Key conclusions from the 1st IPCC volume report “Climate Change 2007”, The Physical Science Basis
- Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising sea level.
- It is “very likely” that increases in man-made greenhouse gas emissions have caused most of the rise in globally averaged temperatures since the middle of the 20th century. It is “extremely unlikely” that this warming was due to natural climate variability alone.
- During the last 100 years the Earth has warmed by 0.76°C on average, and the rate of warming has further increased. The 11 warmest years on record have all occurred in the last 12 years. The second half of the 20th century was the warmest period in the northern hemisphere for at least 1,300 years. Europe has warmed by about 1°C over the past 100 years, faster than the global average.
- Based on scenarios that assume no further action is taken to limit emissions, the best estimates of the projected further rise in the global average temperature by 2100 range from 1.8 to 4.0°C The full uncertainty range for projected global warming this century is 1.1-6.4°C .
- Rates of observed sea level rise almost doubled from 18 centimetres per century in 1961-2003 to 31 cm per century in 1993-2003.
- The concentration of carbon dioxide (CO2) and other greenhouse gases in the atmosphere has continued to increase due to man-made emissions, and the rate of increase has further accelerated. Current concentrations of CO2 and methane are the highest for at least 650,000 years.
- New research indicates that plants and soils will absorb less CO2 as the world warms. Hence, a larger fraction of the CO2 emitted will remain in the atmosphere, and the magnitude of climate change caused by a given level of emissions will be larger than previously thought.
- Extreme weather events have increased and regional climate patterns are changing. Heat waves and other weather extremes, as well as changes in atmospheric circulation patterns, storm tracks and precipitation, can now be traced back to climate change caused by human activities.
- Scientists have improved their ability to predict future climate change. Confidence in regional climate change projections has increased due to better models and more powerful computers. The temperature over land and at high northern latitudes will be higher than the global average. In the Arctic it could be on average 6°C - and possibly as much as 8°C - warmer by the end of this century than at the end of the 20th.
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