Global warming is caused primarily by human activity like the burning of fossil fuels which increases greenhouse gases in the atmosphere like carbon dioxide and methane. The main effects are the greenhouse effect, where gases trap heat radiating from the Earth and solar variations which have contributed to increased temperatures in recent decades. Positive feedback loops from melting permafrost and sea ice also accelerate global warming further if not curtailed. While pollution caused some global dimming in the past, addressing only greenhouse gases is needed to avoid catastrophic warming this century.

1. Global Warming
Submitted by
Harshit Bairwa (18)
Gitika Singh (16)
Guided by- prof Priya

2. Causes
Including:
Greenhouse Effects
Solar Variations
Feedbacks
Global Dimming
Mostly from human activity

3. Causes
 The world's leading climate scientists said global warming has begun, is
very likely caused by man, and will be unstoppable for centuries. The
phrase very likely translates to a more than 90 percent certainty that
global warming is caused by man's burning of fossil fuels. That was the
strongest conclusion to date, making it nearly impossible to say natural
forces are to blame.
 The scientists said global warming's connection varies with storms in
different parts of the world, but that the storms that strike the Americas
are global warming-influenced.
- The New York Times Report

4. Causes ~ Greenhouse Effects
 Emission of infrared
radiation.
 Greenhouse – house
heated up by solar
radiations. For
planting plants,
warms air near
ground, trapping air
from rising and
flowing away.

5. Causes ~ Greenhouse Effects
 Discovered by Joseph
Fourier in 1824.
 Planetary energy
balance. Planets lose
energy by chaleur
obscure.
 Balance reached
between heat gain and
heat loss.
 Later, known as Stefan–
Boltzmann law (50 years
later).

6. Causes ~ Greenhouse Effects
 Later, described qualitatively
by Svante Arrhenius.
 First man who speculated
changes CO2 in the
atmosphere could
substantially alter the surface
temperature through the
greenhouse effect. ["On the
Influence of Carbonic Acid in
the Air Upon the
Temperature of the Ground",
Philosophical Magazine
1896(41): 237-76]
 Formulated Arrhenius'
greenhouse law
if the quantity of carbonic acid
increases in geometric
progression, the augmentation of
the temperature will increase
nearly in arithmetic progression.

7. Causes ~ Greenhouse Effects
 Intergovernmental Panel on Climate Change
Fourth Assessment Report. (Chapter 1:
Historical overview of climate change science)
said that average earth surface temperature is
15 °C (33 °C warmer without Greenhouse
Effects)
 Increasing Greenhouse
Gasses causes
Global Warming.

8. Causes ~ Greenhouse Effects
 Greenhouse gasses –
components of
atmosphere that
contribute to
greenhouses effects.
 include in the order of
relative abundance
water vapour, carbon
dioxide, methane,
nitrous oxide, and
ozone.

9. Causes ~ Greenhouse Effects

10. Causes ~ Greenhouse Effects
 Measurements of Pollution in
the Troposphere
MOPITT carbon monoxide over
India
MOPITT 2000 global carbon monoxide

11. Causes ~ Greenhouse Effects
 Increases in carbon dioxide cause the earth to get
warmer
 Greenhouse gases in the atmosphere absorb heat
radiating from the earth.
 This trapped heat increases the evaporation of water
from the oceans into the air to cause a greater
increase in warming of the atmosphere. CO2 has a
forcing effect on climate.
 The combined effect of water vapor, carbon dioxide
and methane controls the temperature of the earth.

12. Causes ~ Greenhouse Effects

13. Causes ~ Greenhouse Effects
 CO2 level is
increasing in the
atmosphere
 CO2 is produced by
burning woods etc
 Current level
280ppm to 370ppm
 This increase →
increase heat absorb
by the earth

14. Causes ~ Greenhouse Effects
IPCC predicts atmospheric
concentration of CO2: 541ppm to 940 in
2100.
Fossil fuel reserves are sufficient to
reach this level and continue emissions
past 2100, if coal, tar sands or methane
clathrates are extensively used.

15. Causes ~ Greenhouse Effects

16. Causes ~ Solar Variation
 Few paper claim that
Sun’s also contribute to
increase global
temperature.
 About 40% to 50% in
1900 - 2000 and 25% to
35% in 1980 – 2000.
 Cooling effect from
volcano dusk and sulfate
aerosols .

17. Causes ~ Solar Variation
 Galactic Cosmic Rays
 Magnetic activity of the sun is
a crucial factor which deflects
cosmic rays that may
influence the generation of
cloud condensation nuclei
and thereby affect the
climate.
 Warming most of
stratosphere (greenhouse
gas theory predicts cooling
here)
 Reduction of stratospheric
ozone has cooling influence

18. Causes ~ Solar Variation
 Solar variation combined with
changes in volcanic activity.
 Pre-industrial times to 1950:
warming effects
 Then, it’ll be cooling effect
 Researchers claim that no
net increase of solar
brightness over the last
thousand years.
 BUT, solar cycles led to a
small increase of 0.07% in
brightness over the last thirty
years.

