The trends in atmospheric gases are studied as indicators of potential climate change.
Atmospheric carbon dioxide has been monitored at Mauna Loa atmospheric laboratory on Hawaii since 1958. There are now other laboratories around the world which are adding to the database of carbon dioxide levels in the atmosphere. The data can be accessed at The Carbon Dioxide Information Center, Department of Energy, USA by searching 'Trace Gas Measurements'.
The following slide shows a graphic from that web site.
Carbon dioxide is released unevenly around the world which is in part due to the distribution of vegetation. The collective data therefore allows us to see what happened after there is a mixing of the atmospheric carbon dioxide.
The analysis of carbon dioxide trends is complex and is affected by a number of factors and assumptions.
However the basic trend is an increase in atmospheric carbon dioxide levels.
Longer term estimates of global CO 2 levels have been determined by a variety of sources including the gases trapped in ancient ice cores.
The greenhouse effect is a natural process that creates moderate temperatures on earth to which life has adapted. The earth has relatively little carbon dioxide in its atmosphere compared to a planet like Venus, which has an atmosphere of CO 2 that is 200, 000 times greater and a surface temperature nearly twenty times higher than earth.
The enhanced greenhouse effect is the concerned that the activities of may be increasing the levels of carbon dioxide and other 'greenhouse gases' such as methane and oxides of nitrogen in the atmosphere. That this may lead to increased global temperatures and climate change.
The precautionary principle holds that, if the effects of a human-induced change 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.
Effects include increased rates of decomposition of detritus previously trapped in permafrost, expansion of the range of habitats available to temperate species, loss of ice habitat, changes in distribution of prey species affecting higher trophic levels, and increased success of pest species, including pathogens.