without a summer" due to 1. snow in new england during summer 2. a dark, cold europe 3. crop failures across Europe and North America 4. Worst famine of 19th century -cause was the eruption of Mt. Tambora in Indonesia, the largest eruption in historical records that killed 70,000-100,000 people

-proposed that changes in the geometry of the Earth's orbit around the sun are responsible for the advance and retreat of continental ice sheets (glacial-interglacial intervals) -3 specific types of orbital variations 1. eccentricity 2. obliquity (tilt) 3. precession of the equinoxes

-earth's orbit around the sun -varies from near circle to ellipse with a period of 100,000 years -distance to sun changes and effects insolation (amount of solar radiation energy received over a given surface area, over a given amount of time) when earth farther from sun, insolation is lower

-tilt of the Earth's rotational axis -cycle of 41,000 years -varies from 22.2 to 24.5 degrees (current is 23.5) -if earth's orbit were circular: no tilt=no seasons 90 degree tilt=largest seasonal differences at the poles (6 months darkness, 6 months overhead sun)

-positions of solstices and equinoxes in the eccentric orbit, a slow change -period of 23,000 years

-tilt: controls intensity of seasons (warmer summer, colder winter) -precession and eccentricity: control length of seasons and small changes in total insolation -total changes in energy budget are small and the effect is a redistribution of energy

-longer, more intense summers lead to enhanced melting of ice sheet -colder winters don't grow more ice -a colder winter isn't enough to counteract a hotter summer that melts ice-- just because it is colder doesn't mean ice will grow

-earth based causes best account for long-term climactic change such as ice-house and green-house geologic periods -milankovitch cycles explain shorter term climate change (10-100 ka)

1270-1850 -not a true ice age, but there was a small drop in global temperatures, an ice sheet did not form -the cooling in Europe (1400-1900): colder winters and shorter growing seasons -evidence: 1. lakes, rivers, and ports in Europe froze 2. the european population seriously affected 3. mountain glaciers in the Alps of Switzerland and Austria advanced

-low solar activity (1645-1715): 50 sunspots over a 30 year period compared to normally 40,000 to 50,000 spots

-the solar constant is a measure of the total solar energy flux integrated across all wavelengths of radiation -two decades of satellite observations reveal that the solar constant varies over time scales of days to a decade, and there does appear to be a significant relationship with the sunspot number cycle

-oceans serve as one of the main mechanisms for redistributing heat

-"conveyor belt" transport heat from low to high latitudes at high latitudes- water cools and sinks- return flow at depth -driver: salinity, tropical waters are saline from evaporation, as they cool they get more dense, want to sink is an abrupt climate change evidence for a shutdown of the conveyor?

suggested that the time since the industrial revolution to be designated as a new geological period, the "anthropocene", because of the size and pervasiveness of human influence on Earth

-it is NOT just CO2, but it is the dominant contributor -water is also a greenhouse gas -again, greenhouse gases efficiently trap the sun's energy

-ice ages have waxed and waned over the last 800,000 years with linked changes in: 1. global climate (temperature) 2. volume of land ice 3. living world 4. sea level and area of coastal land 5. the concentrations of some gases in the atmosphere including carbon dioxide and methane

water vapor feedback: warmer atmosphere is wetter, water vapor is a greenhouse gas (+) cloud-radiation feedback: can reflect solar radiation (-), or absorb heat (+) ocean-circulation feedback: complex, warm sea surface, more water vapor, more active atmosphere, more wind, stronger ocean circulation ice-albedo feedback: as ice melts, less light reflected into space, more absorbed and so more ice melted (+)

-mathematical summaries of what we know about the mechanism of the climate system -one of the major tests of these models is to reproduce the main features of modern climate -another is to capture the dynamic changes of recent Ice Ages, in time and geographically any numerical model of climate is just a set of equations in a big computer

-the observed patterns cannot be explained without a major role for increased greenhouse gases especially carbon dioxide -increases in greenhouse gases overwhelmingly result from human activities -human activities CAN and HAVE changed global climate

Intergovernmental Panel on Climate Change -put together info on climate and climate science -can compare a variety of models and get a main message from the results -point is to show why climate scientists believe that humans have effected the climate mostly through our emission of greenhouse gases -- the effects are real and can be measured over time

-there have been large, unprecedented, increases in carbon dioxide and other human-produced greenhouse gases over last 150 years -temperature has increased at a rate, in places and at times distant and recent, consistent with model projections including major greenhouse gas effects -major physics of the greenhouse effect support this

-the common pattern of variability seen in many kinds of record, and many analyses for the last several centuries shows the late 20th/early 21st century as the warmest period for several hundred years -until the 20th century the general pattern can be accounted for by solar and volcanic forcing -it is not possible to reasonably explain the course of change from the 19th to late 20th century without greenhouse gases and sulfate aerosols