BRAINCAKEHuman Influence
Before the Industrial Revolution (around 1750), the concentration of CO2 in the atmosphere was about 280 ppm (parts per million). It has now risen above 420 ppm, higher than at any time in at least 800,000 years. Two human activities are mainly responsible.
Burning fossil fuels (coal, oil and gas) for electricity, transport and industry releases carbon that was locked away for millions of years. This is by far the largest human source of CO2.
Deforestation adds CO2 in two ways: burning or decay of the cleared trees releases their stored carbon, and fewer trees remain to remove CO2 by photosynthesis.
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All 20 lessons in The Efficiency of Ecosystems · All Edexcel A-level Biology topics