- Temperatures have risen by 1.4 degrees fahrenheit since the start of the 20th century, much of which has occurred in the last 30 years.
- Global mean surface temperatures are higher during the last few decades of the 20th century than during any comparable period since at least AD 1600.
Most scientists agree that this warming is primarily caused by human activities that have increased the amount of greenhouse gases in the atmosphere (H2O, CO2, CH4, N2O, O3). In fact, CO2 levels are at their highest in at least 650,000 years and continue to rise.
How do we know that human activities are changing the Earth's climate?
- There is a concurrent increase in surface temperature with CO2 and other greenhouse gases during the past century.
- Geographical pattern of observed warming with greater temperature increases over land and in polar regions than over the oceans.