Physical Impacts on the Carbon Cycle (AQA A Level Geography)

• Over the past 2.6 million years global climates have fluctuated between interglacial (warm) and glacial (cold) periods
• Data from Antarctic ice core samples, show temperatures and carbon dioxide levels roughly match 
• Higher temperatures are associated with high concentrations of carbon dioxide in the atmosphere
• The last 2.6 million years are the Quaternary period when there have been 60 cold periods and warmer interglacial periods
• The last ice age ended approximately 25,000 years ago

Ice core data: changes in temperature over the last 11,000 years

• An increase in carbon dioxide (CO2) in the atmosphere leads to enhanced global warming and temperature increase
• Lower levels of CO2 reduce the effectiveness of the natural greenhouse effect
• Increasing carbon dioxide levels increase global temperatures
• However, a change in temperature can also affect the levels of carbon dioxide in the atmosphere due to melting of the permafrost releasing methane (positive feedback loop)

• Cold conditions can affect weathering as cold water can hold more carbon dioxide but also freeze-thaw cycle increases exposing more rock to chemical weathering
• The extent and location of forests are affected by cold conditions - the treeline of the tundra
• Respiration and photosynthesis processes are reduced by cold conditions
• Carbon transfers to soil are reduced during cold conditions due to the reduced effectiveness of decomposers
• Less sediment is transported by rivers and deposited in seas and oceans as more water is stored as snow and ice
• Frozen soil stops the transfer of carbon

• Warmer temperatures increase the rate of decomposition which increases the rate of carbon transfer to the soil by decomposers
• Warm conditions melt the permafrost, so releasing carbon, along with other gases such as methane, stored in the permafrost 
• This further enhances the greenhouse effect which in turn, increases atmospheric warming
• This is an example of positive feedback, which further destabilises the system

Wildfires

• Burning transfers carbon from the biosphere to the atmosphere as CO₂
• This causes carbon emissions to spike in an already rising trend Extreme wildfires can turn vast areas from being carbon sinks to being a carbon source
• However, burning can encourage the growth of plants in the long term and some plants need wildfires to grow as it reduces competition for space
• As temperatures continue to increase, so does the risk of wildfires
• During 2019 a large area of tundra, covering Siberia, Alaska, Canada and Greenland experienced wildfires
• This contributed a significant amount of greenhouse gases into the atmosphere
• World Meteorological Organisation noted in July 2019 that:

Since the start of June we’ve seen unprecedented wildfires in the Arctic region. In June alone these wildfires (some the size of 100,000 football pitches) emitted 50 megatonnes of CO2 into the atmosphere, this is the equivalent of Sweden’s annual total CO2 emissions. This is more than was released by Arctic fires in the same month between 2010 and 2018 combined.

Volcanic Activity

• Carbon, stored in rocks for millions of years, is released, mainly as CO2 gas, to the atmosphere through volcanic eruptions
• During the Palaeozoic era, between 542 and 251 million years ago, volcanoes were more active than now  
• During this time, vast quantities of carbon dioxide were released into the atmosphere 
• Today, between 130 and 380 million tonnes of carbon dioxide is released annually through volcanic activity
• Compared to the 30 billion tonnes released by human activities such as burning fossil fuels is relatively low
• Therefore, volcanic activity contributes a relatively low percentage of CO2 to the overall carbon cycle
• However, volcanic activity can impact the carbon cycle through reducing photosynthesis rates, which will also have an impact on the water cycle e.g.:
  • The 1815 Indonesian Mt Tambora eruption, emitted sulphur dioxide gas, into the atmosphere
  • This reduced insolation and lowered global temperatures by 0.4 - 0.7°C in 1816