Although mass media continue to play a key role in translating scientific uncertainty for public discourse, communicators of climate science are becoming increasingly aware of their own role in shaping scientific messages in the news. As an example of how future media research can provide relevant feedback to climate communicators, the present study examines the ways in which grammatical and word choices represent and construct uncertainty in news reporting about the Intergovernmental Panel on Climate Change (IPCC). Qualifying and hedging language and other "epistemic markers" are analyzed in four newspapers during 2001 and 2007: the New York Times and Wall Street Journal from the USA and El País and El Mundo from Spain. Though the US newspapers contained a higher density of epistemic markers and used more ambiguous grammatical constructs of uncertainty than the Spanish newspapers, all four media sources chose similar words when questioning the certainty around climate change. Moreover, the density of epistemic markers in each newspaper either remained the same or increased with time, despite ever-growing scientific agreement that human activities modify global climate. While the US newspapers increasingly adopted IPCC language to describe climate uncertainties, they also exhibited an emerging tendency to construct uncertainty by highlighting differences between IPCC reports or between scientific predictions and observations. The analysis thus helps identify articulations of uncertainty that will shape future media portrayals of climate science across varying cultural and national contexts.