By the end of this lesson
- Explain how increased greenhouse gases cause an enhanced greenhouse effect.
- Describe possible consequences of global warming.
- Use conditional language when evaluating predictions.
BIG QUESTION
How confident can we be about the consequences of global warming?
The link between more greenhouse gas and warming is well supported; the size and local pattern of consequences vary.
The enhanced greenhouse effect
Higher concentrations of greenhouse gases absorb and re-emit more infrared radiation back towards the surface. This is the enhanced greenhouse effectExtra warming of the Earth caused by human activities increasing the concentration of greenhouse gases, so more infrared radiation is trapped..
The result is an increase in the mean temperature of the Earth’s surface and lower atmosphere, called global warmingAn increase in the average temperature of the Earth's surface, linked to the enhanced greenhouse effect.. Measurements show a rise in global mean temperature over the past century alongside rising carbon dioxide.
Physical consequences
Melting glaciers and ice sheets, and the expansion of warmer seawater, cause sea levels to rise, which may flood low-lying land.
climate changeA long-term change in global weather patterns and average temperatures, linked to the enhanced greenhouse effect. may also alter rainfall patterns and increase the frequency of some extreme events such as heatwaves, droughts and heavy rainfall, although effects differ between regions.
Biological consequences
Species may shift their distribution towards the poles or to higher altitudes. Species that cannot move or adapt quickly enough may decline, reducing biodiversityThe variety of living organisms in an area, which can be described by species richness and evenness, and also includes genetic diversity..
Warmer oceans can cause coral bleaching; changing seasons can mismatch the timing of flowering and pollinators; crop yields may rise in some regions and fall in others; and the range of some disease vectors, such as mosquitoes, may expand.
Evaluating evidence
Data such as ice cores and temperature records show correlation between greenhouse gas concentration and temperature, and the physical mechanism explains the link.
Predictions of future change depend on future emissions and on feedbacks, so they are given as ranges. Use words such as “may” and “is likely to” when describing consequences.
Consequences of global warming
Link the cause to a consequence and a biological effect.
| Change | Possible consequence | Biological effect |
|---|---|---|
| Ice melting and sea expansion | Sea-level rise. | Loss of coastal habitats and farmland. |
| Altered rainfall | More drought or flooding in some regions. | Changes in crop yields and plant distribution. |
| Warmer oceans | Coral bleaching. | Loss of reef biodiversity. |
| Shifting climate zones | Species migrate towards poles or uphill. | Some species decline or become extinct. |
| Warmer winters | Longer insect breeding seasons. | Pests and disease vectors may spread. |
Language that earns precision
- enhanced greenhouse effect
- Extra warming caused by increased concentrations of greenhouse gases from human activity.
- global warming
- An increase in the Earth’s mean surface temperature.
- climate change
- Long-term change in patterns of temperature, rainfall and weather.
Common misconceptions
Claim: Global warming means every place gets warmer every year.
Correction: It refers to a long-term rise in mean global temperature; local weather varies.
Claim: Melting sea ice is the main cause of sea-level rise.
Correction: Floating sea ice has little effect; melting land ice and thermal expansion are the main causes.
Claim: All species will be harmed.
Correction: Some species may benefit or expand their range, while others decline.
Match the answer to the command word
Link: more greenhouse gases → more infrared absorbed and re-emitted → enhanced greenhouse effect → global warming.
Consequences “may” or “are likely to” occur; avoid stating predictions as certainties.
Recall, apply, then justify
Explain how an increase in carbon dioxide may lead to global warming.
Hint
Infrared, re-emission, temperature.
Suggested marking points
- More carbon dioxide absorbs more infrared radiation emitted by the Earth.
- More is re-emitted back towards the surface (enhanced greenhouse effect).
- So the mean temperature of the Earth increases.
Describe two possible biological consequences of global warming.
Hint
Think about distribution, coral, crops or disease.
Suggested marking points
- One consequence, for example species migrating to cooler areas or extinction.
- A second consequence, for example coral bleaching, changes to crop yields or spread of disease vectors.
Butterfly species in the UK have been recorded further north over 40 years (illustrative scenario). Evaluate whether this is evidence for global warming.
Planning hint
Consistent with prediction; consider other causes and data quality.
What a strong design includes
- The shift is consistent with species moving to stay within suitable temperatures.
- It matches predictions from global warming.
- Changes in habitat or land use could also explain the shift.
- Recording effort may have increased in the north.
- Temperature records for the same areas would strengthen the link.
- Similar shifts in many unrelated species would be stronger evidence.