D4.3 - positive feedback cycles in global warming (1b)

Question 1

positive feedback

Answer 1

a process where the outcome of an action causes more of that action to occur, intensifying the response

Question 2

how can the release of carbon dioxide from the ocean cause a positive feedback loop?

Answer 2

• carbon dioxide is released from the deep ocean, moving into the atmosphere
• increased concentration of carbon dioxide traps more infrared radiation in the enhanced greenhouse effect
• oceans absorb heat trapped in the atmosphere
• carbon dioxide is less soluble in warm water
• the cycle repeats again

Question 3

how can an increase in the absorption of solar radiation cause a positive feedback loop?

Answer 3

• less reflection and more absorption of solar radiation
• warmer surface of the earth
• more snow and ice melts
• the cycle repeats again

Question 4

how can the melting of permafrost cause a positive feedback loop?

Answer 4

• more permafrost melts
• trapped methane is released, moving into the atmosphere
• increased concentration of methane traps more infrared radiation in the enhanced greenhouse effect
• warmer surface temperature of earth
• the cycle repeats again

Question 5

how can the decomposition of undecomposed organic matter in permafrost cause a positive feedback loop?

Answer 5

• warmer temperature of earth’s surface
• faster rate of enzyme reactions by decomposers within the permafrost, including decomposition of peat and previously undecomposed organic matter
• more carbon dioxide (from respiration) and methane released into the atmosphere
• increased concentration of carbon dioxide and methane traps more infrared radiation in the enhanced greenhouse effect
• the cycle repeats again

Question 6

how does peat form?

Answer 6

peat forms when organic matter is not fully decomposed because of acidic and anaerobic conditions in waterlogged soils

Question 7

how is methane produced?

Answer 7

• methane is produced from organic matter in anaerobic conditions by methanogenic archaeans
• some diffuses into the atmosphere, but most of it accumulates in the ground

Question 8

how can droughts and fires cause a positive feedback loop?

Answer 8

• warmer temperatures increase the risk of droughts and wildfires
• as trees and other plant matter burn, carbon dioxide is released into the atmosphere
• increased concentration of carbon dioxide traps more infrared radiation in the enhanced greenhouse effect
• the cycle repeats again

Question 9

what is net carbon accumulation?

Answer 9

indicates that in the overall process of carbon being released and stored, more carbon is being absorbed than released

Question 10

what is legacy carbon combustion?

Answer 10

combustion of undecomposed organic matter releases carbon stored from many thousands of years ago

Question 11

what is the impact of climate change on boreal forests?

Answer 11

climate change may cause boreal forests to reach a tipping point where less carbon dioxide is absorbed than is released, initiating a positive feedback cycle

Question 12

how did boreal forests show net carbon accumulation?

Answer 12

boreal forests have shown net carbon accumulation as they absorb more carbon dioxide from the atmosphere during photosynthesis, storing the carbon in biological molecules, than they release in respiration

Question 13

why are boreal forests becoming lesser net carbon accumulators?

Answer 13

warmer temperatures and decreased winter snowfall

Question 14

what has caused increased carbon loss in boreal forests?

Answer 14

increased frequency and intensity of forest fires
- combustion of trees releases carbon that was stored in biological molecules
- combustion of undecomposed organic matter in the soil releases carbon that was stored many thousands of years ago

Question 15

what has caused a decrease in carbon accumulation in boreal forests?

Answer 15

decreased carbon dioxide absorption
- a lack of water, due to reduced snowmelt, reduces photosynthesis and primary production to form biomass
- prolonged droughts leads to forest browning, where needles lose chlorophyll and drop off, limiting photosynthesis as light energy cannot be absorbed

Question 16

why would boreal forests becoming net losers of carbon initiate positive feedback cycles?

Answer 16

• increased carbon dioxide concentration in the atmosphere would increase the enhanced greenhouse effect
• this increases the frequency of droughts and wildfires, tipping the balance even further towards net carbon loss

Question 17

what is the process of nutrient upwelling?

Answer 17

1. trade winds blow east to west near the equator
2. surface water forms currents which moves towards the poles
3. cool, nutrient rich water from the bottom of the ocean moves upwards to replace the warmer surface water

Question 18

how does nutrient upwelling occur?

Answer 18

ocean currents are caused by wind moving water, and this can result in the upwelling of nutrient-rich water from the deeper ocean

Question 19

where are the nutrients in nutrient up-welling used?

Answer 19

phytoplankton use nutrients to produce biological molecules to build biomass to start marine food chains, in a process called primary production

Question 20

how does nutrient upwelling impact fish populations?

Answer 20

• phytoplankton are producers in marine food chains
• more nutrients means more phytoplankton biomass, and more energy flows to higher trophic levels, supporting a larger population
• fish populations would increase

Question 21

how can changes in the wind affect nutrient upwelling?

Answer 21

changes in the wind, and ocean currents, alter the timing and extent of nutrient upwelling

Question 22

how can nutrient upwelling changes occur naturally?

Answer 22

this can occur naturally when an ‘El Nino’ event occurs, where winds move from each shore and create an upward movement, preventing nutrient upwelling

Question 23

how can climate change affect nutrient upwelling?

Answer 23

climate change can impact nutrient upwelling
- warmer surface water can prevent nutrient upwelling to the surface, decreasing primary production and energy flow through marine food chains
- it can also increase intensity and frequency of El Nino events

Question 24

how would El Nino events affect fish populations?

Answer 24

• less nutrient upwelling means less biomass and energy is passed from phytoplankton along marine food chains
• fewer fish can be supported
• fish populations would decrease

Question 25

how has global warming caused species migration of montane birds in New Guinea?

Answer 25

Montane birds species live on Mount Karimui in New Guinea. Different species live on different elevations.
- global warming has caused birds to migrate to higher elevations (upslope range shift), where the temperature is lower at greater heights

Question 26

how has global warming caused species migration of temperate trees in North America?
how do the trees migrate?

Answer 26

Temperate species live in habitats with mild temperatures, with the seeds and saplings not being able to tolerate the cold.
- global warming has caused tree species to spread northward, where the temperature is lower near the poles
- trees migrate by spreading seeds in all directions, but successful germination may only occur if they have moved in a specific direction