The influence of human activities on the climate is clear and growing. If left unchecked, global warming will have an irreversible impact on people and ecosystems, says the UN's Intergovernmental Panel on Climate Change (IPCC) in its latest synthesis report. It calls for near-zero emissions of greenhouse gases by the end of the century
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| Climate change is real
The evidence
- Each of the last three decades has been successively warmer. 1983-2012 was the warmest 30-year period in 1,400 years in Northern Hemisphere
- Surface ocean (upper 75 metres) warmed by 0.11°C per decade between 1971 and 2010
- Since the beginning of industrial era, CO2 emissions have led to ocean acidification. The pH of its surface water has decreased by 0.1; acidity increased by 26%
- Greenland and Antarctic ice sheets lost mass at a higher rate between 2002 and 2011. Northern Hemisphere spring snow cover decreased in extent; glaciers shrunk worldwide
- Between 1979 and 2012, Arctic sea-ice extent decreased by 3.5-4.1% per decade; Antarctic sea-ice extent increased by 1.2-1.8% per decade. Antarctica witnessed strong regional differences, with sea-ice increasing in some regions and decreasing in others
- Mean sea level rose by 0.19 metre between 1901 and 2010. It is the highest rise in the last two millennia
- Limiting warming to less than 2°C relative to 1861- 1880 requires containing emissions to 2,900 Gt of CO2. Nearly 1,900 Gt of CO2 was emitted by 2011
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The projection
- Surface temperature is projected to rise in the 21st century under all possible scenarios. Heat waves will occur more often and last longer. Extreme rainfall events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level will continue to rise
- Such changes will obviously lead towards hotter climate. There will be more frequent hot and fewer cold temperature extremes on daily and seasonal time-scales as global mean surface temperature increases. Heat waves will occur with a higher frequency and longer duration. Occasional cold winter extremes will also continue to occur
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