6.9 Flashcards
Why there is uncertainty in projections of future atmospheric CO2 concentrations
Physical Factors
Human Factors
Why there is uncertainty in projections of future atmospheric CO2 concentrations: Physical Factors
Oceans and forest act as carbon sinks and store heat. Oceans take decades to respond to changes in greenhouse gas concentrations.
Response to higher levels of greenhouse gases and higher temp continue to affect global climate for possibly hundreds of years
Why there is uncertainty in projections of future atmospheric CO2 concentrations: Human Factors
Population Change
Increasing affluence in energy consumers by 2050 - with spending power equal to USA. Changing diets and increased mobility mean more emissions.
Energy sources
Energy consumption grew by 2% between 2008 and 2014. However, renewable sources made up 2/3 of increase in electricity production in 2015
Positive feedback mechanisms to projections of future atmospheric concentrations
Permafrost
Peatlands
Positive feedback mechanisms to projections of future atmospheric concentrations: Permafrost
When permafrost melts, releases trapped carbon into atmosphere as CO2 and methane - increasing atmospheric greenhouse gas concentrations and leading to increased temp and melting
FURTHERMORE Reduced reflection (albedo) of solar radiation by Earth’s surface as snow and ice melt, with darker surfaces absorbing more heat energy, and methane releases
Positive feedback mechanisms to projections of future atmospheric concentrations: Peatlands
Warming causes peat to dry out as water tables fall, aw well as increasing rate of decomposition
Peatlands tend to emit carbon in form of methane, increasing concentration of greenhouse gases
Negative feedback mechanisms to projections of future atmospheric concentrations
Increased plant growth as result of higher CO2 concentrations
Increase in cloud cover due to higher evaporation rates which would reflect solar energy
Projections of future atmospheric concentrations: Tipping points
In 2014, IPCC defined a ‘tipping point’ as an abrupt, possibly irreversible, large-scale change over a few decades or less.
IPCC identified seven possible tipping points:
Forest dieback
Atlantic thermohaline circulation collapse
Projections of future atmospheric concentrations: Tipping points (Forest dieback)
TROPICAL RAINFOREST
Rainfall in Amazon Basin is largely recycled from moisture within forest. Rainforest is subject to drought, causing tree die back. Tipping point could be reached, where level of die back actually stops recycling of moisture within rainforest - resulting in further die back
BOREAL FOREST
Forest is subject to drought, causing tree die back. Tipping point could be reached where trees no longer absorb enough CO2 from atmosphere, leading to increased leves of greenhouse gases.
Projections of future atmospheric concentrations: Tipping points (Atlantic thermohaline circulation collapse)
To keep ‘conveyor belt’ of warm water heading from Tropics towards Britain, heavy, salty water must sink in the north.
However, melting of northern ice sheets releases significant quantities of freshwater into ocean, which is lighter and less salty — thus blocking and slowing conveyor belt. As ice sheets melt, ocean circulation is susceptible to a critical tipping point.
