pH and climate change

Definition

pH is a quantitative measure of the acidity or basicity of a solution. The pH scale assigns a value between 0 and 14 based on the concentration of the hydrogen ions in the solution. The more hydrogen present, the more acidic the solution and the lower the pH value. The fewer hydrogen ions present, the less acidic the solution and the higher the pH value. Pure water, which is neutral (neither acidic nor alkaline) has a pH of 7, which means that the concentration of the hydrogen ions is 10^-7 gram-equivalent per liter. This mathematical system of stating pH was developed by a Danish chemist, Søren Peter Lauritz Sørensen, around 1909. “pH” is thought to be an abbreviation for the “potential of hydrogen” in English. The same abbreviation makes sense in several other languages, as it could stand for pondus hydrogenii or potentia hydrogenii in Latin or potentiel hydrogene in French.

Significance for Climate Change

Arguably, the single most important property of the moisture that is provided to soil is its pH. Soil’s acidity determines which kinds of plants are able to grow in that soil. It is possible to adjust the pH of soil or of the water provided to it; acidic soil can be treated with lime to “sweeten” or neutralize it.

Acidic soil is usually considered to be infertile, as most conventional crops will not grow in it. Soil acidity also causes certain metals, such as aluminum and manganese, to become more soluble in the soil; many plants will not tolerate more than tiny quantities of these metals. Of the seventeen essential nutrients a plant needs to grow, it gets fourteen of them from the surrounding soil. The soil’s pH is an important factor in the solubility and availability of these nutrients.

Soil acidity can be increased by aspects of the global climate. For example, acid rain (rain with a pH of 5.6 or lower) acidifies the soil upon which it falls. Other contributors to soil acidity include the oxidation of sulfur compounds that occurs when salt marshes are drained to be used as farmland, as well as the addition of fertilizer salts that hydrolyze, or the addition of microbes that decompose organic materials. The pH of soil can be determined using a pH meter, a device that uses electrodes in the soil to generate a weak charge that can measure the concentration of hydrogen ions. Indicator dyes are also used in determining soil pH; these dyes are mixed into soil suspensions and matched against a color chart.

Acidity is also important in bodies of water. When water becomes polluted, the temperature of the water increases, and excess nutrients are formed. This causes greater algal and plant growth in the water, which may increase acid levels. These increased levels can greatly change the solubility of all the chemicals in the water, affecting the entire ecosystem. For example, if changes in pH increase the solubility of phosphorus, that increase may in turn increase plant growth, eventually generating a greater demand for dissolved oxygen in the water and decreasing the availability of oxygen to fish. pH is also important in seawater simply because different types of marine plants and animals are able to survive in acidic or alkaline environments, so the pH of an ocean region helps determine the inhabitants of that region.

Bodies of water have a natural ability to buffer changes in the pH, so adding acids or bases to the water does not generally change the pH value as much as one might expect. (The pH values throughout a body of water may vary naturally. At the bottom of a lake, for example, the pH may be lower than at the top, perhaps between 6.5 and 7.5. At the top of a lake during the summer, pH may range from 7.5 to 8.5.) However, the ability of a body of water to buffer changes in pH is greatly affected by acid rain. When the water absorbs great quantities of acid from rain, it loses its buffering ability, and even a slight addition to the water, such as from more rain or from snowmelt, will then alter its pH.

Some microorganisms are able to affect the pH of their environment. For example, when food is pickled, microbes are used to acidify and preserve it. However, microbes used in farming and agriculture can also affect soil and water quality when they acidify the soil or, through runoff, the water.

Research by scientists in the 2020s showed that global climate change could have devastating effects on the pH of the world's oceans. Mean surface ocean pH is projected to decline further, between about 0.15 and 0.5pH units by 2100, depending on the emission scenario. This would affect many marine organisms and could alter marine ecosystems.

Bibliography

Date, R. A., et al., eds. Plant-Soil Interactions at Low pH: Principles and Management. Kluwer Academic, 1995.

Liou, Joanne. "What Is Ocean Acidification?" International Atomic Energy Agency, 8 June 2022, www.iaea.org/newscenter/news/what-is-ocean-acidification. Accessed 27 Sept. 2025.

“Ocean Acidification.” European Environment Agency, 29 May 2024, www.eea.europa.eu/en/analysis/indicators/ocean-acidification. Accessed 27 Sept. 2025.

Rengel, Zdenko., ed. Handbook of Plant Growth: pH as the Master Variable. CRC Press, 2002.

Rengel, Zdenko, ed. Handbook of Soil Acidity. Taylor & Francis Group, 2003.