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 © AMS

© AMS

© AMS

© AMS

Driving Question What forcing mechanisms can bring about climate change and climate variability over a broad range of temporal and spatial scales? © AMS

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 © AMS

Natural Forcings What are some examples of natural forcings on climate and their temporal and spatial scales? © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS

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) © AMS

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 © AMS

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 © AMS

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. © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS

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 © AMS