Answer...
Some of the causes of increased CO(2) in the atmosphere include burning fossil fuels (like gasoline, diesel oil, coal). The combustion of these fuels produces carbon dioxide and oxides of nitrogen, among other gasses. Cutting down forest, ie. deforestation, and burning slash (releases CO2 directly and also reduces plants available to remove CO2 from atmosphere). Raising increasingly larger numbers of grazing animals like cows/sheep/horses which all release major amounts of methane into the atmosphere significantly increases atmospheric concentration of that gas. The cumulative affect of increased CO2 and CH4 in the atmosphere is that solar energy absorbed by the earth, when it is re-radiated into space, an increased amount of this re-radiated energy is trapped by gasses like CO2 and CH4 so the heat does not leave the earth but increases average surface temperature.
This increase in average surface temperature has a number of measurable and predicted affects, including:
• increasing photosynthesis rate (higher substrate concentration of CO2 for plants)
• changing climatic conditions may have the consequence of making some species which are highly adapted to a specific niche, extinct, as the conditions, to which they are adapted, change!
Further, specifically with respect to arctic ecosystem, increasing temperatures:
...cause melting of polar ice cap which will reduce habitat for some species like polar bears, making them less able to hunt on the ice (less ice) and harder for seals to birth and raise pups since they depend on leaving the pups on ice until they are weaned and can swim successfully in the water.
... cause melting of ice from polar ice cap and glaciers which may also increase mean sea level, flooding low lying coastal areas and killing people as well as making agricultural areas unsuitable when covered with salt water (which destroys ability of soil to raise plants because of high salt content).
... will permit soil normally frozen as permafrost to thaw which means increased detritus decomposition (more organic material to digest and warmer temperatures permitting bacteria and saprotrophs to survive, metabolize, grow and reproduce.
... will also permit temperate species, like spruce from boreal forests, to migrate further north as arctic temperatures cease having an arctic characteristic and, when warmer, are more like northern, temperate conditions. This would introduce new species to areas which they previously were prevented from
Further on arctic ecosystem:
melting of permafrost;
increased detritus decomposition;
expansion of temperate species / reduced range for arctic species;
example of an affected species;
examples of human activity;
more pests / pathogens;
disturbance to food chains / webs / trophic levels;