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Natural Causes of Climate Change

Solar Variability Volcanoes Atmospheric Composition Earth Surface Properties Return Exam 3

For Next Class: Read Ch. 12 (pp. 371-373) & IPCC AR5 Ch. 2 (pp. 165-170)

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Spring 2016 Course Offerings

Introduction to Physical Geography Global Climate Change Global Change of the Biosphere World Regional Geography Intro to Human Geography Cartographic Design & Analysis Geospatial Data and Technology Communicating Geographic Information

Europe and the Russian Realm North Carolina Geography of the American South Weather and Climate Geography of Biodiversity Economic Geography Environmental Remote Sensing

Spring 2016 Course Offerings

Spain and North Africa Intro to Quantitative Methods Introduction to GIS Advanced GIS Principals of Geocomputation Geographical Hydrology Town, City and Regional Planning

Geospatial Data and Technology Planning Techniques Land Use Regulations Intro to Quantitative Methods Environmental Policy & Planning Community Development Senior Seminar

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Driving Question

What forcing mechanisms can bring about climate change and climate variability over a broad range of time and spatial scales?

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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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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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Global Radiative Equilibrium andClimate Change

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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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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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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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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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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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 SO2Mt. Pinatubo, June 1991

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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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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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Atmospheric Composition andClimate 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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Earth’s Surface Properties andClimate 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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Earth’s Surface Properties andClimate 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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Earth’s Surface Properties andClimate 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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Earth’s Surface Properties andClimate 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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Earth’s Surface Properties andClimate 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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Earth’s Surface Properties andClimate 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