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

Natural Climate Change & Carbon Cycle

• 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

• 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)

Impacts of Cold & Warm Conditions

• 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

Impacts of Wildfires & Volcanic Activity

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:

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