English: This diagram shows some of the main impacts of global warming. This is a draft image for discussion on Talk:Effects of global warming. Impacts are organized into 4 categories: (1) Physical systems, (2) ecological systems, (3) social systems; and (4) abrupt and large-scale changes. The shaded bars indicate the level of risk associated with different magnitudes of global warming. The following scale is used:

• White shading: no detectable risk
• Light grey: small risk
• Medium grey: moderate risk
• Dark grey: large risk
• Black: severe risk

Risks apply to observed and projected climate change. Later text explains whether observed risks are attributable to climate change or due to climate variability. Some risks are given based on (1) current adaptation (c.a.) practices to climate variability and change, and (2) for a hypothesized highly adapted state (h.a.). Global temperatures are measured relative to pre-industrial times, approximated as the years 1850 to 1900. Recent times are taken as 2003 to 2012.

Physical systems

• Increase in risk associated with some extreme weather events: small to moderate risk at present; large risk starting around 1.6 °C.
• Other effects of global warming include global mean sea level rise and ocean acidification. Global warming could be irreversible for several millennia.

Ecological systems

• Climate change is a significant risk for some ecosystems and organisms, e.g., Arctic ecosystems and coral reefs: Moderate risk at present; large risk from 1.6 °C; severe risk from 2.6 °C.
• Risk of widespread extinctions: Small at present; moderate at 2 °C; large at 4 °C.

Social systems

• Sectors affected include food security, water resources and human health. Impacts will be uneven within and across different countries. Climate change increases the risk of many negative impacts, but there will be some positive effects.
• Africa: Risks associated with reduced crop productivity: Present: Moderate (c.a.) or low (h.a.) risk from climate variability; 2 °C: high (c.a.) or moderate (h.a); 4 °C: very high (c.a. and h.a.)
• North America: Risks associated with urban flooding in riverine and coastal areas: Present: Moderate (c.a.) or low (h.a.) risk from climate variability; 2 °C: moderate (c.a. and h.a); 4 °C: high (c.a. and h.a.).

Abrupt and large-scale changes

Climate change can lead to abrupt and large-scale changes in natural and human systems. The risk of these changes increases with temperature.

• Declines in late-summer Arctic sea ice extent: Present: low to moderate risk; 2 °C moderate to large risk; 4 °C: severe risk.
• Sustained global warming could lead to the near-complete loss of the Greenland ice sheet over a millennium or more, which would result in global mean sea level rise of about 7 m: risk is low at 1 to 2 °C; moderate at 3 °C, and large at 4 °C and above.

Notes

Sources are: Working Group's I and II (WG1 and 2) contributions to the Intergovernmental Panel on Climate Change 5th Assessment Report (IPCC AR5, 2013 and 2014); and the US National Research Council (US NRC, 2013) report "Abrupt Impacts of Climate Change: Anticipating Surprises". Details:

• IPCC AR5 WG1 references [1] (archive url): Summary for Policymakers
• IPCC AR5 WG2 references [2] (archive url): Summary for Policymakers; Technical Summary; Chapter 19.
• US NRC [3] (archive url)