4.4 Climate Change Flashcards
The Earth is kept much warmer by gases in the atmosphere that retain heat. These gases are referred to as
greenhouses gases.
The greenhouse gases that have the largest warming effect on the Earth are:
carbon dioxide (cell respiration, burning fossil fuels)
water vapour (evaporation, transpiration)
Other gases including methane and nitrogen oxides have less impact:
methane (marshes, organic landfill sites, extraction of fossil fuels)
nitrogen oxides (naturally by bacteria, agriculture, vehicle exhausts)
Why is the surface of the Earth warmer at night if there is cloud cover?
The water droplets in clouds retain heat during the day and at night re-radiate the heat back to the surface
Why is the surface of the Earth cooler when there is more cloud coverage?
The water droplets in clouds reflect a range of different wavelengths of radiation in both directions (including radiation coming inward that would have been re-emitted as heat*).
*Although clouds make the surface of the Earth cooler in the short term. They do not stop the greenhouse effect, it is just delayed or slowed down.
impact of a greenhouse gas
Ability to absorb longwave radiation
(especially infrared/heat)
- Methane has 33 times the effect of CO2 (but is not very abundant)
concentration in the atmosphere
- rate of release
- persistence
- Water vapour enters the atmosphere very rapidly, but only remains for days whereas methane persists for 12 years, and CO2 persists for even longer.
How the greenhouse effect works
- ~25% of solar radiation is absorbed by the atmosphere. Most is UV light absorbed by ozone.
- ~75% of solar radiation penetrates the atmosphere and reaches the Earth’s surface.
- The surface of the Earth absorbs short-wave solar energy and releases it at longer wavelengths (as heat).
- Up to 85%* of released heat is captured by greenhouse gases in the atmosphere and remitted in all directions.
- Some re-emitted heat passes back to the surface of the Earth, causing warming
How the greenhouse effect works
- ~25% of solar radiation is absorbed by the atmosphere. Most is UV light absorbed by ozone.
- ~75% of solar radiation penetrates the atmosphere and reaches the Earth’s surface.
- The surface of the Earth absorbs short-wave solar energy and releases it at longer wavelengths (as heat).
- Up to 85%* of released heat is captured by greenhouse gases in the atmosphere and remitted in all directions.
- Some re-emitted heat passes back to the surface of the Earth, causing warming
ice cores
To deduce historic carbon dioxide concentrations and temperatures ice cores are drilled in Antarctic ice sheets
Vostock ice core (pictured) drilled at a Russian monitoring station in East Antarctica is an example of an ice core.
A cylinder of ice was collected by drilling from to the bottom of the Antarctic ice sheet. The total length of the core was 2083 meters.
The core shows annual layers, which can be used to date the air bubbles trapped in the ice.
Analysis of the gas content of the bubbles gives both the concentration of CO2 in the atmosphere and the air temperature (from oxygen isotopes) at the time ice was formed.
Evidence for a correlation between atmospheric carbon dioxide (CO2) and average global temperatures
The correlation is supported by ice core data over the last 800,000 years
Temperature shows greater variation than CO2
Most, but not all rises and falls in CO2 have correlated with temperature rises and falls
The same trend has been found in other ice cores.
In the absence of greenhouse gases, the Earth would be much colder…
If concentration of GHGs increased, more heat would be retained and global temperatures would rise
However, global average temperatures are not directly proportional to greenhouse gas concentrations.
Other factors, e.g. sun spot activity, have an impact global average temperatures
Increases in greenhouse gas concentrations will likely cause:
higher global average temperatures
more frequent and intense heat waves
some areas becoming more prone to droughts
more evaporation of water from oceans
some areas more prone to intense periods of rainfall and flooding
tropical storms to be more frequent and more powerful
changes to ocean currents, e.g. weakening of the Gulf Stream would mean colder temperatures in north-west Europe
The link between human emissions and atmospheric levels of CO2
Historically, fluctuations of CO2 range from 180-300 ppm
In recent times, CO2 levels are nearing 400 ppm
Industrial Revolution marks a huge increase in CO2 levels
- combustion of coal, oil and natural gas
key points
There is a strong correlation between human emissions and atmospheric levels of CO2
As atmospheric CO2 levels have increased the amount of CO2 absorbed by carbon sinks has increased (only about 40% of emissions have remained in the atmosphere)
Ocean acidification – the causes and effects
The ocean absorbs about 25% of the CO2 emitted into the atmosphere. Therefore as atmospheric CO2 increases so do the levels in the ocean.
Since 1800 the pH of seawater* has fallen by 0.1 pH units. Since the pH scale is logarithmic, this represents approx. a 30% increase in acidity.
Estimates of future CO2 levels, indicate that by 2100 seawater could be nearly 150% more acidic (a further decrease of 0.5 pH) to a level not seen for more than 20 million years.
When CO2 dissolves in water it forms a variety of molecules:
dissolved free CO2
carbonic acid (H2CO3)
bicarbonate (HCO−3)
carbonate (CO32−)
