The widespread species impacts observed to date highlight the major biodiversity impacts associated with projected distribution of novel and disappearing climates by 2100, including current biodiversity hotspot regions. Increasingly severe impacts are certain, and are likely to include disruption and collapse of food webs (e.g. from changes in plankton abundance). Increases in extreme weather events such as hurricanes, droughts and floods will increase the vulnerability of many species. Even relatively modest additional temperature increases are sufficient to compromise many reptiles – along with some bird and fish species – whose sex is temperature-determined. Higher temperatures can increasingly result in feminisation of populations of a wide range of species, compromising breeding success. Extremes in temperature will also affect many species, especially freshwater species, as they are more restricted in their movement and the smaller water bodies they inhabit heat up more rapidly. Species reliant on low-lying coastal habitats, including many migratory species and important fisheries species, will be severely compromised as sea level rise and other environmental stressors affect their viability. Ocean acidification will increasingly directly and indirectly impact a wide range of species reliant on aragonite and calcite concentrations, including corals, molluscs and krill, with serious consequences for entire ecosystems.
The combination of climate system inertia and the fact that fossil fuel emissions are still tracking IPCC’s high emissions trajectory scenario greatly increases the risk of climate-change driven ‘tipping points’ for major systems. These include the Greenland ice-sheet melt, dieback of the Amazon rainforest and shift of the West African monsoon. Such regional tipping-point sensitivities, and their amplifying feedback risks, need to be taken into account when defining the level of dangerous anthropogenic interference with the climate system. It is the scientific rationale for considering 350 ppm CO2 as the safe planetary boundary for climate change.