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Global Climate Change
The global alteration of Earth's climate system due to human activity resulting in globally increased temperatures
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Greenhouse Gases (GHGs)
- Gases in the atmosphere that absorb long-wave radiation reflected off Earth's surface and then re-radiate that heat back toward Earth
- Greenhouse effects occurs naturally
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Snowball Earth" without it
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What makes up greenhouse gases?
- CO2
- Methane
- Nitrous oxide
- Water vapor
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How do humans intensify greenhouse effect?
- Humans activities add CO2 and methane to the atmosphere from previously stable pools of carbon
- More GHGs in the atmosphere = more heat trapped = warmer Earth
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Carbon Cycle
Describes the movement of C through biotic and abiotic components of the Earth system
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Carbon pools
- Reservoirs of C that vary in residence tie and turnover rate
- Where carbon is stored such as trees and fossil fuels
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Carbon fluxes
Movement of C from one component of the cycle to another
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Turnover rate
- How quickly C moves from one pool to another
- Carbon pools have this and rates vary among pools
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Residence time
- How long C remains in a pool before moving to another
- Carbon pools have this and rates vary among pools
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Biospheric pool
- C stores in living tissue (mostly plants)
- Fast turnover and short residence time (respiration, death/decomposition)
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Fossil Fuels
- C stored in geologic deposits formed from organic matter
- Naturally: very slow turnover, long-residence times and previously didn't contribute to atmospheric C pool
- Humans: dramatically increased turnover form this pool to the atmospheric by burning fossil fuels (intensified greenhouse effect)
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How much CO2 is released by humans to atmosphere in 1 year?
- 17,640,000,000,000 lbs
- Fossil fuels burning = 80% of human CO2 emissions
- Other 20%, land-use change, primarily clearing forests
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Why is so much C stored in plants?
- Photosynthesis
- Carbon Fixation: process of converting inorganic C into organic C compounds in living tissues
- Wood is made up of cellulose and lignin, both C rich compound
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Carbon Sinks
Forests are reservoirs that accumulate C
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How does land-use change, like clearing forests for fuel or agriculture, contribute to atmospheric C pool?
- Eliminates photosynthesis and therefore less CO2 fixed from the atmosphere
- Burning wood releases additional CO2 to atmosphere
- Replace with livestock that are C sources (cow farts = methane)
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Why does the line wiggle up and down so much?
- Seasonal patterns in biospheric C uptake
- Trees grow in the summer and the leaves absorb carbon, CO2 decreases
- Trees loose leaves in the fall = less carbon absorption, so atmospheric CO2 increases
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Other than modern times, what was the highest CO2 level in the past 800,000 years?
A) ~300ppm
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How do we figure past CO2 levels?
- Layers of ice are laid down each ear
- Bubbles of air get trapped as ice freezes
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What is the modern CO2?
~400ppm
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The patterns of variation between CO2 and temperature
- CO2 and temperature strongly co-vary
- As CO2 increases, temperature increases
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Why does CO2 vary over time in absence of human activity?
The varying relationship between the Earth and Sun
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3 types of orbital cycles
- Obliquity: changes in how tilted Earth's axis is -> cycles last ~41,000 years
- Eccentricity: changes in how circular our orbit around the sun is -> cycles last ~100,000 years
- Precession: changes in the direction of Earth's tilt -> cycles last 19,000-23,000 years
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How is the solar cycle related to climate change?
- Large temperature changes caused by CO2 feedback loops initiated by changes in solar cycles
- Changes in precession, obliquity, and eccentricity alter amount of solar radiation received by the Earth
- But changes in solar radiation alone aren't enough to account for observed temperature variation
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How does solar radiation decrease due to solar cycles?
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Positive feedback loops
- Cycles that reinforce/strengthen the initial change as the cycle progresses
- Change in solar radiation initiates feedback loop, but change in CO2 due to feedback loop drives changes in climate
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What positive feedback loop would increase in solar radiation result in?
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What is linked to solar cycles that drove CO2 feedback loops?
- Long-term temperature changes
- CO2 feedback loops resulted in glacial and interglacial periods
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Would you predict that modern CO2 levels are driven by feedback loops initiated by solar cycle changes?
A) Yes
B) No
- No
- Current CO2 levels far above highest natural values for 800,000 years
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What does the plotted lines suggest about temperature increase?
A) The most recent time interval best fit lines have higher, more positive slopes indicating more rapid temperature increase
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Can modern warming be explained by solar activity?
- No
- Until ~1960, warming and solar irradiance followed similar pattern
- Post 1960 -> solar irradiance would predict cooling while temperatures increased due to increased GHG concentrations
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What will happen if we don't change our habits?
- Business as usual
- >8°F warming by end of century
- =4.5°C warming
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What would happen if there was immediate and rapid emissions reduction
2.5°F warming by ending of century
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Weather
- Short term variation in temperature and precipitation
- Varies hourly, daily, weekly, seasonally
- Weather systems=chaotic and unpredictable long-term
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Climate
- Long term average weather conditions
- Predictable based on known factors that drive climate patterns
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Climate change
Persistent changes in average weather conditions
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Why should we care about climate change?
- IN 2000: WHO estimated 150,000 people died annually from climate change
- The people who die the most don't even cause it
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What does WHO project in 2030-2050?
- Climate change will cause 250,000 additional deaths/years
- 38,000: heat exposure in elderly people
- 48,000: diarrhea
- 60,000: malaria
- 95,000: childhood malnutrition
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