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Chapter 9

ENVS 137 Chapter Notes - Chapter 9: Sea Level Rise, Erms, Kyoto Protocol


Department
Environmental Science
Course Code
ENVS 137
Professor
zahina-ramos
Chapter
9

Page:
of 7
CHAPTER 9: CLIMATE CHANGE AND GLOBAL WARMING
9.1: Long-Term Climate Patterns
Climate change - variations/ long term changes in climate
The Pleistocene - The Last 2 Million Years
Pleistocene epoch - For nearly 2 million years, Earth’s climate has cycled between
cold (ice ages) and warm periods (interglacial periods) each cycle lasting about 100,000
years
Cold periods → sea level dropped (water froze in glaciers)
Changes in Earth’s orbit that influence the amount and distribution of solar radiation
caused these cycles → affect the average amount and distribution of solar radiation
striking Earth’s surface
Milankovitch cycles - shifts from glacial to interglacial conditions
Accumulation of snow and ice → reflect more of sun’s energy → land absorbs less heat
→ Earth cools → allows ice to grow and spread (speeds cooling process)
Changes in ocean currents can also contribute to spread of glaciers
Volcanoes spewing ash into the air
Changes in chemical composition of Earth’s atmosphere (air bubbles trapped in each
layer of ice)
Concentrations of CO2 much lower during cold glacial periods
Decreased CO2 concentrations → less heat trapped → additional cooling during
glacial periods
Holocene - The Last 10,000 Years
Periods of warming and cooling have produced different climate patterns in specific
regions
The Big Freeze - 12,000 years ago
Holocene epoch - last 10,000 years - Earth has been in a warm interglacial period
Medieval Warm Period - AD 1000-1300 → average global temperatures increased →
caused by decreased volcanic activity and increase in solar radiation
Little Ice Age - AD 1400-1700 → cold period caused by eruptions of four very large
tropical volcanoes
Currently Earth’s atmosphere is warming at a rate faster than any previous time in the
Holocene
Anthropocene - current warming era?
9.2: Measuring Global Temperature
Long term trends in global temperature → inferred from changes in fossils and chemical
isotopes found in sediments and glacial ice
Climate change during the last 3,000 years → estimated from tree growth, measured by
width of annual rings
Earth’s temp has warmed by 1-2 degrees C since the late 1800s
warming more intense in some regions than others
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Changes in ocean currents and events such as volcanic eruptions complicate the pattern
of global warming
Measuring Climate Change
Since the beginning of the Industrial Revolution, Earth’s atmosphere has warmed
significantly
Not exactly accurate data but scientist study patterns
Temperature anomaly - the difference between each year’s average temperature and
the benchmark (the average annual temp for each location over a specific time interval)
Positive - a year that is warmer than the benchmark
Negative - a year that is cooler than the benchmark
Anomalies averaged in many locations → measure of global temp
Global warming - a specific climate trend - the increase in atmospheric temperature
since the late 1800s (coincides with the Industrial Revolution)
Causes of Natural Climate Variation
Temperature trends vary among regions and from year to year
Solar forcing - the phenomenon of changes to climate brought about by changes in
solar radiation
Explanation for current warming trend
But solar radiation output decreased over past 50 years (sunspots)
Small impact
Regional variations on land
b/c circulation patterns in troposphere and ocean currents (move heat from the
equator to the poles)
Intensifies temperature change in the polar regions → accelerated climate
change in Arctic ecosystems
Temperature anomalies generally higher over interior of continents (b/c
continental regions heat up more quickly than nearby oceans)
Regional variations in sea surface temperatures
Changes in currents
El nino / Southern Oscillation (ENSO) - changes in sea surface temperatures
over large regions that occur over intervals of years or decades → affect weather
conditions around the world
Volcanic eruptions
Add tons of sulfur dioxide to the lower atmosphere → particles reflect sun’s rays
and cool the atmosphere
9.3: Causes of Global Warming
Human contributions:
Chemical composition of the troposphere
Reflectivity of Earth’s surface
Deforestation and burning of fossil fuels → large quantities of CO2
into the
atmosphere
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Industrial and agricultural activities → release methane
and nitrous oxide
(absorb disproportionate amount of the infrared radiation emanating from Earth’s
surface and trap it as heat)
The Greenhouse Effect
Some gas molecules trap heat radiated from Earth’s surface in the lower atmosphere
Greenhouse gases - gases that efficiently capture heat
H2O and CO2 have an impact on the atmospheric temperature far in excess of
their relative abundance (trap more heat) than O2 and N2 (which make up 99%
of the atmosphere)
Most abundant greenhouse gas is water vapor
Warmer air → more evaporation → more water vapor → clouds → cool Earth’s
surface temp
CO2
Methane - released from decomposition of vegetation
Nitrous oxide - natural by-product of the nitrogen cycle
Without them the world would be frozen
Greenhouse effect - the trapping of heat in the troposphere by greenhouse gases
Human Impacts
Human activities have increased the abundance of several greenhouse gases in the
atmosphere
Agriculture (burning forests), livestock, burning charcoal, burning of fossil fuels
→ Anthropogenic
(human caused) greenhouse gas emissions
Also emit synthetic greenhouse gases (CFC → hole in ozone)
Impact of the emission of different anthropogenic greenhouse gases depends on 2
factors:
1. Their capacity to absorb infrared light and retain heat
2. The length of time they stay in the atmosphere (atmospheric residence time)
→ used to calculate a molecule’s global warming potential (GWP) (measure of an
individual molecule’s long-term impact on atmospheric temperature)
GWP calculated relative to CO2 (GWP 1) → stays in atmosphere for 100 years
Global warming is a direct consequence of the increased amount of greenhouse gases
in Earth’s atmosphere → linked to human activities
Burning of fossil fuels
Deforestation
Pollution from industry and agriculture
Forest fires and the burning of fuelwood, diesel release black carbon (solid
particles) → absorb incoming solar radiation and directly warm the atmosphere,
reduce reflectivity of the surfaces they settle on → warming
Sources of Greenhouse Gas Emissions
Carbon dioxide equivalents (CO2e) - terms in which scientists express total
greenhouse gas emissions → take in GWP of each gas
CO2 = 65% of warming
Fossil fuels (coal and natural gas)
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