Lecture iii - Anthropogenic causes of climate change

Question 1

Describe natural greenhouse effect

Answer 1

• naturally occurring ghg eg CO2, CH4, nitrous oxides help keep earth warm (maintain avg 15 C)
• w/o natural ghg, avg temp wld b freezing -18 C

Question 2

Why is present day climate becoming a concern?

Answer 2

-earth is in stage of rapid warming
- rate of increase of surface temp bcome more rapid/ has accelerated, rising on average
- called global warming/contemporary CC

Question 3

Human-induced global warming of … deg C has…

Answer 3

1.1°C

spurred changes to earth’s climate, unprecedented in recent human history

Question 4

Name characteristics of global warming

Answer 4

• characteristics changing include temp, precipitat n, snow cover & extreme weather events
• droughts bcome more severe (intense) & frequent in some areas
• rivers melt earlier in spring
• ice sheets (Greenland & Antartic) melt earlier in spring
  => extreme flooding events (high magnitude, higher frequency)

Question 5

Explain enhanced greenhouse effect

Answer 5

• ghg effect oni a problem when there r excessive ghg in troposphere, enhancing ghg effect, raising mean annual temp of world
• Since 1750s which saw start of IR, man’s intense activities hv accelerated increase of ghg act as thermal blanket re-radiating heat back into earth’s atmos
• CO2 is principal ghg, provides main warming/ ‘radiative forcing effect’
• CO2 & other ghg once emitted, can stay in atmos for long time; even if emissions stop today, warming will continue (thermal inertia)
• bringing anthropogenic carbon emissions to zero WON’T reduce global avg temp NOW - effect oni can b felt years later (in long term)

Question 6

Define anthropocene

Answer 6

idea that humans hv create its own ‘epoch’ beginning when human activities started to hv a significant global impact on earth’s geology & ecosystems

Question 7

How has atmospheric CO2 concentration changed from pre-industrial times?

Answer 7

pre-industrial: 270ppm (b4 1750s)

by 1950s, rose to 310ppm

2022 - abt 418ppm

Question 8

What can be said about the rapid increase in CO2 levels in the last few centuries?

Answer 8

• argued that human activities since IR ard 1750 hv increased atmospheric trace gases eg CO2
• human-induced CO2 emissions enhanced edi existing gh effect, causing global warming & fundamental change in climate
  => enhanced gh effect

Question 9

What are two main ways in which anthropogenic activities have contributed to global warming

Answer 9

1. Increase in emissions of ghg (CO2, CH4, etc.) arising fr human activity
   a. Industrial
   (burn fossil fuel in intense manufacture gds, transport, etc.)
   b. Agricultural
   ( change in landuse eg livestock rearing)
   c. Domestic
   (indiscriminate waste disposal, use transport, natural gas piping, etc.)
2. Reduct n of carbon sink
   a. large scale, accelerated deforesta n
   b. warming, acidifi n of oceans

Question 10

Explain how industrial activities increase greenhouse gas emissions

Answer 10

• produce gds, raw materials we use everyday (intense manufacturing activities)
• emit large qtys of ghg eg CO2, nitrous oxides, etc.
• emissions can be either direct or indirect

Question 11

Explain how agricultural activities increase greenhouse gas emissions

Answer 11

• reduce forests (carbon sinks) that absorb CO2 -> more CO2 thus trapped in atmos, re-emit longwave rad n back to earth, warming it
• use of fertilisers, tilling, increase nitrous oxides in atmos
• livestock rearing eg cattle ranching produce methane when they belch as part of their digest n

Question 12

Explain how domestic activities increase emission of greenhouse gases

Answer 12

• eg transport, cook, dispose/recycle waste, refrigerat n, electricity consumpt n
• transport n: cars trucks, ships, trains, planes
• CO2 emission fr combust n of petroleum-based products
• likely increase as we bcome more dvloped (w associated increased affluence) & demand for more energy
• Growing pop n Pa = growing global demand for more gds, svcs to b produced
• Increased affluence = higher PP
  => can demand, pay for more gds, svcs
• Dietary preferences/ lifestyle
  -> prefer meat-based foods

