Lecture 31: Historical Climate: Volcanoes and Sunspots Ch. 16 This lecture was prepared on 1/23/2005 (Sunday). Took me 5 hours (from 8:00pm to 1:00am)

Historical Climate: Volcanoes and Sunspots Ch. 16, p. 352-381; p. 381 How do volcanoes affect climate? Name two important volcanic eruptions in the past one hundred years. How do sunspots affect climate? In what way do sunspot cycles before the 20th century imply a Sun-climate connections? Did volcanic eruptions and El Nino events affect the gradual trend of global temperature over the last century?

Climate Change Since the Last Glacial Maximum About 1000 y.a., the N.H. was cooler than now (e.g., 1961-1990 average). Certain regions were warmer than others.

The Earth’s Climate History Over the last century, the earth’s surface temperature has increased by about 0.75°C (about 1.35°F). Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output) Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland) Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the current interglacial period) Younger-Dryas Event = 12,000 ybp (sudden drop in temperature and portions of N.H. reverted back to glacial conditions) Last Glacial Maximum = 21,000 ybp (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America) We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ybp) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one. For most of the earth’s history, the climate was much warmer than today.

Tropospheric & Stratospheric Aerosols Auto emissions and wild land fires are 2 sources that emit aerosols into the troposphere that reduce incoming radiation and have a net cooling effect on earth's surface. Volcanic eruptions push aerosols into the stratosphere. Large eruptions, such as Mt. Pinatubo, have been linked to significant cooling episodes.

Mt. Pinatubo Eruption & Impact Three months after the June 1991 eruption of this Philippine volcano, much of the 20 million tons of ejected sulfur dioxide had been directed by zonal stratospheric winds and girdled the equator. Recorded changes in air temperature indicates the volcanic impact on climate.

Brief Episodes of Volcanic Cooling and El Nino Warming

Climate Change and Variations in Solar Output More sunspots, stronger solar emissions from the Sun’s polar regions and from the bright margins of sunspots.

Sunspot History from Telescopes The telescope records show: 11-year sunspot cycle, The Maunder minimum.