2.1 Causes of global climate change

The bar chart plots total annual CO₂ emissions in megatonnes (Mt) — a single quantitative variable on the y-axis against country on the x-axis. This means it can only support conclusions about total national output, nothing else.

Country X has the tallest bar at 1,200 Mt, followed by W (400 Mt), Y (280 Mt), and Z (55 Mt). On a total-emissions basis, X ranks highest, which directly supports the first option.

Per capita figures require population data not shown on the chart, so conclusions about per capita rank (options 3 and 4) cannot be drawn. Option 2 makes a normative claim about responsibility that goes beyond the chart's measurement of totals.

Only the statement that Country X has the highest total annual emissions among the four is directly readable from the bar chart. All other options require data — per capita figures, HIC status, lifestyle data — that the chart alone does not provide.

The question asks which conclusion is best supported by the bar chart alone — this signals we must not import external information such as population or development status beyond what the chart provides.

'Country W is most responsible because it is a HIC' introduces a normative judgement about responsibility and references HIC status — neither of which the chart itself measures or displays.

'Country Z has the lowest per capita emissions' and 'Country Y's lower total confirms a less energy-intensive lifestyle' both require per capita calculations using population data absent from the chart. A total-emissions bar chart cannot confirm per capita rank.

'Country X contributes the most in total annual terms' is directly readable from the bar heights — X's bar is tallest at 1,200 Mt. This is the only claim that requires only the bar chart data, making it the correct answer.

Wien's displacement law states that the wavelength of peak radiation emission is inversely proportional to the temperature of the emitting body. A hotter object emits more intensely and at shorter wavelengths than a cooler one.

The Sun's surface is approximately 5,800 K, so it emits predominantly shortwave radiation (visible light, ultraviolet). Earth's surface is roughly 288 K (15°C), so it re-emits energy as longwave (infrared) radiation. The relationship is temperature → wavelength, not distance or reflection.

Distance from Earth has no bearing on the wavelength at which the Sun emits. Reflection by clouds redirects existing radiation — it does not create new shortwave radiation. Earth's absorption of longwave radiation does not control what wavelengths the Sun emits.

The correct answer links the Sun's high surface temperature (~5,800 K) directly to the physical principle that hotter bodies emit at shorter wavelengths, producing solar radiation predominantly in the visible and UV spectrum.

The question asks for the physical explanation of why solar radiation is 'shortwave' — this requires applying the temperature–wavelength relationship, not geography of the solar system.

'Hotter bodies emit at longer wavelengths' inverts the actual relationship — it is the opposite of what Wien's law states. Distance from Earth is irrelevant to emission wavelength.

Cloud reflection redirects already-emitted radiation — it does not generate shortwave radiation. The Sun emits shortwave radiation directly from its surface, independent of cloud interaction.

What the Earth absorbs or does not absorb has no causal effect on the wavelengths at which the Sun emits radiation — these are governed entirely by the Sun's own surface temperature.

Only option 1 correctly applies the inverse temperature–wavelength relationship: the Sun is very hot (~5,800 K), so it emits predominantly at short wavelengths in the visible and UV spectrum.