ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuLecture 6: Climate Changes Lecture 6: Climate Changes  Tectonic-Scale Climate Changes Orbital-Scale Climate Changes Deglacial and Millennial Climate Changes Historical Climate Changes Global Warming(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuGlobal Surface TemperatureGlobal Surface TemperatureThe global average surface temperature has increased over the 20th century by about 0.6°C.19101945 1976 2000most of the warming happenedthe warmest year is 1998+0.17ºC/decade+0.14ºC/decadeWarmest years(1) 1998 – 0.63ºC(2) 2005 – 0.58ºC(3) 2002 – 0.56ºC2003(4) 2004 – 0.54ºC(5) 2001 – 0.51ºCESS200AESS200AProf. JinProf. Jin--Yi YuYi YuMore Warming in the N.H.More Warming in the N.H.Both the earlier period of warming (1910 to 1945) and the more recent one (1976 to 1999) saw rates of warming about twice as great in the Northern Hemisphere than in the Southern Hemisphere.ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuFaster Warming Trend Over LandsFaster Warming Trend Over LandsESS200AESS200AProf. JinProf. Jin--Yi YuYi YuClimate Change on Various Time ScalesClimate Change on Various Time Scales Tectonic-Scale Climate Changes Orbital-Scale Climate Changes Millennial Climate Changes Historical Climate Change  Anthropogenic Climate Changes(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuTectonicTectonic--Scale Climate ChangeScale Climate Change The faint young Sun paradox and its possible explanation. Why was Earth ice-free even at the poles 100 Myr ago (the Mesozoic Era)? What are the causes and climate effects of changes in sea level through time? What caused Earth’s climate to cool over the last 55 Myr(the Cenozoic Era)?Ice-free Earth(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuCirculation of the Solid EarthCirculation of the Solid EarthCold LithosphereFrom The Blue Planet The rising hot rocks and slid-away flows are thought to be the factor that cont5rol the positions of ocean basins and continents.Î The convection determines the shape of the Earth.ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuTwenty Rigid PlatesTwenty Rigid PlatesFrom The Blue PlanetESS200AESS200AProf. JinProf. Jin--Yi YuYi YuTectonic Control of COTectonic Control of CO22InputInput––The Seafloor The Seafloor Spreading Rate HypothesisSpreading Rate Hypothesis During active plate tectonic processes, carbon cycles constantly between Earth’s interior and its surface. The carbon moves from deep rock reservoirs to the surface mainly as CO2gas associated with volcanic activity along the margins of Earth’s tectonic plates. The centerpiece of the seafloor spreading hypothesis is the concept that changes in the rate of seafloor spreading over millions of years control the rate of delivery of CO2to the atmosphere from the large rock reservoir of carbon, with the resulting changes in atmospheric CO2concentrations controlling Earth’s climate.(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuWhy the Cooling over the Last 50 Why the Cooling over the Last 50 MyrMyr?? The collision of Indian and Asia happened around 40 Myr ago. The collision produced the Himalayas and a huge area of uplifted terrain called the Tibetan Plateau.  The Himalayas Mountains provided fresh, readily erodable surfaces on which chemical weathering could proceed rapidly. At the same time, the uplifting of the Tibetan Plateau create seasonal monsoon rainfalls, which provided the water needed for chemical weathering.  Therefore, the collision of India and Asia enhanced the chemical weathering process and brought down the atmospheric CO2 level to the relatively low values that prevail today. This reduced the greenhouse effect and cooled down the climate over the last 50 Myr.(from The Earth System)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuOrbitalOrbital--Scale Climate ChangeScale Climate Change Changes in solar heating driven by changes in Earth’s orbit are the major cause of cyclic climate changes over time scales of tens to hundreds of thousands of years (23k years, 41k years, and 100k years) .  Earth’s orbit and its cyclic variations: tilt variations, eccentricity variations, and precession of the orbit. How do orbital variations drive the strength of tropical monsoons? How do orbital variations control the size of northern hemisphere ice sheets? What controls orbital-scale fluctuations of atmospheric greenhouse gases? What is the origin of the 100,000-year climate cycle of the last 0.9 Myr (ice sheets melt rapidly every 100,000 years)?Why?(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuEarthEarth’’s Orbit and Its Variationss Orbit and Its Variations First, Earth spins around on its axis once every day Î The Tilt. Second, Earth revolves around the Sun once a year Î The shape of the Orbit. Both the tilt and the shape of the orbit have changed over time and produce three types of orbital variations: (1) obliquity variations(2) eccentricity variations(3) precession of the spin axis.(from The Earth System)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuHow Does the Tilt Affect Climate?How Does the Tilt Affect Climate? At present-day, the axis is tilted at an angle of 23.5°, referred to as Earth’s “obliquity”, or “tilt”. The Sun moves back and forth through the year between 23.5°N and 23.5°S. Earth’s 23.5° tilt also defines the 66.5° latitude of the Artic and Antarctic circles. No sunlight reaches latitudes higher than this in winter day. The tilt produces seasons!!(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuPrecessionPrecessionESS200AESS200AProf. JinProf. Jin--Yi YuYi YuMilankovitchMilankovitchTheoryTheory Milankovitch suggested that the critical factor for Northern Hemisphere continental glaciation was the amount of summertime insolation at high northern latitudes. Low summer insolation occurs during times when Earth’s orbital tilt is small. Low summer insolation also results from the fact that the northern hemisphere’s summer solstice occurs when Earth is farthest from the Sun and when the orbit is highly eccentric.(from Earth’s Climate: Past and Future)ESS200AESS200AProf. JinProf. Jin--Yi YuYi YuEvidence of Ice Sheet