Summary of main findings

• Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.
• A global assessment of data since 1970 has shown it is likely that anthropogenic warming has had a discernible influence on many physical and biological systems.
• Other effects of regional climate changes on natural and human environments are emerging, although many are difficult to discern due to adaptation and non-climatic drivers.
• More specific information is now available across a wide range of systems and sectors concerning the nature of future impacts, including for some fields not covered in previous assessments.
• More specific information is now available across the regions of the world concerning the nature of future impacts, including for some places not covered in previous assessments.
• Magnitudes of impact can now be estimated more systematically for a range of possible increases in global average temperature.
• Impacts due to altered frequencies and intensities of extreme weather, climate and sea-level events are very likely to change.
• Some large-scale climate events have the potential to cause very large impacts, especially after the 21st century.
• Impacts of climate change will vary regionally but, aggregated and discounted to the present, they are very likely to impose net annual costs which will increase over time as global temperatures increase.
• Some adaptation is occurring now, to observed and projected future climate change, but on a limited basis.
• Adaptation will be necessary to address impacts resulting from the warming which is already unavoidable due to past emissions.
• A wide array of adaptation options is available, but more extensive adaptation than is currently occurring is required to reduce vulnerability to future climate change. There are barriers, limits and costs, but these are not fully understood.
• Vulnerability to climate change can be exacerbated by the presence of other stresses.
• Future vulnerability depends not only on climate change but also on development pathway.
• Sustainable development can reduce vulnerability to climate change, and climate change could impede nations’ abilities to achieve sustainable development pathways.
• Many impacts can be avoided, reduced or delayed by mitigation.
• A portfolio of adaptation and mitigation measures can diminish the risks associated with climate change.