Transcript Introduction to Global Warming and Climate Change

Introduction to Global Warming
and Climate Change
APES/MOC/2007-2008
Factors That Affect Climate Changes
• Ice core data shows that Earth’s temperature
varies over time
– Earth’s energy balance and albedo surfaces
– Variation in insolation
– Milankovitch cycles
– Volcanoes, dust
– Ocean currents
– El Nino/La Nina cycles
Earth’s Energy Balance
Incoming solar radiation = energy reflected +energy absorbed
Scientists from the National Aeronautics and Space
Administration (NASA), The Earth Institute at Columbia
University, and Lawrence Berkeley National Laboratory
have confirmed that more energy is being absorbed from
the Sun than is emitted back to space, throwing the Earth's
energy "out of balance" and warming the planet. ( Using
satellites, data from buoys and computer models . )
Albedo: a measure of how much solar
energy is absorbed by a surface
Reds and oranges show high albedo where the surface is very absorbing
radiation, while blues and purples show surfaces that reflect more light.
Insolation Varies
• Normal variations in the sun’s radiation
• Known from ice core data
Q: Could reduced reflectivity, rather than
greenhouse gases, explain the Earth's
warming?
A: Scientists have concluded: after monitoring
the Earth's reflectivity for decades, changes in
our planet's reflectivity can't explain the
warming trend we currently are experiencing
Milankovitch Cycles
• Earth’s rotation and revolution combine to make the planet
“wobble” in its orbit
• This changes the position of the earth and affects seasonal
temperatures and albedo
• Such changes are believed to be principally responsible for
the waxing and waning of glacial periods (100,000 yr. time
spans) and normal climate cycles (20,000 – 40,000 year cycles)
• Milankovitch cycles have tremendous value as
a theory to explain ice-ages and long-term
changes in the climate
• they are unlikely to have very much impact on
the decade-century timescale of global
warming phenomenon
• http://apollo.lsc.vsc.edu/classes/met130/note
s/chapter16/graphics/71_Orbital_Fluctuations
/A_71.swf
Volcanoes and Dust
• Volcanic dust blasted into the atmosphere
causes temporary cooling. The amount of
cooling depends on the amount of dust put
into the air, and the duration of the cooling
depends on the size of the dust particles
• dust thrown up by windstorms or human
activity can affect the passage of heat and
light through the air
ENSO
• Climate “variability” are smaller-scale changes
in the energy balance
• Climate “change” may affect the intensity and
frequency of ENSO events
Ocean Currents
Because freshwater is less dense than seawater, increased precipitation,
melting of polar glaciers and ice caps could block the system by reducing the
amount of cold water that sinks downwards. Models currently predict a 25%
slow down of the Gulf Stream.
There is no doubt that climate has
natural variability over long periods
of time
HOWEVER: The most significant factor
attributing to global warming and climate
change at this time is believed to be the
rising amount of greenhouse gases, such as
carbon dioxide and methane, in the
atmosphere...
Greenhouse Effect: Natural Process
that moderates our climate and makes life possible on earth.
The Effect of Carbon Dioxide on Warming:
The greenhouse effect refers to circumstances where the
short wavelengths of visible light from the sun pass
through the atmosphere and are absorbed by the earth’s
surface.
•The longer wavelengths of the infrared re-radiation from
the heated surfaces are unable to pass through the
atmosphere.
•The trapping of the long wavelength radiation leads to
more heating and a higher resultant temperature.
•Carbon dioxide strongly absorbs infrared radiation, so
the greater the carbon dioxide the more infrared
absorption.
•This leads to greater heat retention in the atmosphere.
Human Impact on the Greenhouse
Effect
These are sketches of the
graphs produced in the
IPCC 2007 report of the
increase in key
greenhouse gases. They
make clear that most of
the increase of the last
thousand years has
occurred in the past 200
years.
From 1980 to the end of the 21st century,
temperatures are projected to increase by
1.8°C to 4.0°C.
IPCC Conclusions
•
•
•
•
Current warming trends are unequivocal. It is very likely that greenhouse gases released by human
activities are responsible for most of the warming observed in the past fifty years. The warming is
projected to continue and to increase over the course of the 21st century and beyond.
Climate change already has a measurable impact on many natural and human systems: snow and ice are
melting and frozen ground is thawing, hydrological and biological systems are changing and in some cases
being disrupted, migrations are starting earlier, and species' geographic ranges are shifting towards the
poles. Effects are projected to increase in the future and to be more severe with greater increases in
temperature. Adaptation measures are already being implemented, and will be essential in order to
address the projected consequences. There is, however, a limit to adaptation; mitigation measures will
also be needed in order to reduce the severity of impacts. (NOTE: difficult to separate natural variability
from climate change effects, more research needed).
Mitigation measures that aim to reduce greenhouse gas emissions can help avoid, reduce or delay many
impacts of climate change. Policy instruments could create incentives for producers and consumers to
significantly invest in products, technologies and processes which emit less greenhouse gases. Without
new mitigation policies, global greenhouse gas emissions will continue to grow over the coming decades
and beyond. Rapid world-wide investments and deployment of mitigation technologies, as well as
research into new energy sources will be necessary to achieve a stabilization of the concentration of
greenhouse gases in the atmosphere.
Additional research addressing gaps in knowledge would further reduce uncertainties and thus facilitate
decision-making related to climate change.
ADAPTATION and MITIGATION
ADAPT: coastal defenses, government response
to heat waves and flooding, technology
solutions, modify consumption habits
MITIGATE: reduce greenhouse gas emission
• Kyoto (international cooperation); individual
government policies to reduce emissions