Short/Long term changes

• Diurnal changes in carbon

  1. Significant changes occur within 24 hour period

  2. During day CO₂ flows from atmosphere to vegetation through photosynthesis and respiration

  3. Photosynthesis controlled by light, none at night

  4. At night CO₂ from vegetation to atmosphere through respiration and decay
• The diurnal range in CO₂ can be as great as 100ppm
• Diurnal water cycles


  1. Lower temperatures at night reduce evaporation and transpiration

  2. Convectional precipitation, dependent on direct heating of the ground by the sun, is a daytime phenomenon often peaking in the afternoon

  3. At night temperature cools and reaches the dew point
• Seasonal changes in carbon

  1. Seasons controlled by variations in the sun's intensity

  2. Seasonal variations in the carbon cycle shown by month to month changes in the net primary productivity of vegetation (photosynthesis)

  3. In mid/high latitudes, day length and temperature drive seasonal changes

  4. In the tropics, seasonal changes are driven by water availability

  5. Northern hemisphere summer - trees have full foliage, net global flow of CO₂ from atmosphere to biosphere, CO₂ levels fall

  6. End of summer as photosynthesis ends, flow reversed with natural decomposition releasing CO₂ back to atmosphere
• During the growing season, continental land masses in the northern hemisphere ecosystems extract huge amounts of CO₂ from the atmosphere
• In the Amazon dry season, there are less clouds which leads to more sunlight and stimulates an explosion of microscopic ocean plant life (phytoplankton)
• Water cycles


  1. Evapotranspiration highest in summer months, lowest in winter months

  2. Large losses of precipitation to evapotranspiration, leading to exhaustion of soil moisture and lowest river flows in late summer

  3. Vegetation in summer means less runoff, more infiltration, and groundwater levels lowest in summer due to increased evaporation

  4. At higher latitudes, precipitation falls as snow at altitudes
• The last million years have been highly unstable with large fluctuations in global temperatures occurring at regular intervals
• Glacial periods


  1. More water transferred from ocean reservoir to storage in ice sheets and glaciers, sea levels lower by 100-130m

  2. Ice sheets and glaciers expand to cover continental land masses, less vegetation as glaciers extend over land

  3. Soil moisture freezes to create permafrost, less transpiration and lower humidity, less water percolates down to groundwater to recharge aquifers, slower water cycle as exchanges between stores reduced

  4. In the tropics, climates become drier with rainforests replaced by deserts and grasslands, lower evapotranspiration reduces exchanges of water with the oceans
• Interglacial periods


  Ice melts, warmer temperatures mean more evaporation, more vegetation stores more water in the biosphere, more transpiration and greater humidity, more water percolates to recharge aquifers
• Carbon cycle during glacial periods


  Less vegetation, lower temperatures and lower precipitation, reduced net primary productivity and photosynthesis, less plant matter to form soil carbon stores, freezing soil forms permafrost which reduces bacterial decomposition and respiration, reducing CO₂ and methane release, overall carbon pool in biosphere decreases as ecosystems change
• Carbon cycle during interglacial periods

  More photosynthesis due to warmer growing conditions leads to more plant matter forming greater soil carbon stores, CO₂ released from oceans as permafrost melts and organic matter decomposes, greater levels of CO₂ increasing by 100ppm
• Volcanoes kick-started life on the planet by outgassing CO₂ and other elements, and can produce CO₂ which warms the planet through the greenhouse effect, or produce ash and sulphur dioxide which blocks insolation from the sun and cools the planet
• Mount St Helens eruption produced 10,000,000 tonnes of CO₂, which is the same amount that humans produce every 2.5 minutes
• Wildfires


  1. Occur naturally in savannah grasslands, often triggered by lightning, combustion moves carbon from biomass into atmosphere, small amount moves into soil, stimulates more vigorous plant growth when ecosystem recovers and carbon is sequestered

  2. Humans reducing rainfall and increasing heat - wildfires more common in places they don't usually occur, forests less able to recover and re-sequester carbon from atmosphere due to decreased ability to photosynthesize
• Research and monitoring the Earth's life support systems is important