1. Natural Causes of Climate Change
Current News and Weather
Solar Variability
Volcanoes
Atmospheric Composition
Earth Surface Properties
For Next Class: Read Climate Studies Chapter 12
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5. Driving Question
What forcing mechanisms can bring about climate change and climate variability over a broad range of temporal and spatial scales?
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6. The complex spectrum of climate variability and climate change is a response to the interactions of many forcing agents and mechanisms operating both internally and externally relative to the Earth-atmosphere-land-ocean system
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7. Natural Forcings
What are some examples of natural forcings on climate and their temporal and spatial scales?
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8. One way to organize our thinking on the many possible causes of climate change is to match a possible cause with a specific climate fluctuation based on similar periods
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9. Global Radiative Equilibrium
Any change in either energy input or energy output will shift the Earth-atmosphere-land-ocean system to a new equilibrium and change the planet’s climate
Factors that can alter the global radiative equilibrium
Fluctuations in solar energy output
Changes in Earth’s orbit about the Sun
Volcanic eruptions
Variations in atmospheric chemistry
Alterations in Earth’s surface properties
Certain human activities
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10. Solar Variability and Climate Change
Sun’s total energy output at all wavelengths is not constant
Numerical global climate models predict
that only a 1%
change in the Sun’s
energy output could
significantly alter
the mean
temperature of the
Earth-atmosphere-
land-ocean system
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11. Solar Variability and Climate Change
Sunspots
Changes in solar energy output apparently are related to sunspot number
More sunspots may contribute to a warmer global climate and fewer sunspots may translate into a colder global climate
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12. Solar Variability and Climate Change
Sunspots
Typically lasts only a few days
Number of sunspots varies systematically with time between successive sunspot maxima or minima
averaging about 11 years
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13. Solar Variability and Climate Change
Maunder Minimum and the Little Ice Age
Sunspot activity greatly diminished during the 70-year period from 1645 to 1715 and coincided with a cold episode in Europe
The magnitude of the variation in solar energy output during an 11-year solar cycle is so little that some amplification mechanism is required for sunspots to influence climate
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14. Volcanoes and Climate Change
In violent eruptions, volcanoes discharge ash particles and sulfur dioxide into the stratosphere, creating a veil that can cause cooling at Earth’s surface
Must be a violent eruption, at low latitudes and rich in SO2
Mt. Pinatubo, June 1991
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15. Volcanoes and Climate Change
By influencing the flux of radiation and attendant changes in global circulation patterns, the Pinatubo eruption was likely responsible for the cool summer of 1992 over continental areas of the Northern Hemisphere
Temperature anomalies in the Midwest during June, July, and August 1992.
(Following Mt. Pinatubo eruption)
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16. Volcanoes and Climate Change
An eruption is unlikely to lower the mean hemispheric or global surface temperature by more than about 1.0 Celsius degree (for a year or two) although the magnitude of local and regional temperature change may be greater
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17. Atmospheric Composition and Climate Change
Natural processes have played important roles in regulating levels of greenhouse gases and global climate
Extinctions of plants and animals have been linked to increases in atmospheric CO2 levels associated with massive volcanic eruptions
Methane was an important contributor to post-glacial warming at high latitudes
Release from methane hydrates on the seafloor
Emission from northern wetlands as temperatures rose
Thermokarst lakes
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18. Earth’s Surface Properties and Climate Change
Snow and Ice Cover
Changes in mean regional snow cover may contribute to climate variability and climate change.
Fresh-fallen snow
typically reflects 80% or
more of incident solar
radiation, reducing the
amount of solar heating and lowering the daily maximum air temperature.
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19. Earth’s Surface Properties and Climate Change
Snow and Ice Cover
Whereas changes in regional snow cover might impact climate variability over the short-term, changes in Earth’s sea ice or glacial ice coverage are likely to have longer-lasting effects on climate
Ice reflects much more incident solar radiation than either the ocean or snow-free land
Any change in glacial or sea ice cover would affect climate
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20. Earth’s Surface Properties and Climate Change
Shrinkage of Arctic Sea-Ice Cover
Melting of floating sea ice does not raise sea level, but it can alter climate significantly
Shrinkage of Arctic sea ice is likely to trigger an ice-albedo feedback mechanism that would accelerate melting of sea ice and amplify warming
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21. Earth’s Surface Properties and Climate Change
Shrinkage of Arctic Sea-Ice Cover
Arctic sea ice cover varies seasonally and exhibits some long term trends
In recent
years there
has been a
decline in
the winter
maximum
extent of ice
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22. Earth’s Surface Properties and Climate Change
Shrinkage of Arctic
Sea-Ice Cover
After 2000, the rate of
reduction of Arctic sea
ice cover accelerated
The end-of-summer ice extent reached a record low in 2007
If current trends continue, by 2037 the Arctic Ocean may be free of sea ice in the summer
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23. Earth’s Surface Properties and Climate Change
Sea-Surface Temperature Pattern
Changes in ocean circulation and sea-surface temperatures contribute to large-scale climate change and climate variability
Some climate shifts can be abrupt, occurring in a decade or less
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