It is safe to say human interference has had a great affect on global warming. According to the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), global surface temperature increased by 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 20th century. Most of the observed temperature increase since the middle of the 20th century has been caused by increasing concentrations of greenhouse gases, which result from human activities such as the burning of fossil fuel and deforestation. Global dimming, a reduction of sunlight reaching the surface as a result of increasing atmospheric concentrations of human-made particulates, has partially countered the effects of warming induced by greenhouse gases.
The case for attributing the recent global warming to human activities rests on the following undisputed scientific facts:
- Carbon dioxide (CO2) is a greenhouse gas that warms the atmosphere.
- Since pre-industrial times, atmospheric CO2 concentrations have increased from about 280 parts per million (ppm) to over 380 ppm. Current concentrations of CO2 and other greenhouse gases are unprecedented in at least the last 650,000 years, based on records from gas bubbles trapped in polar ice.
- Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique "fingerprint.”
- Since pre-industrial times, global average temperatures have increased by about 0.7 degrees C, with about half of the warming occurring over the past few decades.
- The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases.
- The U.S. National Academy of Sciences, the independent organisation of the country’s most renowned scientists established by Congress to advise the nation on scientific and technical issues, has concluded: "The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action.”
The case for attributing the recent global warming to human activities rests on the following undisputed scientific facts:
- Carbon dioxide (CO2) is a greenhouse gas that warms the atmosphere.
- Since pre-industrial times, atmospheric CO2 concentrations have increased from about 280 parts per million (ppm) to over 380 ppm. Current concentrations of CO2 and other greenhouse gases are unprecedented in at least the last 650,000 years, based on records from gas bubbles trapped in polar ice.
- Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique "fingerprint.”
- Since pre-industrial times, global average temperatures have increased by about 0.7 degrees C, with about half of the warming occurring over the past few decades.
- The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases.
- The U.S. National Academy of Sciences, the independent organisation of the country’s most renowned scientists established by Congress to advise the nation on scientific and technical issues, has concluded: "The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action.”
