Water:
• Rising temp
Positive feedback – More evaporation, atmosphere holds more water in clouds, increased
absorption of long wave-radiation.
• Decreasing temp
Negative feedback – More atmospheric vapour in clouds cover, reflected solar radiation,
less radiation absorbed.
• Increased precipitation and a drainage basin water cycle
Negative feedback – Increased run-off, increased river flow, recharges aquifers and water
storage in permeable rocks.
• Decreased precipitation and a tree (small scale)
Negative feedback – Drought, shallow roots insufficient for water demand, reduces
transpiration loss through leaf fall.
Carbon:
• Fertilisation in the biosphere
Negative feedback – Rising atmospheric CO2 levels increase photosynthesis and stimulate
plant growth. Carbon eventually transferred into long term soil and ocean sediment stores.
Increased PP dependent on light, soil nutrients, nitrogen and water. In the Amazon
increased PP could be due to lower rainfall and increased sunlight, not CO2 levels.
NASA – now land is absorbing 1.1 billion tonnes more carbon than its releasing. However we
cannot depend on natural mechanisms to mitigate increasing anthropogenic emissions.
• Global Warming
Positive feedback – Intensifies carbon cycle, speeding decomposition and CO2 emissions.
• The Tundra
Positive feedback – Global warming occurring at fastest rate (2 degrees in 30yrs). Sea ice and
snow reduction has exposed sea and land, so more sunlight is absorbed, melting
permafrost.
