This is was a simple presentation task assigned in a B.Sc. civil engineering course of AUST. Different information and necessary pictures from different sites were included and combined presentation slide was formed on topic of "Global Warming and Its reasons:Man made or otherwise". This slide is only for study purpose and a sample one on how to make a similar slide regarding global warming highlighting other reasons.

1. True Underlying Reason Behind Global Warming and Climate
Change: Anthropogenic or Beyond
Who is Responsible?
We humans? Or the nature itse
Or Both…

2. Team
• 1st Speaker:-17.02.03.030(IshtiqaueAhmed)
• 2ndSpeaker:-17.02.03.090( MarufAhmed)
• 3rd Speaker:-17.02.03.038(Md.SalehNoorShowrov)
• 4th Speaker:-17.02.03.130( KalyanDebnath)
• 5th Speaker:-15.02.03.106(Md.Aslammahmud).

3. Our stance in reasoning
• Some anomalies fact hints towards non-anthropogenic factors regarding
affecting the Climate Change and Global Warming and we think there are
other reasons from nature affecting it.
• As for example, such facts are-
• 1)Medieval Warm Period:-The Medieval Climate optimum or the Medieval Climate Anomaly
was a time of warm climate in the North Atlantic Region that lasted from 950 C.E. to 1250
C.E. and other regions got colder meanwhile such as the TROPICAL PACIFIC. Average global
mean temperatures of that time have been calculated to be similar to that of the early-mid-
20th century warming. Industrial revolution was not noticed like today’s one.
• 2)Extinction of Maya Civilization:-Delivering the Gordon R. Willey lecture, Turner detailed
evidence that two major droughts resulted in the decline and depopulation of that
civilization which happened roughly between 850 and 1000 A.D. At that time Earth was
comparatively warmer.
• 3) There was not much burning of fossil fuels 1000 years ago while it was still global warming
then.

4. These facts at least hints
that there are other causes
behind the Global Warming
and Climate Change.

5. • 2nd speaker:
• Maruf Ahmed(17.02.03.090)

6. Global Warming and Climate Change
Terms and Causes
And, Climate change is a
long-term change in the
average weather patterns
that have come to define
Earth's local, regional and
global climates.
Global warming is a gradual
increase in the earth's
temperature generally due to the
greenhouse effect caused by
increased levels of carbon
dioxide, CFCs, and other
pollutants or due to natural
causes.

7. Causes
• Anthropogenic Causes Of
Climate change
1. Oil and Gas. Oil and Gas is used
all the time in almost every
industry.
2. Deforestation. Deforestation is
the clearance of woodland and
forest, this is either done for the
wood or to create space for farms
or ranches.
3. Waste.
4. Power Plants.
5. Oil Drilling.
6. Transport and Vehicles.
7. Consumerism.
8. Farming.
9. Industrialization.
10. Overfishing.

8. Major Greenhouses Gases are
• Caron-dioxide(mainly)
• Methane:- Concentrations nearly doubled in the last years.
• CFC:- Heat absorption and trapping capability ranges from hundreds
totimes more than carbon dioxide.
• Highly stable compound, so even if production stops at current level, their
effect is expected to linger at least another century
• Nitrous Oxide:-
• agricultural application of fertilizer and fossil fuel burning.
• Stable compound, so effect will persist for several decades even if
production is completely stopped.
• Water vapor-High heat storing capacity.

9. Why Carbon dioxide is mainly responsible for Global
Warming as Greenhouse Gas-
• Carbon dioxide molecules in the atmosphere absorb long-wavelength
infrared energy (heat) from the Earth and then re-radiate it, some of it
back downward. Oxygen and nitrogen don’t interfere with infrared
waves in the atmosphere. As CO2 soaks up this infrared energy, it
vibrates and re-emits the infrared energy back in all directions. About
half of that energy goes out into space, and about half of it returns to
Earth as heat, contributing to the ‘greenhouse effect.’

10. • 3rd Speaker:
• Md. Saleh Noor Showrov(17.02.03.038)

11. Natural Factors Behind Global Warming and
Climate Change

12. 1)Earth’s own Feedback Loops

13. 1)Earth’s own Feedback Loops
• a)Positive Feedback Loop:- it will
accelerate a response, making the
climate much warmer or colder. For
example:- water vapor feedback loop.
• -
b)Negative Feedback Loop:- it will self-regulate to
create stability within the system. For example:-
Solubility pump of the ocean.

14. 2)Milankovitch Cycles

15. 3)Atmospheric Transparency
• Dust and Aerosols absorbs light, cooling the
atmosphere. Aerosols can influence the Earth's climate in
two ways. When the sky is clear (devoid of clouds),
aerosols can reflect incoming sunlight back to outer space
– the direct effect. This blocks part of the energy that would
have reached the surface, thus having a cool effect on the
climate.

