Understanding Scientific Terms About Climate Change

The document clarifies that in science, uncertainty refers to the degree to which something is known rather than a complete lack of knowledge. It explains that climate scientists use specific probabilistic language—such as 'very likely' to denote a greater than 90 percent chance—to inform public policy and decision-making. While certain facts are established without uncertainty, such as the role of fossil fuels and the greenhouse effect in warming the Earth, uncertainties remain regarding the exact magnitude of future warming and the timing of specific ecological losses, often depending on future human actions to reduce emissions.

• In a scientific context, uncertainty is not defined as 'not knowing' but rather as a measure of 'how well something is known.' Scientists explicitly state levels of uncertainty to maintain transparency and prevent decision-makers from making critical errors, such as underestimating the height of a levee.
• Climate scientists use standardized language to communicate probability: a 'very likely' outcome indicates a probability greater than 90 percent, and 'very high confidence' indicates at least a 9 out of 10 chance of being correct.
• There is no scientific uncertainty regarding the fact that burning fossil fuels and clearing forests release carbon dioxide, that greenhouse gases trap heat via the greenhouse effect, and that the Earth is warming because these gases are released faster than natural processes can absorb them.
• Scientists have very high confidence that human-induced warming is affecting biological and physical systems globally, causing sea levels to rise, glaciers and permafrost to shrink, oceans to acidify, and plant and animal ranges to shift.
• Significant uncertainties remain regarding the exact amount of future global warming—estimated between 2.1 and 11 degrees Fahrenheit by 2100—and the timing of the disappearance of the ringed seal's summer sea ice habitat, with much of this uncertainty depending on human choices regarding emissions in the coming decade.

APA

Union of Concerned Scientists (2010). Understanding Scientific Terms About Climate Change. https://www.ucs.org/resources/understanding-scientific-terms-about-climate-change

Chicago

Union of Concerned Scientists. Understanding Scientific Terms About Climate Change. 2010. https://www.ucs.org/resources/understanding-scientific-terms-about-climate-change.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=Understanding Scientific Terms About Climate Change |date=19 March 2010 |url=https://www.ucs.org/resources/understanding-scientific-terms-about-climate-change |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2010understanding, author = {{Union of Concerned Scientists}}, title = {{Understanding Scientific Terms About Climate Change}}, institution = {Union of Concerned Scientists}, year = {2010}, month = mar, url = {https://www.ucs.org/resources/understanding-scientific-terms-about-climate-change}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }