Climate Change is altering rainfall’s chemistry

by Robert Marcos, photojournalist

Climate change is altering the chemical makeup of rainfall. It’s increased the concentration of dissolved carbon dioxide which makes rainfall more acidic¹. At the same time it has shifted the levels of atmospheric pollutants that wash out when it rains. This changing chemistry is a problem because it alters how water interacts with soils, plants, aquatic systems, infrastructure, and even the atmosphere itself. Increased acidity in rainfall acts as a chemical catalyst that destabilizes both terrestrial and aquatic environments through the following mechanisms²

• Nutrient Leaching: Acidic rain strips the soil of essential buffering minerals and nutrients—such as calcium, magnesium, and potassium—which are vital for plant cell structure and growth.
• Heavy Metal Mobilization: As soil pH drops, naturally occurring but normally stable metals like aluminum become soluble. This “mobile” aluminum is toxic to plants, damaging root systems and preventing them from absorbing water.
• Microbial Disruption: Many beneficial soil bacteria and fungi are sensitive to pH changes. Increased acidity can suppress the microbial activity responsible for decomposition and nitrogen fixation, ultimately reducing soil fertility.
• Biological Stress and Mortality: Many aquatic species have narrow tolerance ranges. At a pH of 5.0, most fish eggs cannot hatch, and lower levels can lead to the death of adult fish, amphibians, and insects like mayflies.
• Gill Damage: Soluble aluminum leached from nearby soil enters waterways and clogs the gills of fish. This impairs their osmoregulation and ability to breathe, often serving as the primary cause of fish kills in acidified lakes.
• Food Web Collapse: The loss of acid-sensitive “base” species, such as certain plankton and invertebrates, triggers a cascade effect that starves larger predators and simplifies the entire ecosystem.

Effects on Agricultural Production

The chemical and physical shifts in rainfall are fundamentally destabilizing the economic foundations of global food systems³.

• Declining Crop Productivity: For every 1°C of warming, global yields of major staples are projected to decline significantly: maize by 7.4%, wheat by 6.0%, and rice by 3.2%.
• Nutritional Degradation: Increased atmospheric and altered soil chemistry reduce the concentrations of protein and essential minerals like zinc and iron in crops like wheat and soybeans.
• Increased Costs: Farmers must spend more on lime to neutralize soil acidity and additional fertilizers to replace leached nutrients like calcium and magnesium.
• Direct Foliar Damage: Acidic rain erodes the waxy cuticle of leaves, making plants more vulnerable to dehydration, pests, and diseases.

Impacts on Commercial Fishing

Marine fisheries and seafood industries, which supported $319 billion in sales in 2023, face major disruptions as fish stocks move toward cooler poles or become less productive⁴.

• Catch Potential Losses: Tropical regions are predicted to see declines of up to 40% in potential seafood catch by 2050 due to warming and acidification.
• Shellfish Vulnerability: Ocean and coastal acidification (exacerbated by acidic runoff) hinder calcification, weakening the shells of oysters, clams, and scallops. This is estimated to cause consumer losses of $480 million per year by the end of the century.
• Ecosystem Collapse: Acidified freshwater and marine environments disrupt reproductive cycles; for instance, at a pH of 5, most fish eggs cannot hatch, leading to the collapse of local populations and the industries that rely on them.

Impacts on Water Infrastructure

More acidic rainfall significantly deteriorates water infrastructure by accelerating the chemical breakdown of both metallic and cement-based materials. When rainwater’s pH drops—oftenhttps://www.gov.nl.ca/eccc/files/waterres-reports-drinking-water-study-on-ph-adjustment-systems-task-7-study-report.pdf due to sulfuric and nitric acids—it becomes highly corrosive, leading to structural damage and water quality issues. Acidic water targets the internal and external surfaces of the pipes that transport water.⁵

• Chemical Dissolution: Acidic rain reacts with the calcium carbonate and calcium hydroxide in concrete, dissolving these components and leaving the structure porous and weak.
• Structural Failure: As the concrete matrix dissolves, the protective layer around steel reinforcements (rebar) can fail. Corroding steel expands up to six times its size, creating internal pressure that cracks the surrounding concrete.
• Surface Erosion: Prolonged exposure causes surface “spalling” or peeling, exposing coarse aggregates and increasing maintenance costs for bridges, dams, and treatment basins.

Challenges for Water Treatment

• Water treatment facilities must expend more resources to manage increasingly acidic sources of water.
• Increased Neutralization Costs: Facilities must add more alkaline substances, such as caustic soda or soda ash, to raise the pH to a non-corrosive range (typically 6.5 to 8.5).
• Disinfection Interference: Efficient chlorination is more difficult in water that is too acidic or too basic, potentially requiring higher chemical doses to ensure safety.
• Contaminant Mobilization: Acid rain leaches aluminum and other minerals from the surrounding soil into reservoirs, requiring more complex filtration to remove these additional contaminants.⁶