What is global warming or climate change?

Our planet is warming, and we are helping to make it happen by adding more heat-trapping gases, primarily carbon dioxide (CO2), to the atmosphere. The burning of fossil fuel (oil, coal, and natural gas) alone accounts for about 75 percent of annual CO2 emissions from human activities. Deforestation (the cutting and burning of forests that trap and store carbon) accounts for about another 20 percent.
The consensus among the scientific community continues to build. In a letter signed by 20 heads of scientific organizations, the following was stated in 2009:
Observations throughout the world make it clear that climate change is
occurring, and rigorous scientific research demonstrates that the
greenhouse gases emitted by human activities are the primary driver.
These conclusions are based on multiple independent lines of evidence,
and contrary assertions are inconsistent with an objective assessment of
the vast body of peer-reviewed science.
In 2011, Dr. Georges Benjamin, head of the American Public Health Association, stated, The science is unequivocal that global warming is occurring and that human activity is the cause of it. According to the head of the American Medical Association, extreme winter conditions and summer heat waves are both dangerous to health. There has been an increase in insect-borne diseasesdengue fever has been in Floridaand in air pollution; over 30 years, the asthma and allergy season has been extended by 20 days. A study by the University of New Hampshire has shown that the northeastern United States has warmed over the past hundred years, and that the rate of this warming is increasing over the past thirty years. According to the American Geophysical Union, which represents 41,000 scientists, Human activities are increasingly altering the Earth's climate?adding to natural influences.