science

Revelle factor

Revelle factor is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Revelle factor rather than just read about it. In short: The Revelle factor (buffer factor) is the ratio of instantaneous change in carbon dioxide (CO2) to the change in total dissolved inorganic carbon (DIC), and is a measure of the resistance to atmospheric CO2 being absorbed by the ocean surface layer. The buffer factor is used to examine the distribution of CO2 between the atmosphere and the ocean, and measures the amount of CO2 that can be dissolved in the mixed surf…

Key takeaways

Revelle factor belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Revelle factor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Revelle factor from memory before moving on to harder problems.

Reference excerpt

The Revelle factor (buffer factor) is the ratio of instantaneous change in carbon dioxide (CO2) to the change in total dissolved inorganic carbon (DIC), and is a measure of the resistance to atmospheric CO2 being absorbed by the ocean surface layer. The buffer factor is used to examine the distribution of CO2 between the atmosphere and the ocean, and measures the amount of CO2 that can be dissolved in the mixed surface layer. It is named after the oceanographer Roger Revelle. The Revelle factor describes the ocean's ability to uptake atmospheric CO2, and is typically referenced in global carbon budget analysis and anthropogenic climate change studies.

Revelle factor = ⁠Δ[CO2]/ [CO2]⁠ / ⁠Δ[DIC]/[DIC]⁠ where Δ[CO2] / [CO2] is the instantaneous change in pCO2 and Δ[DIC] / [DIC] is the instantaneous change in dissolved inorganic carbon at the oceans surface.

Thermodynamics In order to enter the ocean, carbon dioxide gas has to partition into one of the components of carbonic acid: carbonate ion, bicarbonate ion, or protonated carbonic acid, and the product of these many chemical dissociation constants factors into a "back-pressure" that limits how fast the carbon dioxide can enter the surface ocean.

DIC The species of DIC present in ocean waters are dependent on the pH of the system, and are illustrated by the Bjerrum plot below (Figure 1). Carbonate is dominant in higher pH (basic) environments, whereas carbon dioxide is dominant in lower pH (acidic) environments. Bicarbonate ions are abundant in relatively mid-pH waters. As the pH decreases, most of the DIC will be present as CO2 and hence increases its partial pressure (pCO2), and the buffer factor will increase. An increased buffer factor results in a decreased buffering effect, which could lead to the uptake of more CO2 from the atmosphere, and decreasing the pH even more. Figure 1: Curves illustrating the molar fraction of carbonate species present in seawater across pH, with salinity set at 5,000ppm, and temperature set to 25 degrees Celsius. Note temperature and salinity affect carbonate species present, and vary with location and season.

DIC and alkalinity govern carbonate and acid-base chemistry in the world's oceans, and their effects on the Revelle factor is no exception. The ratio of DIC to total alkalinity, and the changes in pCO2 are the main cause of Revelle Factor variability. Higher levels of DIC result in a lower Revelle factor, and consequently a larger buffering effect. Higher levels of pCO2 results in a higher Revelle factor, a positive feedback loop, and consequently a smaller buffering effect. Typically, the buffer factor ranges between 8 and 13.

Anthropogenic CO2 The capacity of the ocean waters to take up surplus (anthropogenic) CO2 is inversely proportional to the value of the Revelle factor. Hence, in modern-day oceans, it is possible to see the concentrations of anthropogenic CO2 by measuring the Revelle factor; the lower the Revelle factor, the greater the amount of anthropogenic CO2. Low Revelle factors are typically found in the warmer tropical to subtropical waters, whereas higher Revelle factors are found in the colder high latitude waters of the North Atlantic. The North Pacific has higher Revelle factors, and has lower anthropogenic CO2. This is due to the fact that the alkalinity values in the North Pacific are as much as 100μmol/kg lower than those in the North Atlantic.

The Revelle effect The Revelle effect describes how only a small fraction of pCO2 is present in ocean water when much larger amounts are added to the atmosphere. Depending on the alkalinity of the water, DIC is either present as CO3, HCO3, or CO2. When the pH is high (basic) the buffering effect is greatest, causing much of the DIC to exist as HCO3 or CO3, and not CO2. So, the greater the buffering effect (low Revelle Factor) the more DIC occurs as CO3 or HCO3, effectively lowering the pCO2 levels in both the atmosphere and ocean.

Worked examples

Example 1 — a first encounter with Revelle factor

Start with the simplest possible case. Write down what Revelle factor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Revelle factor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Revelle factor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Revelle factor

In research: Revelle factor appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Revelle factor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Revelle factor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbon dioxide, so understanding it makes those chapters shorter.
In everyday life: Look for Revelle factor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Revelle factor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Revelle factor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Revelle factor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Revelle factor in simple terms?

Why does Revelle factor matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Revelle factor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Revelle factor.