16. 4)Roughness of the Earth’Surface
• Laminar Air flow smoothly over smooth earth
surface but causes friction with rough surface
because of which kinetic energy is given off as
heat. Vegetations around earth surface also act
as rough objects to cause friction

17. 5)Albedo Effect
• Light surfaces reflect more heat than dark surfaces. This is called the albedo effect.
Albedo is an expression of the ability of surfaces to reflect sunlight (heat from the
sun).
• When the Earth's temperature dropped because of its position in orbit around the
Sun, and the tilt of the axis, the ice sheets grew. This in turn caused more heat to be
reflected and the ice. Albedo is one of the major properties that controls how much
energy is absorbed by the surface of the Earth, the cloudiness and ground cover are
important factors in climate models. sheets to expand further.
• Darker colored vegetation lead to Global Warming while lighter colored vegetation
lead to cooling.
• For Example: Grass in a meadow will reflect between 25 – 30% of energy.

18. 6)Ocean Conveyor Belt
• The global ocean conveyor belt is a constantly moving system of deep-
ocean circulation driven by temperature and salinitycharacterized by strong
northward movement of upper warm waters of the gulf stream in the Atlantic
ocean. The process goes on as shown:
Ocean currents appears to be related
to water temperature, air pressure,
storms, weather over periods around a
single upto decades And effect can be
upto 10 times stronger than
observed in the past century, and
larger, over a
period of a few decades.

19. 7)El nino effect
Wind move the surface water away from the shore, cold water rises with nutrients,
which in turn promotes growth of algae resulting in growing fish population
leading to growing bird population.
Occurs in seven yearly cycles
• Ocean water becomes warmer
• Upwelling stops, nutrient can’t rise
• Poor algae growth poor fish population
sea birds leave or die
• High rainfall and flooding in Peru
• Droughts and fires become common in
Australia and Indonesia
• Warm ocean water provides an atmospheric
heat source, so El Nino changes global
atmospheric circulation.

20. • 4th Speaker:
• Kalyan Debnath(17.02.03.130)

21. Effects of Climate Change
 rising maximum temperatures.
 rising minimum temperatures.
 rising sea levels.
 higher ocean temperatures.
 an increase in heavy precipitation (heavy rain and hail)
 shrinking glaciers.
 thawing permafrost.

22. Effects of Global Warming
• More frequent and severe weather.
• Higher temperatures are worsening many types of disasters, including
storms, heat waves, floods, and droughts.
• Higher death rates.
• Dirtier air.
• Higher wildlife extinction rates.
• More acidic oceans.
• Higher sea levels due to ice cap melting being overall accelerated.

23. Effects from Sea level Rise
This will threaten people living in the coastal Regions mostly. Erosion of
beaches, making structure more vulnerable to damage from waves will occur.
This leads to further expense as investment costs for dams, dikes are to be
constructed to protect structures.
Groundwater supplies for coastal
communities are also threatened due to
Coastal erosion and rise in sea level, increased
hydrostatic pressure of sea water table,
manages to cause saltwater intrusion in ground
aquifer freshwater tables.

24. Ways to mitigate these changes
• There is nothing human beings can do control the
natural factors behind Global Warming and Climate
Changes.
• However anthropogenic causes(global warming) are
expected to be doubling the rate of these changes. So
as human beings contributing to save life forms and
normal habitat for living beings, we can take measures
reducing and controlling the man made factors behind
Global Warming and Climate Change at least.

25. Our ways tto reduce these changes:-

26. • 5th Speaker:
• Md. Aslam Mahmud(15.02.03.106)

27. Coming to Conclusion
• We always blame Greenhouse gas emission such as
CO2 from man made sources as those are directly visible
to us. CO2 can not be removed from earth and it is a
compulsory requirement for photosynthesis biological
reaction in plants which is providing the must element
oxygen for our survival.
• Though scientist and some long old facts indicates
existence of other facts behind Global Warming and
Climate Change, basing on these facts we can not only
blame anthropogenic reasons.

28. References:-
https://en.wikipedia.org/wiki/Medieval_Warm_Period
• https://news.harvard.edu/gazette/story/2020/02/new-clues-about-how-and-why-the-maya-culture-collapsed/
• https://byjus.com/biology/global-warming/
• https://sciencing.com/5-causes-global-warming-8232444.html
• https://news.climate.columbia.edu/2021/02/25/carbon-dioxide-cause-global-warming/
• https://sustainabilitymag.com/top10/top-10-causes-global-warming
• https://www.iea.org/reports/multiple-benefits-of-energy-efficiency/emissions-savings
• https://climateatlas.ca/why-climates-change
• https://gml.noaa.gov/outreach/info_activities/pdfs/TBI_understanding_feedback_loops.pdf
• Albedo Effect: https://www.npolar.no/en/fact/albedo/
• https://energyeducation.ca/encyclopedia/Albedo
• https://aspirantforum.com/2020/11/22/effect-of-albedo-on-global-warming/
• https://www.essearth.com/why-albedo-is-important-for-our-melting-ice-caps/
• Milankovitch cycle not responsible for climate change: https://climate.nasa.gov/ask-nasa-climate/2949/why-milankovitch-orbital-
cycles-cant-explain-earths-current-warming/
• https://slideplayer.com/slide/7881776/
• https://www.gfdl.noaa.gov/aerosols-and-climate/
• https://phys.org/news/2016-04-nasa-global-earth.html
• https://www.eesi.org/topics/geothermal/description
• https://www.nrdc.org/stories/are-effects-global-warming-really-bad