Question 13

Explain reduction of carbon sinks by deforestation

Answer 13

(release of stored carbon)
- deforestat n is generally categorised as long-term/permanent removal of forest cover & convers n to other land uses (non-forested land)
- if not properly managed, can cause permanent destruct n & eventual disappearance of once renewable resource
- Large scale deforestat n increased rapidly in last 50 yr
eg Amazon rainforest (holds 20% of all CO2 in atmos), Congo Basin Rainforest
BUT, rapidly being cleared for agriculture & urban dvlopmt
=> release carbon stored in trees back into atmos
- farming activities may oso increase release of CO2 & CH4 by animals

Question 14

What are main anthropogenic causes of tropical deforestation

Answer 14

1. Logging (for timber & urban expan n)
2. Livestock ranching eg cattle ranching
3. Agricultural expan n eg palm oil
4. Firewood/fuelwood collect n (for subsistence farmers)
5. Urban dvlopmt (to accommodate growing global pop n )
6. Mining for resources

(all these human activities are the reason rainforests r disappearing)

Question 15

Elaborate on primary losses in tropical rainforests

Answer 15

• 3 countries account for ~ 48% of primary rainforests loss in 2018

1. Amazon forest in Brazil (1.3ha lost)
   cleared for cattle ranching and timber logging
2. Africa’s congo rainforest loss due to
   - conversion to agricultural lands, timber exports, increased pop n demand for firewood
3. Indonesia rainforests (300Kha lost)
   - cut down to make way for palm oil plantat n (palm oil used in shampoos, cleaning pdt, detergents, lotions, lipsticks, etc.)

Question 16

Explain cattle ranching as a cause of tropical deforestation

Answer 16

• ranching is farming, raising of livestock to produce meat for food product n
• rise in fast food chains, change in dietry needs (prefer meat) & increasing affluence
  eg large amt beef fr cattle in Amazon greatly demanded by burger chains eg Burger King, McDo, etc.

Question 17

Explain agricultural expansion as cause of tropical deforestation

Answer 17

• globally, large scale commercial agri (cash crops = cultivate for profit) is main cause of deforestat n (up to 75%)
• In Latin America, deforestat n related to large-scale ranching (beef) & oso soybean product n (large part of GDP for many Latin America countries)
• In SEA (esp Indonesia), deforestat n related to palm oil agri (palm oil plant n now cover > 27million ha - forests & human settlemt destroyed & replaced by ‘green deserts’ w no biodiversity on area size of New Zealand)
• In Africa, expan n of small-scale shifting agri (slash-and-burn cultivat n) cause deforestat n

Question 18

Explain urban expansion as cause of tropical deforestation

Answer 18

• increasing pop n & increased affluence will increase demand for land, other forest pdt eg timber, cattle, agricultural produce, etc.
  => all these increased demands cause accelerated rate of deforestat n
  eg In SG, compared to 1800, oni 2.99% of primary forest remains

Question 19

What are underlying drivers of deforestation?

Answer 19

• rapid pop n growth (global)
• econ dvlopmt -> capitalism (increased affluence causing higher PP & increasing demands)
• urban n (global)
• poverty (in LDCs)
• Low agri productivity (poor qlty of land)
• unequal distribut n of land

Question 20

Explain reduction of carbon sinks ( oceans)

Answer 20

• ocean is planet’s greatest C sink (vital buffer against impacts of CC, stabilises climate)
• absorbs 30% of all CO2 emiss n, capture 90 % of excess heat generated by these gas emiss n trapped in earth’s system
• oceans absorb C 20 times more than trees by:
  i. photosynthesis of phytoplankton
  ii. atmos CO2 dissolving in ocean, esp cold waters

HOWEVER, more ghg emiss n affected ocean health
- human activiteis eg burn FF cause more ghg emis n, cause increase global temp
- as global temp increase, more atmos CO2 dissolved in ocean sink, increase pH lvl (more acidic) - 30% more acidic than pre-industrial period
- warming & acidifying of seawater reduce ocean ability to absorb CO2
- when ocean warm up, ocean C capacity decrease
- more CO2 released into atmos

Question 21

How does ocean acidification harm ecosystems?

Answer 21

• ocean acidifi n can create condit n that eat away minerals used for calcificat n by oysters, clams, lobsters, shrimp, coral reefs, other marine life to build shells, skeletons
• dissolved CO2 in ocean bcome carbonic acid which react w calcium ion to form bicarbonate, making calcificat n of organisms less available
  => damaging effects to aquatic (lack of nutrients) & terrestrial ecosystems