4. Human’s Experiment with Climate
• Increased concentration of GHG’s in the
atmosphere due to human activities
• Burning of fossil fuels
• Deforestation
• Landfills
• Fertilizer use
• Livestock production
• Since the early 20th century, average
global temperatures have increased
nearly 1.4 degrees F
• Warming will have widespread impacts
on human life and natural ecosystems by
2100
6. What the Past Tells Us
• 350 years ago the world was in the
depths of a prolonged cold spell
called the ‘Little Ice Age’
• 20,000 years ago, in the middle of
the last glacial period, large
continental scale ice sheets
covered much of North America,
northern Europe and northern
Asia
• 50,000,000 years ago, global
temperatures were so high that
there were no large ice sheets at all
7. Paleoclimatology
The study of past climates
• Anthropology
• Geology
• Chemistry
• Biology
• Atmospheric Science
• Oceanic Science
• Physics
• History
10. Timeline of Extreme Warming Events
PETM; 66-34Ma
The Neoproterozoic; 1000-500Ma
Huronian Warming Event; 4.6Ba
Cambrian Explosion!
Extinction of
Dinosaurs!
11. What Causes Ice-Ages and
Warm Periods?
Dynamic interactions between;
• Solar output
• Distance of Earth from Sun
• Position of continents and
topography
• Ocean circulation
• Composition of atmosphere
12. Cryogenian Ice-Age
850-630Ma
• Continents clustered at
low-latitudes
• Ice-sheets build up in
polar oceans
• High albedo- light
reflecting back to space-
enhances cooling
• Sea ice reached past 30
degrees latitude and
continued to grow
• Run-away albedo effect
• Ice engulfed planet at
average depth more than
1km
13. Leaving Snowball Earth
The Geochemical Carbon Cycle
• Plate tectonics continue
• Volcanoes continue to vent
CO2
• Little water would
evaporate earth’s surface
so no rainfall to wash CO2
out of atmosphere
• Over 10Ma, volcanic
activity increase CO2 by a
factor of 1,000, triggering
extreme warming
• Intense rainfall and
evaporation
• Accelerate rock
weathering, bringing CO2
to normal range
14. Why does this matter?
• What happened?
• Why did it happen?
• Has it happened before?
• Will it happen again?
• How do we know about it in the first place?
15. Paleoclimate Data
• Isotopic geochemistry; carbon and oxygen
• Dendrochronology; tree rings
• Pollen Distribution; found in sediments, ice,
rocks, caves, etc
• Lake Varves; annual mud layers
• Coral bed rings
• Fossils
• Human documents, paintings, evidence of
civilization
17. What can
they tell us?
Tree Rings & Dendrochronology- the annual growth rings of trees from
mid-latitude climates, where a warm growing season alternates with a
winter of dormancy, tell us about temperature, precipitation, and other
factors that affect plant growth rates.
Ice Cores- long, cylindrical cores of ice drilled from glaciers and the ice
caps of Greenland and Antarctica have annual bands. The layers in the ice
tell us about temperature and precipitation. Gas bubbles trapped in the ice
provide data about atmospheric CO2 composition in the past.
Sediments from beds of lakes and oceans- Layer thickness can indicate
amounts of precipitation or meltwater runoff as rivers carry sediments
downstream. Chemical and isotopic composition of the shells of
microorganisms embedded in sediments can tell us about the temperatures
when those shells were made.
18. What can
they tell us?
Coral reefs - corals form annual growth bands. Analysis
of ratios of different types of oxygen in minerals in corals
tells us about sea temperatures, although variations in
salinity can make these records more difficult to interpret.
Pollen - the amounts and types of pollens found in
sedimentary deposits tell us about the types of vegetation
found in a certain area at a given time. The vegetation that
grows in a place indicates the climate of that place, since
different plants grow in differing conditions of
temperature, moisture, etc.
Fossils - knowledge of the conditions in which various
animals and plants thrive, or at least survive, allows us to
use fossils from sedimentary rocks as climate indicators.
19. The Sahara wasn’t a desert
9,000 years ago….
How do we know?
Deep sea sediment cores revealed
low salinity= lots of water! When it’s
dry and water evaporates, it leaves
behind salt.
Fossil leaf waxes found in ancient
lake sediments have low isotopic
composition
Pollen records in sediment cores
from Lake Tang were of plants that
thrive in humid conditions
Intense Monsoonal Rains
Steppe, covered in grasslands and shrubs.
Dotted with large and small lakes
20. ~5,200 years ago
It was cold and dry!
Preserved plants in Quelccaya ice cap in the
Peruvian Andes carbon dated to 5,200 years
Oetzi the Ice-man discovered in
Europe in 1991 trapped and died
5,200 years ago
Tree rings from Ireland and
England were at their narrowest
5200 years ago, which suggests the
driest period they experienced
Ice cores showing two oxygen isotope
ratios from the top of Mt. Kilimanjaro in
Africa revealed that temperatures 5,200
years ago were very cold!
