What’s the difference between “global warming” and “climate change”?
“Global warming” refers to the increase of the Earth’s average surface temperature due to a build-up of greenhouse gases in the atmosphere. “Climate change” is a broader term that includes many other impacts resulting from global warming (for example., changes in precipitation and ocean acidity) and different geographic scales (for example, a continent, an ocean, a hemisphere, the planet).
Are scientists in agreement about the reality and cause of climate change?
Yes. Polls of climate scientists show there is no “debate” within the field. For example, this study shows that 97 percent of science papers addressing climate change support the consensus that humans are causing global warming.
Many issues related to climate change require further study. How fast will the ice sheets melt? How are changes in the jet stream related to climate change? But scientists agree that the planet is warming, and that human activities are the primary cause.
Is climate change a natural or human-caused phenomenon?
Human activities that release carbon dioxide and other greenhouse gases into the atmosphere are largely responsible for the climate change observed over the last century. The pattern of warming that we have observed, in which warming has occurred in the lower portions of the atmosphere (the troposphere) and cooling has occurred at higher levels (the stratosphere), is consistent with how greenhouse gases work – and inconsistent with other factors that can affect the global temperature over many decades, like changes in the sun’s energy.
While it is true that the climate has changed throughout all of Earth’s history as a result of natural forces (like volcanic eruptions and variations in the sun’s energy), the current situation is very different. Natural forces alone cannot account for the warming that has occurred, and the pace of warming is unique in Earth history.
The congressionally-mandated National Climate Assessment summarizes the state of our knowledge:
Evidence for climate change abounds, from the top of the atmosphere to the depths of the oceans. Scientists and engineers from around the world have meticulously collected this evidence, using satellites and networks of weather balloons, thermometers, buoys, and other observing systems. Evidence of climate change is also visible in the observed and measured changes in location and behavior of species and functioning of ecosystems. Taken together, this evidence tells an unambiguous story: the planet is warming, and over the last half century, this warming has been driven primarily by human activity.
How much warmer will the Earth get?
Projections for the likely increase in average global temperature this century range from about 2°F to around 11°F compared to temperatures in the late 1900s. However, at the higher latitudes, many locations are likely to warm by more than the global average (see figure).
The large range among projections stems mostly from uncertainty about future energy use and greenhouse gas emissions. To keep warming to the lower end of the range, significant cuts in emissions would need to be implemented starting now. Greenhouse gas emissions trends in recent decades correspond much more closely to the high end of the warming projections.