Question
Remote sensing satellites are used to monitor the Earth’s ecosystems. One measure of ecosystem status is leaf area index (LAI), which is the total area of leaves in square metres per square metre (\(m^2\) \(m^{-2}\)) of the Earth’s surface. The graph shows LAI estimates, calculated
using data from the Global Inventory Monitoring and Modelling System (GIMMS), during the period from 1981 to 2011. The data points are monthly averages in four latitudinal zones in the northern hemisphere
(a) Compare and contrast the LAI data for the arctic and temperate zones.
(b) Suggest reasons for the differences in LAI between the boreal and equatorial zones.
There is evidence of a change in mean LAI values on Earth over recent decades. Changes can be quantified by calculating LAI anomalies. These are differences between annual LAI values and the mean LAI for the entire given time period. The graph shows global LAI anomalies for the period from 1981 to 2014, based on data from GIMMS. It also shows mean global LAI anomalies between 1981 and 2009, based on data from three other remote sensing programmes. Vertical bars show the timing of El Niño events. The darkness of the bars indicates the intensity of the El Niño events. The darker the bar, the more intense the event.
(c) Analyse the data shown in the graph for evidence of a relationship between LAI and El Niño events.
(d) The data in the graph show a long-term trend in global LAI.
(i) State the trend.
(ii) Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide (\(CO_2\)) concentration could cause the observed change in LAI.
The 2015 Paris Agreement sets out an international framework for avoiding dangerous climate change. A key aspect is conserving and enhancing sinks of greenhouse gases, including forests. Free air carbon dioxide enrichment (FACE) experiments are being used to investigate whether increases in atmospheric \(CO_2\) concentration will cause biomass increases in existing forests. Three FACE experiments have been running for at least ten years in young, developing forests. Photosynthesis rates are measured in 25 to 30 m diameter plots. In control plots, carbon dioxide concentrations remain at current atmospheric levels (ambient \(CO_2\)). In treatment plots, the \(CO_2\) concentration is raised by 50% (elevated \(CO_2\)). The table gives some details of these experiments and the highest annual net primary production recorded during the period of the experiment. Net primary production is the mass of carbon absorbed and fixed by photosynthesis in plants that is not released due to plant respiration.
(e) State the effect of elevated \(CO_2\) on net primary production in these young, developing forests.
(f) Outline one benefit of conducting similar FACE experiments in multiple locations.
In each forest, there are two or three trial plots per \(CO_2\) treatment. The bar chart shows the allocation of carbon from net primary production to different parts of the trees in these trial plots.
(g) Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.
Answer/Explanation
Answer :
(a) Similarity
both rise to peak/maximum/are highest in summer/warmest
months/June/July/August
OR
both lowest in winter/December/January
OR
both rise then fall;
Difference
temperate always higher/higher overall/higher throughout year
OR
temperate peak is higher/is one month later/is in August versus July in arctic;
(b)
a. climate/temperature/light consistent throughout year in equatorial but seasonal variation in boreal;
b. conditions suitable for photosynthesis throughout the year in equatorial but not in boreal;
c. temperatures higher/growing season longer in equatorial versus lower/shorter in boreal;
d. water frozen/unavailable in boreal during winter whereas always available in equatorial;
e. shorter daylengths in winter in boreal (than those months in equatorial so lower LAI);
f. boreal LAI higher (than equatorial) in July due to longer daylengths;
g. equatorial trees/plants are evergreen / boreal trees/plants are deciduous/have less/no leaves in winter;
h. variation in angle of light rays (between different latitudes);
(c)
a. decreases in LAI during El Niño
OR
increases in LAI between El Niño events;
b. 1983-4/other example of a decrease during El Niño
OR
1984-6/other example of increase between El Niño events;
OR
94-95/2009 anomalous as LAI rises during El Niño event;
OR
99-2000 anomalous as LAI decreases between El Niño events;
c. larger decrease (in LAI) with more intense/longer El Niño events
OR
no/less decrease during less intense/briefer El Niño events;
(d)
i. Increase/increasing/upwards/rising (trend);
ii. a. more photosynthesis (with higher carbon dioxide concentration);
b. more plant growth/more (plant) biomass/more leaves/more plants;
(e)
increases it/higher (maximum annual net primary production);
(f)
check whether trend is confirmed/replicated/not specific to some forests
OR
investigate worldwide effects (of rising carbon dioxide)
OR
(check whether results are affected by) differences in tree species/types of
tree/soil types/rainfall/temperature/climate/latitudes/conditions/biome/ecosystem;
(g)
a. more carbon stored/allocated (by the tree as a whole) with elevated carbon dioxide;
b. evidence (from the bar chart) is strong (for the trend/hypothesis);
c. all elevated plots have more carbon stored than all ambient plots in all sites/no
overlap;
d. more/most carbon allocated to wood (in stems and roots) with elevated carbon
dioxide;
e. more carbon allocated to narrow roots/leaves with elevated carbon dioxide;
f. narrow roots increase most in Oak Ridge;
g. most increase in wood (in stems and roots) in Rhinelander and Duke;
h. much/more variation between plots at Oak Ridge (than at Rhinelander and
Duke);
i. no error bars so significance of differences is uncertain;
Question
The graphs show how the global mean surface temperature changed from 1978 to 2018, as well as the amount of energy reaching the surface of the Earth from the Sun.
(a) It has been argued that variation in the global mean surface temperature has been caused by variation in energy from the Sun. Analyse whether evidence from the graphs supports this argument.[2]
(b) Explain how increased levels of atmospheric carbon dioxide contribute to global warming. [3]
(c) State one other gas that contributes to global warming. [1]
Answer/Explanation
a (Evidence does not support this argument because:)
a. overall increase in surface temperature but no overall increase/slight decrease in solar irradiance;
b. peaks and troughs in solar irradiance do not correspond with fluctuations in surface temperature;
b a. carbon dioxide absorbs/traps long wavelength/infra-red radiation;
b. more heat trapped in/less heat escapes from atmosphere with more carbon dioxide;
c. short wave/UV radiation from the sun passes through the atmosphere/reaches the Earth’s surface;
d. radiation from the sun/sunlight warms the (surface of the) Earth;
e. long wavelength/infra-red radiated from the (warmed) Earth’s surface;
c methane/nitrous oxide/water vapour/ozone/CFCs/other halogenated gases;
Question
The map shows the widespread distribution of coral reef ecosystems (indicated by black dots) in the world’s oceans. Death of coral reefs is related to increasing atmospheric carbon dioxide concentrations.
Explain how increased atmospheric carbon dioxide concentrations can lead to coral death.
▶️Answer/Explanation
Markscheme
a. carbon dioxide dissolves in oceans/seawater ✔
b. carbonic acid formed/equation/lowers pH/makes water acidic ✔
c. prevents deposition of calcium carbonate/causes calcium carbonate to dissolve ✔
d. skeleton of (hard) corals degraded ✔
e. carbon dioxide is a greenhouse gas/causes warming/increases temperatures ✔
f. warmer oceans cause corals to expel zooxanthellae ✔
g. bleaching due to death/expulsion of mutualistic organisms/algae ✔
Allow zooxanthellae instead of algae in mpf.
Reject reacts and diffuses instead of dissolves in mpa.