Earth’s Climate & Mankind Long-term (years and longer) average condition of a region Rainfall or snowfall Snow and ice cover Temperature Weather Short-term (hours to weeks) fluctuations

Historical Examples of Climate Change? Advance and retreat of glaciers Alpine glaciers shrunk in 20th century Thinning of ice on NW Greenland See Nature v. 414, 60-62 Sea level rise El Nino/La Nina oscillations Length of growing season in Alaska increased from 1950-2000 Decrease in Arctic sea ice cover from 1970-2000

How We Will Study Climate Change

Time Scales of Climate Change

Earth’s Climate System Air, water, land and vegetation Changes in Earth’s climate system Driven by cause and effect Buzz words of climate scientists – forcing and response Forcing – factors that drive or cause changes Response – the climate change that occurs

Earth’s Climate System and the Interactions of its Components

Forcing & Response

Climate Forcing Tectonic Processes Slow movement of plates affects climate only very slowly

Climate Forcing Earth-Orbital Changes Variations in earth’s orbit around the Sun affect the amount of solar radiation received on Earth’s surface. Orbital scale changes occur over tens to hundreds of thousands of years.

Climate Forcing Changes in the Strength of the Sun Affects the amount of solar radiation received on Earth’s surface. Can occur on long-term (100’s of millions of years) or on short-term (10-1000’s years)

Climate Forcing Anthropogenic Forcing Not part of the natural climate system Affect of humans on climate Byproduct of agricultural, industrial and other human activities Example is addition materials to the atmosphere such as gases (CO2, N2O, etc.), sulfate particles and soot.

Response Time Time it takes the climate system to react to a change in forcing (reaction time) Response time = amount of time it takes to get 50% of the way toward equilibrium

Response Time Response curve exponential System moves ½ the way to equilibrium with each passage of response time Absolute amount of change decreases through time but proportional change towards equilibrium is constant

Time Scale of Forcing vs. Response Forcing is slow compared to response Climate system tracks forcing Typical of climate change on tectonic time scales

Time Scale of Forcing vs. Response Forcing is fast compared to response Little response to climate forcing Stochastic events with short-lived response

Time Scale of Forcing vs. Response Time scale of forcing = response time Yields dynamic and realistic response Frequency of forcing has a direct effect on the magnitude of the response The time scale of forcing is not long enough to allow the system to reach equilibrium

Cyclic Forcing and Response Natural climate forcing may vary in a cyclic fashion producing cyclic response Response time same; forcing is changing

Cyclic Forcing and Response Since forcing is constantly changing, equilibrium value of system also changes Equilibration values set by the rate and direction of change of the forcing Regardless of the forcing rate of change Response rate of the system is is fastest when the system is furthest from equilibrium

Cyclic Forcing and Response Frequency of forcing affects the amplitude of the response Slower cycling produces a larger response – more time to react Faster cycling produces a smaller response – less time to react

Cyclic Forcing and Response Cycling forcing and response typical of Milankovitch type orbital cycles Changes in incoming solar radiation due to changes in Earth’s orbit occur cyclically over tens of thousands of years Response time of large glacial ice sheets also tens of thousands of years

Response Rates & Interactions Different components of the climate system have different response times Different components will respond to a change in forcing at different rates

Response Rates & Interactions If climate forcing occurs in cycles, it will produce different cyclic responses in the climate system Fast responses track forcing Slow responses lag forcing

Response Rates & Interactions What happens to air temperature near the foot of the glacier if incoming solar radiation were to slowly increase?

Interactions in the Climate System Does the air warm due to increase in solar luminosity? Does the air stay cool because of the proximity to large mass of glacial ice? Response time of air influenced by both Response time of air will be faster than the response of the ice but lag behind forcing from the Sun

Interactions in the Climate System Individual components within the climate system do not respond passively to forcing Dynamic interaction between systems Interaction blurs the distinction between forcing and response Difficult to determine what system or systems are reacting to the forcing

Feedbacks in the Climate System Interactions can produce positive feedback Positive feedbacks produce additional climate change beyond that triggered by the initial forcing Positive feedback amplify changes

Feedbacks in the Climate System Interactions can produce negative feedback Negative feedbacks reduce the response that would be caused by the forcing Negative feedback suppress climate change