IB Biology D4.3: Climate change worked solutions

Greenhouse gases absorb the long-wave (infrared) radiation that the warmed surface emits and re-emit some of it towards the surface, so heat is retained (A). They do not reflect sunlight (B), do not convert wavelengths (C), and the ozone layer is a different issue (D).

Wind turbines supply energy without burning fossil fuel, so less \ce{CO2} is released (A). Draining peat, clearing forest and burning waste all release carbon or remove uptake.

Peat needs waterlogged soil with little oxygen and acidity, so decomposers are inhibited and dead plant matter stays partly decomposed (B). Oxygen-rich, drained or alkaline conditions allow decomposition.

In B the effect of melting (darker surface, more absorption) strengthens the warming that caused it, so it is positive feedback. A and D reduce warming (negative feedback) and C is a consequence with no return to warming.

A stable warm layer mixes poorly with the cold, nutrient-rich water below, so less upwelling brings fewer nutrients to the surface and phytoplankton production falls (B).

As the climate warms the temperature zone that suits the species shifts upslope, so both limits rise (A). The other options do not follow from the data.

Prolonged warm water stresses the coral, which expels its zooxanthellae. The coral then lacks the algae and turns white (A).

Phenology concerns the timing of seasonal events, such as leaf opening (B). Range shift, colour change and shell thickness are not timing.

(a) Increase =5.6-4.0=1.6 Gt (1); 1.6/4.0\times100=40\% (1). (b) The changes are 0.4, 0.8 and 0.4 Gt, so 2000 to 2010 (1).

(a) Any three: burning releases carbon dioxide, a greenhouse gas (1); short-wave radiation from the Sun reaches the surface and the surface emits long-wave radiation (1); carbon dioxide absorbs this long-wave radiation (1); it re-emits some of it back towards the surface, so heat is retained and the temperature rises (1).

(a) Any four: fossil fuel combustion releases carbon dioxide (1); carbon dioxide is a greenhouse gas whose concentration therefore rises (1); short-wave radiation from the Sun passes through the atmosphere and warms the surface (1); the surface emits long-wave (infrared) radiation (1); the extra gas absorbs more of this long-wave radiation (1); it re-emits some towards the surface, so more heat is retained (1); the enhanced greenhouse effect raises temperature (1).

(a) The soil is waterlogged, so there is little oxygen (1); the conditions are acidic, so decomposers are inhibited (1); dead plant matter is only partly decomposed and accumulates slowly over thousands of years (1). (b) Draining lets air into the soil (1); decomposers respire aerobically and the stored carbon is released as carbon dioxide (1).

(a) Warming thaws the permafrost (1); decomposers break down the organic matter that was frozen (1); methane and carbon dioxide are released, strengthening the greenhouse effect and warming further (1). (b) The extra growth removes carbon dioxide, which opposes the warming (1). (c) Loss of ice and snow, so less sunlight is reflected; or warmer oceans releasing carbon dioxide; or drought and fire (1).

(a) Warm water is lighter, so a stable layer forms and mixes less with deeper water (1); less nutrient-rich water is brought to the surface (upwelling) (1); phytoplankton growth and primary production fall (1). (b) Any named consumer, for example a seabird (1) with less food, so lower breeding success or condition (1).

(a) Any six linked points: burning fossil fuels releases \ce{CO2} (1); deforestation removes uptake and livestock and rice release \ce{CH4} (1); these gases absorb long-wave radiation and retain heat, strengthening the greenhouse effect (1); ice and snow melt, so less sunlight is reflected (1); oceans warm and absorb \ce{CO2}, so coral reefs bleach and calcify less (1); species shift towards the poles and uphill (1); drought and fire release more carbon (1); permafrost thaws and releases methane (1).

(a) Shifts are 120, 90, 130, 30, 140 m (1); mean =510/5=102 m (1). (b) All species have moved to a higher altitude, by between 30 and 140 m (1). (c) Any two: species from lower down compete with or prey on the residents; the area at higher altitude is smaller, so populations shrink; species with specialised needs decline; food-web relationships change (2). (d) It cannot move higher, so its habitat shrinks and it may go extinct (1).

(a) As carbon dioxide rises, calcification falls (1). (b) Change =6.5-12.5=-6.0 (1); 6.0/12.5\times100=48\% decrease (1). (c) The 400 \muatm tank, the present-day level; any one of temperature, light, salinity, species present (1). (d) The ranges 9.5 to 10.5 and 5.8 to 7.2 do not overlap, so the difference is likely to be real (1). (e) Carbon dioxide dissolves in seawater and lowers its pH, so there are fewer carbonate ions (1); corals need carbonate to build calcium carbonate skeletons, so calcification slows (1).

(a) Growth increases as temperature rises (positive correlation) (1). (b) 20\,{}^\circC (1). (c) Y grows faster at 25 than at 10 (0.34 against 0.25), but X does not keep rising: it peaks at 20 and falls to 0.30 (1); the hypothesis is supported for Y at the end points only and is not supported for X above 20\,{}^\circC, so overall it is not supported (1). (d) Growth rate of X falls (from 0.45 to 0.30 mm d^{-1}) (1).

