4.4 - Climate Change Flashcards
Essential idea:
Essential idea: Concentrations of gases in the atmosphere affect climates experienced at the Earth’s surface.
- 4.U1 Carbon dioxide and water vapour are the most significant greenhouse gases.
- 4.U2 Other gases including methane and nitrogen oxides have less impact.
The Earth is kept warm 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 (below)
water vapour (e.g. clouds)
Other gases including methane and nitrogen oxides have less impact.
nitrogen oxides are released naturally by bacteria in some habitats and also by agriculture and vehicle exhausts.
Greenhouse gases together make up less than 1% of the atmosphere.
Q – 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
Q – why is the surface of the Earth cooler during the day 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*).
impact of a greenhouse gas
Ability to absorb long-wave radiation
(especially infrared/heat)
Methane has 33 times the effect of CO2 (but is not very abundant)
abundance in the atmosphere
CO2 is very abundant making up 400 ppm by volume of the atmosphere (0.04%)
rate of release + persistance
Water vapour enters the atmosphere very rapidly, but only remains for days whereas CO2 persists for years.
How the greenhouse effect works
≅25% of solar radiation is absorbed by the atmosphere.
≅75% of solar radiation penetrates the atmosphere and reaches the Earth’s surface.
The surface of the Earth absorbs short-wave solar energy and re-emits at longer wavelengths (as heat).
Up to 85%* of re-emitted heat is captured by greenhouse gases in the atmosphere.
Heat passes back to the surface of the Earth, causing warming
If the Earth had no atmosphere, and hence no greenhouse effect, the average surface temperature would be approx. -18oC. Suggest the impact to life on Earth if this occurred.
Evidence for a correlation between atmospheric carbon dioxide (CO2) and average global temperatures
Key points
Global temperatures show large variations (for various reasons)
(despite this) there is strong support for correlation between atmospheric carbon dioxide and increase in global temperatures
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 carbon dioxide 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
2
Key points
The correlation is supported by ice core data over the last 400,000 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.
Correlation does not prove causation, but in this case we know from other research that carbon dioxide is a greenhouse gas.
The link between human emissions and atmospheric levels of CO2
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)
anthropogenic = human caused
4.4.U6 Global temperatures and climate patterns are influenced by concentrations of greenhouse gases.
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
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
4.4.A1 Threats to coral reefs from increasing concentrations of dissolved carbon dioxide.
Research indicates that, by 2100 coral reefs may erode faster than they can be rebuilt
This could compromise the viability of these ecosystems and the (estimated) one million species that depend on coral reef habitat
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.
Ocean acidification – the causes and effects 2
When CO2 dissolves in water it forms a variety of molecules:
Dissolved free CO2
Carbonic acid (H2CO3)
Bicarbonate (HCO3−)
Carbonate (CO32−)
It is not just the creation of carbonic acid that affects pH; when bicarbonate and carbonate ions are formed H+ ions are released thus decreasing the pH of seawater
at risk vs benefit
Carbonate ions are not very soluble, therefore the concentration in seawater is low. Dissolved CO2 decreases the carbonate concentration further.
Marine calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.*
Need to absorb carbonate ions from seawater to make the calcium carbonate in their skeletons.
Photosynthetic algae and sea grasses
Low CO2 is a limiting factor for photosynthesis
pteropod
The pteropod is a tiny sea creature about the size of a small pea. Pteropods are a major food source for many animals including North Pacific juvenile salmon. The photos below show what happens to a pteropod’s shell when placed in sea water with pH and carbonate levels projected for the year 2100.
