5.2 The greenhouse effect

Carbon Cycle

Concentrations of Carbon Dioxide

Relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect

Radiant energy of shorter-wave radiation from sun reaches earth (visible light and infra-red radiation), warms up sea and land.

When warmed, earth radiates infra-red (longer-wave radiation) back to space, but clouds and much is absorbed by gases in atmosphere.

Gases in atmosphere that absorb infra-red are called greenhouse gases.

Carbon dioxide; water vapor; methane; atmospheric pollutants - nitrous oxides, chlorofluorocarbons.

Nitrous oxides - waste product of combustion of fossil fuels, abundant source - exhaust fumes of internal combustion engines.

Levels of greenhouse gases correlated with global temperature.

Precautionary principle

If the effects of a human-induced changed would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect

We need to evaluate - most likely consequences that my result from failure to slow down the rising level of atmosphere carbon dioxide and then reduce it to earlier values; actions needed to deliver measures that enable us to achieve this.

Consequences of a global temperature rise on arctic ecosystems

Loss of ice habitats, leading to extensive flooding of surrounding low-lands, at least temporarily
Significant decay by microorganisms of the accumulated detritus, once released from its permafrost state, leading to huge releases into the atmosphere of methane and carbon dioxide, previously locked away in dead organic matter; this contributes to further global warming
An expansion in the range of habitats as significant quantities of soil rich in humus are formed
Appearance and growth of conifers, forming boreal forests (taiga); these areas absorb radiant heat energy from sunlight and contribute to further warming of the region, sine they replace ice, snow and frozen tundra
Appearance of insect-eating species, particularly of birds, able to take advantage of further increasing numbers of insects
A wider flora including annual plants typical of alpine meadows and grssland in summer seasons, where these appear
Appearance of small mammals such as the alpine marmot, able to take advantage of the expanding range of plant biota and habitats (in winter periods such mammals need to be able to retreat into excavated dens for group hibernation)
Predators for the expanded vertebrate populations, mostly birds of prey (raptors) that can fly on when winter returns
Increased presence of pathogens that parasites that expanded range of animal and plant life the changing habitat supports