changing faster today than at any other time cause – human activity (anthropogenic)
TRANSCRIPT
GLOBAL CHANGE
Changing faster today than at any other time
Cause – human activity (anthropogenic)
GLOBAL CHANGE
Greenhouse Gases & Greenhouse Effect
GLOBAL CHANGE
Destruction of Ozone Layer
GLOBAL CHANGE
Loss of Biodiversity
GLOBAL CHANGE
Global Environmental Issues◦ Need to be informed to make intelligent decisions
Global Change in the Past◦ Need to understand how planet was changing
before humans◦ Global change can occur on short (1000’s years)
or long (millions of years) time scales The Earth System
◦ Different components of Earth interact in response to forcings (internal and external influences)
THREE MAJOR THEMES
Global warming – an increase in Earth’s surface temperature caused by industrial and agricultural activities◦ Release gases that increase greenhouse effect◦ Intergovernmental Panel on Climate Change
(IPPC) – 2007 “Warming of the climate system is unequivocal, as it
is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.”
GLOBAL CHANGE – SHORT TIME SCALE
Measuring Atmospheric CO2 – The Keeling Curve
1958 – 315 ppm 2008 – 386 ppm
◦ 1 cc of air = 2.7 x 1019 molecules◦ 1ppm concentration = 2.7 x 1013 molecules
Most increase due to combustion of fossil fuels (coal, oil, natural gas)◦ Tropical deforestation also contributes
Trend of increasing atmospheric CO2 is real
Measuring Atmospheric CO2 – The Keeling Curve
Climate Proxy Data
Use air bubbles trapped in polar ice◦ Matches direct measurement well – reliable
technique for determining long-term CO2 concentrations
Pioneer Effect◦ 1800-1850 (before Industrial Age)◦ Increased CO2 due to deforestation of American
West
Measuring Atmospheric CO2 – Ice Cores
Methane (CH4) & Nitrous Oxide (N2O) – from agriculture
CFCs (Chlorofluorocarbons) – destroy stratospheric ozone too
HUMANS HAVE ALTERED EARTH’S ATMOSPHERE
OTHER GREENHOUSE GASES
Global Mean Surface Temperature◦ increased 0.8 ℃ since 1900
SURFACE TEMPERATURE
Understand the past in order to predict the future◦ Little Ice Age (1500-1850)
Understand the whole Earth system in order to correctly interpret the changes that are occurring◦ Sulfate aerosols
Understand the time scales on which global change occurs◦ Sulfate aerosols removed in weeks, CO2 stays for
centuries
NECESSITIES
Warming at the poles could raise sea level◦ Greenland ice cap – sea level increase 6 meters
(20 feet)
CRYOSPHERE CHANGES
Rise in sea level◦ 10 cm in last 100 years
Thermal expansion Melting ice Impact agriculture
◦ Decreased soil moisture◦ Spread of tropical pests
Stronger hurricanes Earth has been significantly warmer in the
past – past is the key to the present
CONSEQUENCES OF GLOBAL WARMING
1985 – discovery of ozone hole above Antarctic
1975-1990 – ozone dropped by half (October)
Inverse relationship between ozone and ClO (chlorine monoxide)
OZONE DEPELTION
Humans have been altering the land surface for 10,000 years
Tends to reduce complexity of landscape Reduces biodiversity
◦ Change in land can cause species unable to move ore adapt to become extinct
◦ Genetic information lost Currently, greatest loss of species is in the
tropical rainforests◦ Rainforests most biodiverse habitats◦ Rainforests disappearing the most
DEFORESTATION ANDLOSS OF BIODIVERSITY
Ozone Depletion?◦ Omit CFCs - recovery in 50-150 years
Increased CO2?◦ Stop CO2 emissions – recovers in 1-2 million years
Loss of Biodiversity?◦ Mass extinction – never recovers completely
OF MOST CONCERN?
Glacial-Interglacial cycles Mass Extinctions Solar Luminosity Change
PAST GLOBAL CHANGE
The Geologic Time Scale –◦ Divisions based on appearance/disappearance of
organisms◦ Earth is 4600 million years old (4.6 billion)◦ Most of Earth time before animals with
preservable hard parts appeared Cambrian 544 mybp Precambrian 544-4600 mybp
HOW LONG IS LONG?
Antarctica Vostok and Dome C 800,000 years CO2 concentrations Temperature
◦ Based on deuterium Glacial/Interglacial
Periods◦ Last Ice Age ended
11,000 years ago
Ice-Core Temperature Record
Surface Temp , CO2 & CH4 ◦ associated with interglacial periods
21,000-11,000 ybp & 140,000-130,000 ybp
Why would CO2, CH4 & temperature co-vary?◦ Greenhouse Effect◦ Change in deep ocean circulation due to change
in climate (brings more CO2)
Atmospheric CO2 affects climate and climate affects atmospheric CO2
ICE CORE RESULTS
65 mybp◦ Dinosaurs extinct◦ 60-80% of marine species extinct◦ Numerous terrestrial organisms
WHY?
MASS EXTINCTION
Clay layer at K-T boundary Walter & Luis Alvarez
◦ Use iridium to determine rate of clay deposition◦ Iridium 100 x higher than expected◦ Iridium uncommon on Earth – reasoned that it came
from the impact of a large extraterrestrial object
K-T Mass Extinction
The Earth system has recovered from large shocks in the past◦ Recovery is slow◦ Recovery generates a modified Earth
MASS EXTINCTIONS
As the sun ages and uses up its hydrogen fuel – its luminosity (brightness) increases◦ 4,600 mybp Sun was 30% dimmer (less luminous)◦ Luminosity has increased slowly, then rapidly◦ Currently brightness increases 1% /100 x 106
years◦ In 5,000 my – 2-3 times brighter than now
Early Earth colder (if other factors constant)◦ Ocean should have been frozen – BUT NO
3.8 bya – sedimentary rocks 3.5 bya – organisms
◦ Faint Young Sun Paradox – solution? Higher levels of Greenhouse gases in early
atmosphere
SOLAR LUMINOSITY
James Lovelock & Lynn Margulis Earths is a self-regulating system in which the
biota play an integral role◦ The biota manipulate the environment for their own
benefit, or by optimizing the conditions for life, for the benefit of all living organisms
Life itself is responsible for maintaining the stability of Earth’s climate
Climate stability implies self-regulation◦ Biotic feedbacks (Gaia Hypothesis)◦ Abiotic feedbacks (carbonate-silicate geochemical
cycle)
GAIA HYPOTHESIS