Lecture 31: Historical Climate: Volcanoes Lecture 31: Historical Climate: Volcanoes and Sunspotsand Sunspots

Ch. 16

• How do volcanoes affect climate?

• Name two important volcanic eruptions in the past one hundred years.

Historical Climate: Volcanoes and Sunspots

Ch. 16, p. 352-381; p. 381

• 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 MaximumClimate Change Since the Last Glacial Maximum

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

The Earth’s Climate History1. Over the last century, the earth’s surface temperature has increased by

about 0.75°C (about 1.35°F).

2. 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)

3. 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)

4. Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the current interglacial period)

5. Younger-Dryas Event = 12,000 ybp (sudden drop in temperature and portions of N.H. reverted back to glacial conditions)

6. 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)

7. 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.

8. For most of the earth’s history, the climate was much warmer than today.

Tropospheric & Stratospheric AerosolsTropospheric & Stratospheric Aerosols

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

Mt. Pinatubo Eruption & ImpactMt. Pinatubo Eruption & Impact

Recorded Recorded changes in air temperaturechanges in air temperature indicates the volcanic indicates the volcanic impact on climate.impact on climate.

Three months after the Three months after the June 1991 eruptionJune 1991 eruption of this Philippine of this Philippine volcano, much of the 20 million tons of volcano, much of the 20 million tons of ejected sulfur dioxideejected sulfur dioxide had had been directed by zonal stratospheric winds and been directed by zonal stratospheric winds and girdled the girdled the equatorequator..

Brief Episodes of Volcanic Cooling and El Nino WarmingBrief Episodes of Volcanic Cooling and El Nino Warming

Climate Change and Variations in Solar OutputClimate Change and Variations in Solar Output

MoreMore sunspots, sunspots,stronger solar stronger solar emissionsemissions from the from the Sun’s polar regions Sun’s polar regions and from the and from the bright bright marginsmargins of sunspots. of sunspots.

Sunspot History from TelescopesSunspot History from Telescopes

The telescope records The telescope records show:show:11-year sunspot cycle11-year sunspot cycle,,The Maunder The Maunder minimum.minimum.