---
title: "Henry's Law | Intro to Climate Science"
description: "Henry's Law says gas dissolved in water rises with that gas's partial pressure above it, explaining CO2 uptake and ocean acidification in climate science."
canonical: "https://fiveable.me/introduction-climate-science/key-terms/henrys-law"
type: "key-term"
subject: "Intro to Climate Science"
unit: "Unit 11"
---

# Henry's Law | Intro to Climate Science

## Definition

Henry's Law says the amount of a gas dissolved in a liquid is proportional to that gas's partial pressure above the liquid at constant temperature. In climate science, it explains how oceans absorb CO2.

## What It Is

Henry's Law is the rule that tells you how much gas a liquid can hold at a given temperature. In Intro to Climate Science, you use it to explain why ocean water absorbs more carbon dioxide when the air above it has more CO2.

The core idea is simple: if the partial pressure of a gas goes up, more of that gas dissolves into the liquid. For carbon dioxide, that means a higher atmospheric CO2 level pushes more CO2 into the ocean surface. The standard shorthand is C = kH × P, where C is dissolved gas concentration, kH is Henry's Law constant, and P is the gas's partial pressure.

This is not just a math relationship, it is a mechanism. The ocean surface and the air above it are constantly exchanging gas molecules. When CO2 molecules hit the water, some dissolve. If the air has a lot of CO2, the balance shifts so that more molecules enter the water than leave it.

Temperature changes the picture too. Cooler water generally holds more dissolved gas, while warmer water holds less. That is why cold surface waters can take up more CO2 than warm waters, and why warming oceans can become weaker carbon sinks over time.

Once CO2 dissolves, it does not just sit there harmlessly. It can react with water to form carbonic acid, which can lower pH and reduce carbonate ion availability. That chain reaction is why Henry's Law shows up again and again in lessons on ocean chemistry, sea level rise, and ocean acidification.

A useful way to think about it is this: Henry's Law is the first step in the story of how atmospheric CO2 enters the ocean. After that step comes chemistry inside the water, and those later reactions are what affect marine organisms, seawater pH, and carbonate minerals.

## Why It Matters

Henry's Law is one of the simplest ways to connect the atmosphere and the ocean in climate science. It explains why a rise in atmospheric CO2 does not just stay in the air, but also changes seawater chemistry by increasing the amount of dissolved CO2 at the surface.

That matters because the ocean does not absorb carbon dioxide evenly or indefinitely. Surface waters take up CO2 based on temperature and partial pressure, so the law helps you predict where uptake is faster and where it is weaker. Cold, high-latitude waters often absorb more CO2 than warm tropical waters, which is one reason ocean carbon uptake varies by region.

The law also sets up the chemistry behind ocean acidification. More dissolved CO2 can lead to more carbonic acid, which can lower pH and reduce carbonate ions. That chain is central to understanding why calcifying organisms like corals and shellfish have a harder time building shells and skeletons in acidifying waters.

In climate topics, Henry's Law is also a bridge concept. It links greenhouse gas concentration, ocean absorption, carbon cycle behavior, and marine ecosystem impacts in one mechanism. If you can explain this law clearly, you can usually explain a large part of the ocean acidification story without getting lost in extra chemistry.

It also helps with interpretation. When you see a graph of rising atmospheric CO2, warming sea surface temperatures, or changing ocean pH, Henry's Law gives you the cause-and-effect logic for why those trends are connected.

## Connections

### Carbon Dioxide

Carbon dioxide is the gas most often discussed with Henry's Law in climate science because its rising atmospheric concentration drives more ocean uptake. The law explains the physical transfer from air to water, while CO2 chemistry explains what happens after it dissolves. Together, they connect emissions to ocean acidification.

### Ocean Acidification

Henry's Law is one of the first steps in ocean acidification. It increases dissolved CO2 in seawater, and that dissolved CO2 can form carbonic acid and lower pH. If you are tracing the full process, Henry's Law comes before the pH change, not after it.

### Partial Pressure

Partial pressure is the variable Henry's Law uses to measure how much of a gas is pushing on the liquid. When the partial pressure of CO2 rises in the atmosphere, the ocean absorbs more of it. This is the pressure difference that drives gas exchange at the surface.

### [Carbonic Acid](/introduction-climate-science/key-terms/carbonic-acid)

Carbonic acid forms after CO2 dissolves in water. Henry's Law does not create the acid directly, but it increases the amount of dissolved CO2 available for the reaction. That makes carbonic acid the next chemical step in the ocean acidification chain.

## On the AP Exam

A quiz question might give you an atmospheric CO2 increase and ask what happens to dissolved CO2 in seawater. Henry's Law tells you to predict more gas dissolving into the ocean, especially if temperature stays constant. On a problem set, you may use C = kH × P to compare two situations with different partial pressures.

In a data analysis question, you might look at a graph of ocean pH, surface temperature, or CO2 concentration and explain the pattern using gas solubility. If the water warms, you should connect that to lower gas solubility and reduced CO2 uptake. If the question mentions corals or shellfish, you should extend the answer to acidification and carbonate ion loss.

## Key Takeaways

- Henry's Law says dissolved gas concentration increases when the gas's partial pressure above the liquid increases, as long as temperature stays the same.
- In climate science, the law explains why rising atmospheric CO2 leads to more CO2 dissolving into the ocean surface.
- Warmer water holds less dissolved gas, so warming oceans generally absorb less CO2 than colder waters.
- Henry's Law is the starting point for ocean acidification, because dissolved CO2 can form carbonic acid and lower seawater pH.
- If you can track the path from atmospheric CO2 to dissolved CO2 to lower pH, you are using Henry's Law correctly.

## FAQs

### What is Henry's Law in Intro to Climate Science?

Henry's Law says that the amount of a gas that dissolves in a liquid is proportional to that gas's partial pressure above the liquid at constant temperature. In climate science, it explains why higher atmospheric CO2 leads to more CO2 entering the ocean surface.

### How does Henry's Law relate to ocean acidification?

Henry's Law explains the first step in the process. More CO2 dissolves into seawater when atmospheric CO2 rises, and that dissolved CO2 can form carbonic acid, which lowers pH and changes ocean chemistry.

### Why does warmer water absorb less CO2?

Gas solubility usually drops as temperature rises, so warm water holds less dissolved gas. In climate science, that means warmer oceans are less effective at absorbing atmospheric CO2 than colder oceans.

### What is the formula for Henry's Law?

A common form is C = kH × P, where C is the concentration of dissolved gas, kH is Henry's Law constant, and P is the gas's partial pressure above the liquid. The exact constant can depend on the gas and temperature.

## Related Study Guides

- [11.2 Sea level rise and ocean acidification](/introduction-climate-science/unit-11/sea-level-rise-ocean-acidification/study-guide/Cs2adHIJZEu7GQV8)

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