Lecture 17 Tectonic-scale Climate Change

Greenhouse/Icehouse Earth (Part II, p. 84-85; Ch. 4, p. 86-91) Geologic Time Scale No ice sheets on land Ice sheets on land * * * * * * Ice House

Tectonic-scale Climate Change (Ch. 5, p. 103-112) Hundreds of millions of years Plate tectonics and drift concentrated continents at higher latitudes allowed for more ice cover, which reflected more sunlight and created a positive feedback to cause greater cooling.

Tectonic-scale Carbon Dioxide Fluctuations (p. 91-99; p. 103-121) Seafloor spreading leads to increased periods of volcanic degassing of CO2, which causes warming. Higher temperatures leads to increased weathering, which will remove CO2 from the atmosphere and reverse warming in a negative feedback loop.

Earth’s Climate History in the Last 550 Myr Over the past 550 Myr, three Icehouse periods (430, 325-240, 35-0 Myr ago). 2. For most of the last 550 Myr or the earth’s entire history, the climate was much warmer than today. 3. Tectonic-scale climate change is caused by plate tectonics Bradley Fig.1.1 Churchill quote "The farther backward you can look, the farther forward you are likely to see." - Winston Churchill Land/ocean positions and sizes Ocean floor spreading/CO2 increase Mountain building (uplift) & weathering / CO2 decrease 4. Other causes. Part II p. 82-83; Ch. 4, 5, 6, 7

Chemical weathering (chemical breakdown of minerals or rocks) Carbonic acid Examples: (Calcite) (calcium ions) Limestone + carbon dioxide + water  dissolved ions + bicarbonate CaCO3 + CO2 + H2O  Ca2+ + 2HCO3-

The World 100 Myr Ago (p. 129-137) Flooding of The Continents

Cretaceous  Greenhouse Earth Warm period of dinosaurs Evidence No record of glaciers or polar ice caps Faunal/floral zone latitudinal shift Isotopes  warmer oceans Environments shift with near tropics to the poles Oceans/Atmosphere/Land Features Sea level 100-200 m higher because of no polar ice caps Intense storms (hurricanes) because of warmer waters Stronger hydrologic cycle Less wind because lower T and P gradients globally More plants, more flowers; extent of dry land reduced by flooding Causes Sun-Earth relationship Land-sea configuration More oceans in low latitudeslower albedo More land in high latitudesmore plants More CO2 in atmosphere (4-8 x) Bradley Fig.1.1 Churchill quote "The farther backward you can look, the farther forward you are likely to see." - Winston Churchill

1. The last time atmospheric CO2 concentrations and temperatures were much higher than today was in the age of dinosaurs. 2. Agriculture revolution began 10,000 years ago. 3. Human population explosion in the past 100 years. Today: 6 billion 18,000 years 230,000 years 1 Million years 3.5 Million years 10 million years 6 5 million years 10,000 years 1,000 years 55 million years Today’s climate is becoming extreme The climate that humans are creating is unusual. The earth hasn’t experienced an extended period of temperatures as warm as today’s for a very long time - many millions of years. The last time atmospheric CO2 concentrations and temperatures were much higher than today was in the age of dinosaurs. The world looked very different then. Most of the earth was more like what we now associate with very tropical area. High humidity, warm temperatures, lots of rain, little or no frost. Although the Earth and some of its living organisms have experienced climates more extreme than todays, most modern plants and animals have evolved in mild or cold climates, as the Earth has experienced in the past million years or so. The climate of today is right at the hottest peak that many modern living species have “experienced” (in an evolutionary sense). Human civilization has blossomed in the last 10,000 years, during a time of great climate stability. PRESENT 100,000 years

The only mammals living at this time were small rodents. When dinosaur’s ruled the Earth, the only mammals that existed were small, rodent-like things. Large mammals, like horses, elephants, and lions, did not evolve until much later. By the time these larger mammals were evolving (including early hominids), Earth’s atmosphere was lower in CO2, and the climate had begun to cool and become drier. (Photo Copyrighted by Nelson Guda, 2000.)

What about Texas? Sea levels were much higher than today, and Texas was mostly under water When the dinosaurs ruled the world, Texas was mostly under the sea. No one is expecting this to happen again, but rising sea levels are one of the biggest concerns if global warming continues. Texas is particularly vulnerable because of its long coastline which contains many of its major cities and recreational areas (Houston, Galveston, Padre Island National Seashore). Further, a large part of the population of the state lives in low-lying areas and is vulnerable to flooding during storms at sea (hurricanes). Sea levels were much higher than today, and Texas was mostly under water

Climate change was one important reason that the dinosaurs disappeared. Climate change was one of the main reasons for the disappearance of the dinosaurs. The world became dryer and cooler, and one by one, the different species of dinosaur went extinct. Scientists believe that this climate change had multiple causes. The two main causes of climate change are thought to be: Gradual drifting of the continents away from the tropics and towards the poles. This occurred over millions of years. A sudden cooling may have been brought on by a very large meteor hitting the earth, spewing tons of ash into the air, blocking out the sunlight, and preventing heat from reaching the ground. This 'global cooling' effect was long-lasting. The earth has had very few times since then that match the extreme tropical climate in which the dinosaurs flourished. Mosasaurus maximus (Photo credit by Texas Memorial Museum) Climate change was one important reason that the dinosaurs disappeared.

Global Cooling Trend in the Last 55 Myr Ch. 7 Causes: decrease in ocean floor spreading rate; uplift weathering; ocean heat transport through gateways; ice-albedo feedbacks Cooling from leaf outline Cooling from ocean isotopes Decrease in spreading rate Bradley Fig.1.1 Churchill quote "The farther backward you can look, the farther forward you are likely to see." - Winston Churchill