Changes in plant pollen from lakebed cores
in South America, lowest levels of methane
retrieved from ice cores from Greenland and
Antarctica, both occurred 5,200 years ago
21. Paleocene Eocene
Thermal Maximum
55 Ma
• Global average temperature of
74F
• Poles were free of ice-caps
• Palm trees and crocodiles were
found in the arctic circle
• > 5 degrees C of warming in
15,000-20,000 years
22. PETM as Analog for
Current Trends
Warming today is happening
ten times as fast!
We are headed for a tripling
or quadrupling of CO2 from
preindustrial levels
25. The Critics…. • We don’t have reliable data
• There is no evidence
• Glaciers have always grown and receded
• One hundred years isn’t enough to give us an
accurate measure
• Not every region of the world is warming
• We can’t even predict the weather next week
• Natural emissions dwarf human emissions
• Current warming is a natural trend
26. What Can WE do?
What is Earth’s Climatic Fate?
Editor's Notes
Earth’s climate is a dynamic system that is driven by energy from the sun and constantly impacted by physical, biological and chemical interactions between the atmosphere, global water supplies, and ecosystems
Energy reaches earth in form of solar radiation
Water vapor, clouds and heat trapping gases create natural greenhouse effect by holding heat in atmosphere and preventing release back to space
Planets surface then warms, increasing heat emitted so that energy released back from earth to space balances what earth receives as visible light from sun.
With human activities today boosting atmosphere GHG levels, earth retatin fraction of energy from sun, raising temperatures---ANTHROPOGENIC CLIMATE CHANGE
Ask attendees to share examples
What changes in climate have people experienced? Blizzard of 77, drought, etc.
Yearly oscillations in the curve reflect seasonal cycles in the northern hemisphere, which contains most of Earth’s land area. Plants take up CO2 during the growing season in spring and summer and release it as they decay in fall and winter.
Throughout much of it’s history, Earth’s climate has alternated between periods of warmth and relative cold, each lasting tens to hundreds of millions of years.
From the perspective of geological time, our planet is currently passing through a relatively cold phase in its history and has been cooling for the past 35 million years
Cold phases, ice sheets covered most of the mid-latitudes, warm phases, forests extended all the way to the poles
First evidence to support climate change theories
Fossils of a temperate forest were discovered sandwiched between ice age soil layers
First evidence to support climate change theories
Began in the Early 1800’s
Pointed to glaciation
Misplaced boulders scattered across much of the northern hemisphere
Long scratches marked exposed rocks on valley floors
Banded Iron Formations; layers of Banded iron interspersed with chert. Iron only forms in anoxic conditions so our oceans now aren’t forming iron.
Also during cretaceous, found oldest flowering plant, dating at 122 million years old.. Closest relative is the black pepper plant
Make connection to good and bad for global warming. New life… but also death!
Variations in Earth’s orbit, which involve the tilt of the earth’s pole of rotation and the ellipticity of earth’s orbit 100,000 41,000, 23,000 year cycles
Talk about plate tectonics briefly!
Positive feedbacks amplify them; albedo and composition of atmosphere
Change in solar energy and Earth’s orbit could have caused initial cooling.
Ice sheets form closer to equator, where sunlight is more direct.. More cooling!
Preserved physical characteristics of the past that are used to infer and reconstruct past climatic conditions. derived from natural sources such as tree rings, ice cores, corals, and ocean and lake sediments.
These proxy climate data extend the archive of weather and climate information hundreds to millions of years.
The data include geophysical or biological measurement time series and some reconstructed climate variables such as temperature and precipitation.
These proxy climate data extend the archive of weather and climate information hundreds to millions of years.
The data include geophysical or biological measurement time series and some reconstructed climate variables such as temperature and precipitation.
Bristlecone Pine: 5400 years old!
Oldest dated tree– 10,000
Instrumental: Recorded like temperature, amount of rainfall, humidity
Historical: observational rain vs. frost vs. snow, timing of droughts and floods, flowering of trees, migration of birds.
From further research however… its transition into the dry climate that exists today happened in just decades!
Pangaea in final stages of breaking apart
Rapid release of Carbon found in sediment cores.
Broke apart frozen seafloor releasing extreme amounts of methane
Ocean turned acidic, planet warms up dramatically. Extinction of marine foraminifera and difficult for corals. Rapid change in land plants and animals and quick turnover of species.
( Deep sea lake sediments; low oxygen isotopes=warm, decrease in heavy carbon isotopes =release of CO2 in atmosphere )
Warming lasted 200,000 years before earth was able to stabilize again
People could argue– warmer temperatures… bringing new life! But is it happening too quickly for life to adapt?
CO2 on the rise since the end of the last glacial maximum….. But look how our levels compare with history of Quaternary glaciations!
