Climate Change (DP IB Biology)

Positive feedback is a mechanism that leads to increased change away from a normal state.

Global warming is an example of a positive feedback cycle because global warming causes changes that lead to more global warming.

False.

Melting polar ice caps decrease Earth's albedo, leading to more absorption of solar energy.

Wildfires contribute to the positive feedback cycle of global warming as follows:

• atmospheric carbon dioxide is increased during wildfires due to combustion of plant material and reduced photosynthesis

• global warming increases

• wildfires become more likely to to higher temperatures

False.

Peat bogs only release carbon dioxide when decomposition increases due to warming. When stable they function as carbon sinks.

The connection between increased activity of microorganisms and increased global warming is as follows:

• increased decomposition in peat bogs and permafrost releases carbon dioxide as temperatures increase

• increased activity of methanogenic microorganisms releases methane as permafrost melts

False.

Boreal forests can switch from being carbon sinks to carbon sources; this tipping point occurs due to the effects of global warming.

The primary cause of reduced water availability in boreal forests due to global warming is reduced snowfall due to increased temperatures; this reduces the water available from snow melt.

Forest browning is the process during which trees lose their green pigment and turn brown due to drought caused by global warming.

Legacy carbon combustion is the release of carbon that has been locked up for many years in living trees, dead needles on the ground, and within the soil itself, typically through forest fires.

Global warming affects emperor penguins by causing earlier melting of sea ice; this reduces the time that Emperor penguins have to raise their young on the Antarctic sea ice where they breed.

The early loss of Arctic sea ice forces walrus mothers to care for their young further from the water's edge, leaving young without protection for longer periods when the mothers hunt for food.

Changes to ocean currents due to global warming can prevent normal nutrient upwellings from the deep ocean. This reduces primary production and means that less energy is available to marine food chains.

Global warming has caused many bird species in the mountains of New Guinea to migrate to higher altitudes; this is an upslope range shift.

Global warming has caused range contraction and northward, or poleward, range shifts in North American tree species.

Ocean acidification is the process by which ocean pH decreases. This occurs when there is an increased in dissolved carbon dioxide, leading to an increase in H⁺ ions.

Ocean acidification can weaken and dissolve the calcium carbonate exoskeletons of corals and reduce the availability of carbonate ions needed for building these structures.

False.

While ocean acidification and global warming share the same cause (increased atmospheric carbon dioxide), ocean acidification is not a direct result of global warming.

Coral bleaching occurs when coral polyps expel their algae symbionts due to high water temperatures, causing reefs to lose their bright colours.

Coral bleaching can result in death of coral polyps and the collapse of reef ecosystems.

Carbon sequestration is the process of capturing and storing carbon dioxide from the atmosphere.

Reforestation involves planting trees in deforested areas while afforestation is the creation of new forests on lands that have not been recently forested.

Peat bogs can be restored by:

• filling in drainage ditches to restore peat to its waterlogged state

• reducing the harvesting of peat to allow recovery

The two approaches to carbon sequestration debated by scientists are:

• planting non-native tree species that grow quickly and sequester carbon rapidly

• rewilding with native species; this sequesters carbon more slowly but may benefit biodiversity

Phenology is the study of the timing of biological events.

Environmental factors that can influence the timing of biological events include:

• photoperiod (day length)

• temperature

There are other relevant factors, for example water availability, but these are the two covered by the IB HL syllabus.

True.

The timing of plant flowering can be influenced by day length.

False.

Birds may not always build their nest on the same date each year. The timing of nesting will be determined by factors such as temperature and food availability.

Climate change is causing a phenological mismatch between migrating reindeer and the growth of their food plant, Arctic mouse-ear chickweed.

• Reindeer migration timing is determined by day length, while the growth of Arctic mouse-ear chickweed is determined by temperature

• This means that migration timing is unaffected by climate change, but the growth of Arctic mouse-ear chickweed is, resulting in low food availability for reindeer during their breeding season

The graph shows that climate change has caused hatching date in great tits to move earlier by one week, but the peak of food availability to move earlier by two weeks. This means that the timing of peak food need of the great tits does not match with peak food availability.

Global warming has increased the number of life cycles completed by the spruce bark beetle each year; higher temperatures mean that two life cycles are more likely to occur. This increases the size of the beetle population and therefore increases their impact on tree growth.

Climate change has resulted in an increase in fitness for the brown tawny owl variant. It is thought that a reduction in snow cover provides brown owls with a reproductive advantage over pale-coloured owls due to increased camouflage.