2.2 Consequences of global climate change

The question asks why floating sea ice melt does not raise sea level. The relevant principle is Archimedes' law: a floating object displaces its own weight (mass) in water.

When Arctic sea ice floats, it already pushes down a volume of water equivalent to its own mass. When it melts, the liquid water produced occupies exactly that displaced volume — so net sea level change is essentially zero.

Only land-based ice (glaciers, ice sheets) adds genuinely new water to the ocean when it melts, because it was stored outside the ocean system entirely. This is why Greenland and Antarctic ice sheets pose a far greater sea-level threat than Arctic sea ice.

The first option correctly identifies the displacement principle as the reason melting floating sea ice does not raise sea level. The other options introduce incorrect claims about salinity, ocean size, or melt rate that are not the actual physical explanation.

The question asks for the accurate physical explanation for why Arctic sea ice loss has minimal impact on sea level — so we need the option that correctly applies the physics of floating objects.

The option about saltwater density and volume cancellation is scientifically inaccurate; the displacement principle, not salt density differences, is the correct explanation.

The claim that 'the Arctic Ocean is too small' is irrelevant and incorrect — the mechanism is not about ocean size but about whether the ice was already displacing water before it melted.

The argument that Arctic sea ice melts 'too slowly' confuses the rate of melt with the principle that explains why even complete melting would not raise sea level — rate is irrelevant here.

The first option accurately applies Archimedes' principle: floating ice already displaces its own mass of water, so its melting adds no net volume to the ocean.

The question is about interpreting pH changes correctly. pH is defined as the negative logarithm (base 10) of hydrogen ion concentration: $pH=-{\log }_{10}[H^{+}]$.

A change of 0.1 pH units means $[H^{+}]$ changes by a factor of $10^{0.1}\approx 1.26$, i.e. a ~26% increase in hydrogen ion concentration. Treating the pH scale as linear and calculating 0.1/8.2 ≈ 1.2% is a fundamental misuse of the scale.

The student divided 0.1 by 8.2 as if pH were a linear quantity — for example, like temperature in Celsius. Because pH is logarithmic, each unit change represents a tenfold difference in acidity, so partial-unit changes still represent substantial percentage shifts in actual ion concentration.

The correct answer is the first option, which accurately explains the logarithmic nature of the pH scale and gives the correct approximate magnitude of the acidity increase (~26–30%).

The question tests understanding of the logarithmic pH scale and why small numerical pH changes represent large real changes in hydrogen ion concentration.

The claim that deeper ocean layers have acidified more on a linear scale is irrelevant to why the surface pH drop of 0.1 is significant — it also misrepresents the scale issue entirely.

pH measures hydrogen ion $[H^{+}]$ concentration, not hydroxide ions $[O{H}^{-}]$. This option contains a factual error and does not address the logarithmic scale question.

Acidity can perfectly well be expressed as a percentage change in ion concentration; the problem is not units but the student's incorrect linear interpretation of a logarithmic scale.

Only the first option correctly identifies the logarithmic nature of pH and explains that a 0.1-unit drop corresponds to roughly a 26–30% increase in hydrogen ion concentration.