11.3 greenhouse gases
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what are the main greenhouse gases in the earth’s atmosphere
carbon dioxide, methane, water vapour
does all of the energy reaching the earth warm the planet
no, almost 30% is reflected back into space from the atmosphere and surface
what kind of radiation do greenhouse gases let pass through
• short-wavelength electromagnetic radiation • such as ultraviolet light
what kind of radiation do greenhouse gases absorb
• longer-wavelength radiation • the earth cools down by emitting infrared (thermal) radiation • greenhouse gases absorb infrared radiation
what does radiation do to molecules
stimulates the bonds in these molecules to vibrate, bend and stretch more vigorously, raising their temperature
the higher the proportion of greenhouse gases in the air…
…the more energy is absorbed
equation for burning of propane (CO2 released from burning fossil fuel)
C3H8 + 5O2 –> 3CO2 + 4H2O
how does methane get into the atmosphere
• swamps and rice fields • grazing cattle and their decomposing waste • increase in population –> more landfill sites –> source of methane
what human activities affect the balance of co2 absorbed and co2 produced
• TRF deforestation • co2 removed from the air as trees photosynthesise is reduced • as the temperature rises, co2 gets less and less soluble in water • this makes the oceans less effective as co2 sinks
what do a minority of scientists believe about climate change
rises observed are due to natural variations that have always happened throughout the long history of the earth
how do scientists search for evidence for climate change
linking the evidence between the levels of co2 and climate
what is a source of carbon dioxide
• ice cores drilled from Greenland’s ice sheet, which have gases trapped inside • scientists can analyse the trapped air to find how the composition of gases in the atmosphere has changed over time
can you predict the effect of increasing levels of carbon dioxide
no