Lecture 5 - volcanoes and climate

Question 1

explain mount Tambora 1815 eruption - that caused the year without a summer

Answer 1

• Largest eruption of past 10,000 years (Volcanic Explosivity index 7)
• 100 km3 of ash, pumice and aerosols
• 60 Megatons of sulfur
• Ash plume reached 43 km altitude
• Tsunamis (4m high) due to pyroclastic flows entering the sea

Question 2

What were the impacts of mount Tambora 1815

Answer 2

• 10,000 direct deaths (by pyroclastic flows and ash fall)
• 82,000 indirect deaths by starvation and diseases
• Orange to red sunsets
• Persistent “dry fog” in NE USA -> stratospheric sulfate aerosol veil
• Persistent rain in western Europe
• Severe frost in NE USA in June, July 1816
• 1 - 3°C cooler summer temperatures in W and central Europe
• Food shortages and highly increased food prices in Northern America and Europe.
• inspired literature of the time.

Question 3

what chemical processes occur in the atmosphere?

Answer 3

The atmospheric effects cause net cooling
Co-injection of water with SO2 results in enhanced rate of sulphate formation.
* H2O increases availability of OH- radicals, which rapidly convert SO2 to sulfate aerosols,
including an increased rate of aerosol growth.
 Aerosols reflect shortwave radiation from space -> cooling
 Aerosols scatter longwave radiation from Earth -> warming

Question 4

How does the hydrological cycle react to a volcanic eruption.

Answer 4

large volcanic eruptions = decrease of precipitation, particularly in wet regions (tropics).
- stratospheric aerosols reflect sunlight, reducing evaporation.
- cooler temperatures stabilize the atmosphere and reduces water-holding capacity (drying).
- reduced stream flow for major tropical river systems
- increased stream flow in SE USA, parts of Europe.

Question 5

Effects of large explosive tropical and high latitude volcanoes on weather and climate in tropical eruptions

Answer 5

• enhance or reduce El Nino
• reduction of diurnal cycle
• summer cooling of NH tropics, subtropics
• reduced tropical precipitation
• reduced Sahel precipitation
• ozone depletion, enhanced UV
• global cooling
• stratospheric warming
• winter warming of NH continents.

Question 6

enhance or reduce El Nino (what’s the mechanism, beginning time and duration)

Answer 6

Tropospheric absorption of shortwave and longwave radiation
begins after 1-2 weeks
lasts for 1-2 years

Question 7

Reduction of diurnal cycle

Answer 7

Blockage of shortwave and emissions of longwave radiation
begins immediately
lasts for 1-4 days

Question 8

Summer cooling of NH tropics, subtropics

Answer 8

blockage of shortwave radiation
begins immediately
lasts for 1-2 years