Global Climate Change
The global alteration of Earth's climate system due to human activity resulting in globally increased temperatures
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
- "Snowball Earth" without it
What makes up greenhouse gases?
- Nitrous oxide
- Water vapor
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
Describes the movement of C through biotic and abiotic components of the Earth system
- Reservoirs of C that vary in residence tie and turnover rate
- Where carbon is stored such as trees and fossil fuels
Movement of C from one component of the cycle to another
- How quickly C moves from one pool to another
- Carbon pools have this and rates vary among pools
- How long C remains in a pool before moving to another
- Carbon pools have this and rates vary among pools
- C stores in living tissue (mostly plants)
- Fast turnover and short residence time (respiration, death/decomposition)
- 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)
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
Why is so much C stored in plants?
- 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
Forests are reservoirs that accumulate C
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)
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
Other than modern times, what was the highest CO2 level in the past 800,000 years?
How do we figure past CO2 levels?
- Layers of ice are laid down each ear
- Bubbles of air get trapped as ice freezes
What is the modern CO2?
The patterns of variation between CO2 and temperature
- CO2 and temperature strongly co-vary
- As CO2 increases, temperature increases
Why does CO2 vary over time in absence of human activity?
The varying relationship between the Earth and Sun
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
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
How does solar radiation decrease due to solar cycles?
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
What positive feedback loop would increase in solar radiation result in?
What is linked to solar cycles that drove CO2 feedback loops?
- Long-term temperature changes
- CO2 feedback loops resulted in glacial and interglacial periods
Would you predict that modern CO2 levels are driven by feedback loops initiated by solar cycle changes?
- Current CO2 levels far above highest natural values for 800,000 years
What does the plotted lines suggest about temperature increase?
C) The most recent time interval best fit lines have higher, more positive slopes indicating more rapid temperature increase
Can modern warming be explained by solar activity?
- Until ~1960, warming and solar irradiance followed similar pattern
- Post 1960 -> solar irradiance would predict cooling while temperatures increased due to increased GHG concentrations
What will happen if we don't change our habits?
- Business as usual
- >8°F warming by end of century
- =4.5°C warming
What would happen if there was immediate and rapid emissions reduction
2.5°F warming by ending of century
- Short term variation in temperature and precipitation
- Varies hourly, daily, weekly, seasonally
- Weather systems=chaotic and unpredictable long-term
- Long term average weather conditions
- Predictable based on known factors that drive climate patterns
Persistent changes in average weather conditions
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
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