Are Humans Responsible for Global Warming?
Are Humans Responsible for Global Warming?
A REVIEW OF THE FACTS
APRIL 2007
AUTHORS
James Wang, Ph.D. Bill Chameides, Ph.D.
Are Humans Responsible for Global Warming?
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 0.7ºC, 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 organization 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.” Some argue that the recent global warming is due to natural fluctuations and not to human activities. This argument and its fallacies are discussed below.
Argument 1: CO2 is not coming from human activities
CO2 has natural sources: volcanoes for example. All animals exhale it. How can human activities be affecting the concentration of CO2 on a global scale?
The Facts
Natural processes emit large quantities of CO2 into the atmosphere, but they also
A REVIEW OF THE FACTS
APRIL 2007
AUTHORS
James Wang, Ph.D. Bill Chameides, Ph.D.
Are Humans Responsible for Global Warming?
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 0.7ºC, 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 organization 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.” Some argue that the recent global warming is due to natural fluctuations and not to human activities. This argument and its fallacies are discussed below.
Argument 1: CO2 is not coming from human activities
CO2 has natural sources: volcanoes for example. All animals exhale it. How can human activities be affecting the concentration of CO2 on a global scale?
The Facts
Natural processes emit large quantities of CO2 into the atmosphere, but they also