Increasing concentrations of carbon dioxide (CO2) in the atmosphere are making the oceans more acidic—in other words, lowering the pH of ocean water. Worldwide, the average pH of the upper ocean—the top 1,000 m—has declined 0.12, to 8.1, between 1750 and 2010. If humans continue to emit greenhouse gases at current rates, atmospheric CO2 concentrations will reach 500 parts per million (ppm) by 2050 and 800 ppm by 2100, by which time the pH of the upper ocean could drop to 7.8 or 7.7. The deep ocean—below 4,000 m—had a pH of 8.2 in 2010. At that depth, acidity is relatively stable and not expected to increase as quickly, as is shown in the graph labeled Long-Term Graph. The base of the ocean food web is phytoplankton, which, like plants, use sunlight for photosynthesis and thus can live only in the upper ocean. For many types of phytoplankton, acidification makes it harder to absorb iron, a vital nutrient. Research suggests that a 0.3 decline in pH reduces phytoplankton iron consumption by about 15 percent, slowing photosynthesis and impacting growth and reproduction. Comparable changes in the past correlated with massive extinctions of sea life.This scatter plot shows oceanic CO2 concentrations reported in partial pressure (pCO2) and water acidity reported in pH, from 1985 to 2005. Each dot represents a specific measurement in the upper ocean. The curves are statistical-based models representing statistical trends derived from the measurements. https://gmatclub.com/forum/download/file.php?mode=view&id=75402 Refer (attachment 1- scatter plot) belowIn the graph, ΔpH refers to change or predicted change in pH of ocean water since the pre-1750 period, expressed in relation to water depth and year. Refer (attachment 2 - long term graph) below: https://gmatclub.com/forum/download/file.php?mode=view&id=75401 1 - Scatter plot.png 2 - Long term graph.png

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Increasing concentrations of carbon dioxide (CO2) in the atmosphere

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14 May 2026, 22:12

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Projection doesn't mean 100 percent truth

Projection just means what can be possibly said or predicted about certain events.

Past co-related events can be used as premise to conclude that event can be repeated in future.

Hope this helps.

user84525084572

I also struggled quite a bit with Question 1.

It is very important to look carefully at the exact wording in both the question and the text.

In my opinion, the most important part is in the question stem: “Assuming that current trends will continue.”
This means a projection must be based on ongoing trends, not just historical events.

The text says:
“Comparable changes [decreased iron absorption by phytoplankton] in the past correlated with massive extinctions of sea life.”

The problem is that this refers to past correlation, not a current trend. Just because two things were correlated in the past does not mean the same pattern is happening now or will continue in the future.

Therefore, we cannot logically project that:
“Decreased iron absorption by phytoplankton will contribute to increased extinctions of sea life.”

So the correct answer should be “Not projected.”

GMATNinja Am I missing something, or is the official solution incorrect?