Lesson 2 of 9 / Climate change, food and disease vectors
Trace ice, water and warming feedbacks
Which effects add sea water, and which amplify warming?
In this lesson: Explain sea-level rise, changing extremes, fresh-water stress and greenhouse-gas release from thawed organic matter.
About 6 min
The key ideaWarming can melt land ice, expand sea water, intensify several weather extremes and disrupt fresh-water supplies. Thawing frozen organic matter can release gases that add further warming.
Explore the idea
Separate sea level and warming feedbacks
Melting ice stored on land adds water to the ocean. Warming sea water also expands; these are two contributors to sea-level rise.
The diagrams isolate mechanisms. They are not a sea-level prediction or a scale drawing.
Explanation
Warming melts polar land ice and glaciers, adding water to the ocean. Sea water also expands as it warms. Both contribute to sea-level rise. Floating sea ice already displaces water, so its melting does not directly raise sea level in the same way; loss of bright ice can nevertheless increase absorption of sunlight and amplify warming.
A warmer climate increases the likelihood or intensity of many heat extremes and can alter heavy rainfall and drought. The pattern differs among regions and types of event: it is inaccurate to say every kind of extreme becomes more frequent everywhere. A single storm also cannot by itself establish a long-term climate trend.
Fresh-water supplies can be stressed by greater evaporation, prolonged dry periods, disrupted snow or glacier melt, and increased demand during heat. Floods can contaminate supplies, while sea-level rise can increase saltwater intrusion into coastal groundwater. More water somewhere is not the same as more safe fresh water where people and ecosystems need it.
Thawing permafrost exposes previously frozen organic matter to microbial decomposition. Carbon dioxide can be released, and waterlogged low-oxygen conditions can favour methane production. These greenhouse gases can strengthen warming and cause further thaw: a positive feedback amplifies the initial change rather than counteracting it.
Step by step
- 1
Identify the physical change
Specify land-ice melt, thermal expansion, a weather change or thaw.
- 2
Follow its consequence
Connect to sea level, water availability or decomposition.
- 3
Close a feedback only when justified
Released greenhouse gases can add warming and further thaw.
Worked example
Separate direct sea-level effects
Why should an explanation of rising sea level distinguish melting land ice from melting floating sea ice?
One way to explain it
Land-ice melt adds water that was previously stored on land, while floating ice already displaces water. Warming sea water also expands. Sea-ice loss can amplify warming through lower reflectivity, but is not the same direct addition of water as land-ice melt.
Why this answer works
- Identify whether the water was already floating in the ocean.
- Separate a direct volume effect from an indirect warming feedback.
Is this true? "Positive feedback means an environmentally beneficial change."
Positive describes amplification. Thaw, gas release and further warming reinforce one another; the term does not judge the effect as good.