Science, Technology and the Environment (SC NATS 1840A) –
Thursday, November 22 , 2012 nd
Is Atmospheric composition of Changing?
Accurate measurements of average CO c2ncentrations require isolated locations to avoid local
20% increase since 1960 confirmed by other stations
Seasonal cycle reflects northern growing season
Atmospheric methane has also increased
Little evidence of any increase in water vapour.
Why are GG Concentrations increasing?
Recent changes in greenhouse gas concentrations may be of man-made (anthropogenic) origin:
Conversion of forests to crop fields;
Wood & Fossil fuel combustion
Increased biological (decomposer) activity from landfill;
Larger cattle herds
Antarctic ice core measurements match up with period of industrialization
CO concentration increased by 40% since 1750
Methane concentration doubled since 1800
Attributing rise in GG concentration to human activities unambiguously is challenging
The story so far…
Greenhouse gas concentrations, which play a crucial role in determining Earth’s climate, are
Hypothesis: Global warming is caused by an enhanced greenhouse effect, the result of rising
atmospheric concentrations of greenhouse gases. Can this hypothesis be tested?
No simple experiment can establish a clear causal link between GG and climate change. We resort to
Mathematical models Mathematical Models (Climate Simulations):
General Circulation Model (GCM): mathematical representation of atmosphere + processes within it +
interaction with rest of ecosphere.
Provide insight into how different climate processes come together to yield aggregate behaviour.
Models divide atmosphere and surface into many grid cells
Equations describe processes within cells and between adjacent cells, and are solved
Simulation: Numerical experiment attempting to capture at least some aspect of reality.
Inputs: A GCM, Sun’s power output, initial conditions;
Variable: Atmospheric GG concentration over time;
Output: Long-term climate forecast.
Conclusions from GCMs:
Rising greenhouse gases can explain global warming:
A Doubling of CO 2oncentration by 2100 results in global average temperature increase
of about 3 degrees (range of 2 to 4.5 degrees) (IPCC ’07)
Projected Impacts (model-based):
Temperature and precipitation patterns;