Below is a key statement from the report published by the Australian Academy of Science:
Although climate varies from year to year and decade to decade, the overall upward trend of average global temperature over the last century is clear. Climate models, together with physical principles and knowledge of past variations, tell us that, unless greenhouse gas emissions are reduced and greenhouse gas concentrations in the atmosphere are stabilised, global warming will continue.
Climate models estimate that, by 2100, the average global temperature will be between 2°C and 7°C higher than pre-industrial temperatures, depending on future greenhouse gas emissions and on the ways that models represent the sensitivity of climate to small disturbances. Models also estimate that this climate change will continue well after 2100.
A 2°C global warming would lead to a significantly different world from the one we now inhabit. Likely consequences would include more heat waves, fewer cold spells, changes to rainfall patterns and a higher global average rainfall, higher plant productivity in some places but decreases in others, disturbances to marine and terrestrial ecosystems and biodiversity, disruption to food production in some regions, rising sea levels, and decreases in Arctic ice cover. While aspects of these changes may be beneficial in some regions, the overall impacts are likely to be negative under the present structure of global society.
A warming of 7°C would greatly transform the world from the one we now inhabit, with all of the above impacts being very much larger. Such a large and rapid change in climate would likely be beyond the adaptive capacity of many societies and species.
The report can be accessed here: http://www.science.org.au/policy/climatechange.html