The present global biota has been affected by fluctuating Pleistocene (last 1.8 million years) concentrations of atmospheric carbon dioxide, temperature, and precipitation, and has coped through evolutionary changes, species plasticity, range movements, and/or the ability to survive in small patches of favourable habitat (refugia). These changes, however, occurred in a landscape that was not as fragmented as it is today and with little or no additional pressure from human activities.

Habitat fragmentation has confined many species to relatively small areas within their previous ranges, resulting in reduced genetic variability. Warming beyond the ceiling of temperatures reached during the Pleistocene will stress ecosystems and their biodiversity far beyond the levels imposed by the global climatic change that occurred in the recent evolutionary past.

Current rates and magnitude of species extinction far exceed normal background rates. Human activities have already resulted in the loss of biodiversity and thus may have affected goods and services crucial for human well-being. The rate and magnitude of climate change induced by increased greenhouse gas emissions has and will continue to affect biodiversity either directly or in combination with other drivers of change.