Chemical Cycles:
•Greenhouse Effect: Cause and effect •Chemical Cycles: CO2 and O2 •Chemical Fluxes: CO2 and O2 •Proxies for climate change: Isotopes...
E from surface absorbed by GH gas GH gas re-radiate the E, heating atm. & surface
Natural process! W/out it, 30ºC cooler
Goldie Locks Effect
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If Earth was 17% closer to sun, then liquid water would not form on surface. Thus no CO 2 dissolved in oceans and E would be hot enough to melt Lead….Like Venus is. If Earth was further from sun, then solar radiation would be lower and E would be and ice house like Mars.
Observed increase in GH gases Direct measurement Mona Loa
Ice core data
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Observed Effects of GH
Global Warming by 0.3-0.6ºC! Receading Glaciers & Ice caps - past 100 yr Rising Sealevel - 18 cm in 100 yrs (greatest rate in E history)!
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Some would argue the Global Warming trend is natural - not forced by human activity. • •
Some argue that solar activity is linked to global warming. In the geologic past this is true: Global trends in temperature proxies sometimes correlate with solar activity and cosmogenic nuclide abundances (e.g. 36Cl) •
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E.g. Midieval Warm period (900-1400 A.D.) and the Little Ice Age (1500-1800 A.D.) However, this is not true of today’s warming trend: there is no measurable increase in 36 Cl abundance over the past century. Measurable variability in solar activity after 1978 accounts for ~0.01% of total irradiance.
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Some would argue the Global Warming trend is natural - not forced by human activity.
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Long-term trends in temperature proxies sometimes correlate with Earth orbital cycles called Milankovitch cycles (e.g. the last ice age)
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The cause of today’s climate change is the greenhouse effect!
However, this is not true of today’s warming trend - it is much to rapid to correlate with variations in Earth’s orbit
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This is the overwhelming consensus of the scientific community.
AGU’s position
Observed Results of GH • • •
Global Warming by 0.3-0.6ºC (avg surface T)! Receding Glaciers & Ice caps - past 100 yr Rising Sea level - >20 cm in 100 yrs (greatest rate in E history)! • • •
Averaging ~1.8 mm/y from 1950 to 2000 Rising faster today Mostly from thermal expansion of ocean, not added melt water
Observed results of GH: Loss of Sea Ice
• Effects polar bears: 2006 study showed predation and cannibalism within Beaufort Sea population. In past 5 years, 43% of cubs survive compared to 65% between 19801990 •Barnes Ice Cap on Baffin Island is thinning (0.12 m/y ‘70-’84) accelerating (1.0 m/y ‘04-’06). Correlates with increases in number of positive degree days (warming).
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Observed results of GH: Increased hydrologic cycle
Cyclone activity
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Increase in number of category 4 and 5 cyclones over past 35 yrs. Increase in the duration of cyclones over past 35 yrs. Extreme rain events during Indian Monsoon between 1951-2001 • 10% Increase in frequency of intense rain events (>10 cm/day) • Increasing magnitude of intense rain events • Total amount of precipitation not increasing • •
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Global Dimming - may have muted global warming •
Aerosols in atmosphere increase Earth’s albedo •
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Carbon aerosol
Particles reflect sunlight
Between 1960 and ~1985, increase in aerosols caused ‘dimming’ of ~3 to 6%
S-dioxide aerosol
•~1985 to early ‘90s Earth began to brighten again
~1985 to early ‘90s Earth began to brighten again Decreasing aerosol emissions Improved air-quality regulations • Reduced Pinatubo (volcanic) aerosols - 1991 eruption • •
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This correlates with the rapid increase in temperature during the 1990s
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Predicted Effects of Global Warming • •
Increasing Global Temperatures Stabilizing our climate will require near-zero emissions (GRL, 2008) Model result GH gasses remain in atm for centuries • Must stop emissions to prevent warming beyond today’s temperatures • Not possible given energy needs and sources • •
Predicted Effects: Shifts in climate zones
Predicted Effects: Continued rise in sea level
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Consider how this will effect coastal communities. Bangladesh: 1000 people/km 2
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Predicted Effects: Extreme Weather
Heightened hydrologic cycle (greater rainfall and snowfall) Recall Current Observations of Cyclones and Monsoon events above.
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Predicted Effects: Negative impact on marine ecosystems Increasing CO 2atm increases amount of CO 2 in oceans. This decreases pH of oceans (making them more acidic) Harmful to Plankton and Coral
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These form the base of the marine food web!
Prediction - Harmful conditions will develop first in southern ocean within decades.
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Nature, 2005
Predicted Effects: Negative impact on marine ecosystems
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Measured decline in productivity in all oceans Area of low productivity (