19. Causes ~ Solar Variation
 Sami Solanki, the director of the Max Planck Institute for
Solar System Research in Katlenburg-Lindau, Germany
said:
 “The sun has been at its strongest over the past 60 years
and may now be affecting global temperatures... the
brighter sun and higher levels of so-called "greenhouse
gases" both contributed to the change in the Earth's
temperature, but it was impossible to say which had the
greater impact”

20.  Solanki agrees with the scientific consensus that the marked upswing in
temperatures since about 1980 is attributable to human activity.
 "Just how large this role [of solar variation] is, must still be
investigated, since, according to our latest knowledge on the variations
of the solar magnetic field, the significant increase in the Earth’s
temperature since 1980 is indeed to be ascribed to the greenhouse effect
caused by carbon dioxide."
 Stott's 2003 work mentioned in the model section above largely revised
his assessment, and found a significant solar contribution to recent
warming, although still smaller (between 16 and 36%) than that of the
greenhouse gases.

21. Causes ~ Feedback
 Methane release from
melting permafrost peat
bogs
 Western Siberia – world
largest peat bogs.
 Formed last 11000
years ago (end of Ice
Age)
 Expected to release
70,000 tonnes methane
in next few decades

22. Causes ~ Feedback
 Methane release from
hydrates
 Methane clathrate water
ice which contains a
large amount of
methane.
 Can be found on ocean
floor.
 The sudden release of
Methane hydrates could
cause runaway
greenhouse effects.

23. Causes ~ Feedback
 According to the clathrate
gun hypothesis a runaway
greenhouse effect could be
caused by liberation of
methane gas from hydrates
by global warming if there are
sufficient hydrates close to
unstable conditions.
 Melting permafrost peat bogs
and methane hydrate.
 Methane being 21-times
more potent a greenhouse
gas than carbon dioxide

24. Causes ~ Feedback
 Carbon cycle feedbacks.
 Cause loss of carbon from
terrestrial ecosystems, leading to
an increase of atmospheric CO2
levels.
 One model in particular
(HadCM3) indicates a secondary
carbon cycle feedback due to the
loss of much of the Amazon
rainforest in response to
significantly reduced precipitation
over tropical South America.
 Researchers suggest any such
feedback would accelerate
global warming.

25. Causes ~ Feedback
 Forest Fires
 Releasing carbon in the
atmosphere than the
carbon cycle can
naturally re-absorb.
 Rising global
temperature might
cause forest fires to
occur on larger scale,
and more regularly.

26. Causes ~ Feedback
 Retreat of sea ice.
 The sea absorbs heat from
the sun, while the ice largely
reflects the sun rays back to
space.
 Retreating sea ice will allow
the sun to warm the now
exposed sea water,
contributing to further
warming.
 Think of Black Car heats up
faster then White Car.
 The trend for global sea ice,
northern hemisphere and
southern hemisphere
combined is clearly a decline.

27. Causes ~ Global Dimming
 Burning of fossil
fuels is creating two
effects:
 Greenhouse gases
that cause global
warming
 By-products which
are pollutants that
cause global
dimming

28. Causes ~ Global Dimming
 Global dimming is the gradual
reduction in the amount of global
direct irradiance at the Earth's
surface that was observed for
several decades after the start of
systematic measurements in 1950s.
 Caused by an increase in
particulates such as sulfur aerosols
in the atmosphere due to human
action.
 4% reduction over the three decades
from 1960–1990.
 This trends is reversed from past
decades.
 Interfered with the hydrological cycle
by reducing evaporation and may
have caused droughts in some
areas.
 Cooling effect: Greenhouse effects

29. Causes ~ Global Dimming
 Fossil fuel use, as well as
producing greenhouse gases,
creates other by-products.
 These by-products:
Pollutants.
 These pollutants: change the
properties of clouds.
 Polluted air results in clouds
with larger number of
droplets than unpolluted
clouds → clouds more
reflective.

30. Causes ~ Global Dimming
 Climatologists studies:
reflection of heat made
waters in the northern
hemisphere cooler.
 Resulting less rain in
Northern Africas.
 What came out of our
exhaust pipes and power
stations contributed to the
deaths of a million people in
Africa, and afflicted 50 million
more with hunger and
starvation.
 The Asian monsoons bring
rainfall to half the world’s
population.

31. Causes ~ Global Dimming
 After 911, all commercial
flights were grounded for
the next three days.
 Which allows climate
scientists to look at the
effect on the climate
when there were no
contrails and no heat
reflection.
 Result: Temperature is
up 1 degrees in three
days.

32. Causes ~ Global Dimming
 Currently, most climate
change models predict a 5
degrees increase in
temperature over the next
century, which is already
considered extremely grave.
 However, global dimming has
led to an underestimation of
the power of global warming.
 Global dimming can be dealt
with by cleaning up
emissions.

33. Causes ~ Global Dimming
 Europe 2003.
 various measures have been
taken to clean up the emissions
without reducing the greenhouse
gas emissions in parallel.
 Effects:
 This may have already
lessened the severity of
droughts and failed rains in the
Sahel.
 Contributed to European heat
wave in 2003 that killed
thousands in France, saw
forest fires in Portugal, and
caused many other problems
throughout the continent.

34. Causes ~ Global Dimming
 Addressing global dimming only
would increase global warming
more rapidly.
 Irreversible damage would be
only about 30 years away.
 The melting of ice in Greenland.
 Drying tropical rain forests would
increase the risk of burning.
Releasing more CO2.
 These and other effects could
combine to lead to an increase of
10 degrees centigrade in
temperature over the next 100
years, not the standard 5
degrees which most models
currently predict.

35. Causes ~ Global Dimming
Climatologists are stressing that the
roots of both global dimming causing
pollutants and global warming causing
greenhouse gases have to be dealt with
together and soon.
We are running out of time.