(a) As ice extent falls from 18.5 to 13.1 million km^2 (1), chicks fledged fall from 72 to 38 per 100 pairs: a positive correlation (1). (b) 38-72=-34 (1); 34/72\times100=47\% decrease (1). (c) Any two: breeding sites on landfast ice are lost or break out early; the ice-algae base of the food chain is reduced, so less food; chicks fall into the water or are not fledged by the time ice breaks (2). (d) A correlation does not show cause, and other factors such as food supply or predators may also have changed over the five winters (1).

(a) The warmer the April, the earlier the caterpillar peak (negative correlation with date) (1). (b) At 6.0: 150-146=4 days, the peak comes after hatching (1); at 9.0: 146-131=15 days, the peak comes before hatching (1). (c) The chicks hatch after the peak of food, so there is less food and fewer survive (1); birds that lay earlier match the new peak, leave more offspring, and the early-laying allele becomes more frequent (1).

(a) The balance falls steadily from a net gain of 45 to a net loss of 25 (1); change =-25-45=-70 g C m^{-2} yr^{-1} (1). (b) Less snow means less meltwater stored for summer, so drought stress increases (1); trees close stomata or die back, so photosynthesis and primary production fall (1). (c) Burned area rose from 0.8 to 3.2 % (four times) (1); severe fires burn into the soil organic layer and release legacy carbon stored for decades, so release exceeds the reduced uptake (1). (d) Beyond the point where release exceeds uptake the forest adds \ce{CO2} to the air (1); that warms the climate further, causing more drought and fire: a positive feedback that is hard to reverse (1).

(a) Today: 700/(13.0-7)=116.7 days per generation (1); 140/116.7=1.2, so 1 whole generation (1). 2050: 700/(17.5-7)=66.7 days; 140/66.7=2.1, so 2 generations (1). (b) Today \times20; in 2050 20^2=\times400 (1); 20 times as many beetles at the end of the year (1). (c) More spruce are attacked and killed (1); dead trees stop sequestering carbon and decompose or burn, releasing carbon, which adds to warming (1).

(a) 0.71-0.58=0.13 (1). (b) In long snow winters grey owls survive better (0.71 against 0.58) and in short snow winters brown survive better (0.69 against 0.60) (1); the variant that matches the background is detected less by predators or prey (camouflage) (1); survival differences mean the favoured variant leaves more offspring, so each winter type selects for a different variant (1). (c) Short-snow winters become more common, so brown survives and breeds more (1); the frequency of the brown allele rises across generations: climate change drives evolution (1).

(a) A long-term rise (1) with a regular yearly cycle of about 6 ppm (1). (b) 414-390=24 (1); 24/390\times100=6.2\% (1). (c) In the summer growing season of the northern hemisphere, land plants take up more carbon dioxide in photosynthesis than they release, so concentration falls (1); in winter respiration and decay exceed uptake, so concentration rises (1). (d) The graph contains no temperature data, so it cannot show a link to warming (1); even with temperature data, a correlation alone does not prove cause: the mechanism (absorption of long-wave radiation) and other evidence are needed (1).

(a) Warming: 1.1 against 2.0 with no overlap of error ranges, while at 26 ^\circC pH made little difference (1.9 against 2.0) (1). (b) 0.40-1.00=-0.60 (1); 0.60/1.00\times100=60\% decrease (1). (c) Warming lowers algae density (bleaching), so less food is supplied and calcification falls a little (0.85) (1); acidity lowers calcification (0.62) without changing algae, so the effect is on skeleton building through a lower carbonate ion concentration (1); together the effects add up, giving the lowest values (1). (d) Coral cover declines and the skeleton structure erodes (1); habitat is lost, so the species that depend on it decline (1).

(a) Normal NPP =24-11=13; drought NPP =19-10=9 (1). Normal balance =13-(10.5+1.0)=+1.5 (1); drought balance =9-(10.5+3.0)=-4.5 t C ha^{-1} yr^{-1} (1). (b) Drought lowers photosynthesis, so NPP falls (1); fire release rises while decomposers keep releasing carbon, so release exceeds uptake and the plot is a source (1); the extra \ce{CO2} adds to warming, which makes drought and fire more likely: positive feedback (1). (c) In a rewetted peatland the water excludes oxygen, so decomposers are inhibited and carbon accumulates (1) whereas in the forest plot aerobic decomposers continue to release carbon each year (1).

(a) Cover after bleaching =60-35=25\% (1); time =35/2.5=14 years (1). (b) In 6 years the reef gains 6\times2.5=15 points (1), but each event removes 35, so cover falls by 20 points each cycle and cannot return to 60% (1). (c) The community cannot return to its original state after disturbance: it has lost resilience (1); beyond a threshold the reef shifts to algae-dominated seabed, which is hard to reverse even if warming stops (1).

(a) Density has fallen at 1900 m (12.0 to 4.0) (1) and risen at 2100 and 2300 m (to 9.5 and 6.0), which is an upslope shift (1). (b) The newcomers compete with residents for light, water, nutrients or space (1); species with a lower competitive ability decline, so the community changes (1). (c) Quadrats placed randomly with the same number and area at each altitude and at the same time of year (1); the same method in 1990 and 2020 so the difference is due to climate and not to the method (1).