In January 2005 Christopher Landsea resigned from work on the IPCC AR4, saying that it was "both being motivated by pre-conceived agendas and being scientifically unsound" because of Kevin Trenberth of the National Center for Atmospheric Research's idea that global warming was contributing to recent hurricane activity. Roger A. Pielke who published Landsea's letter writes: "How anyone can deny that political factors were everpresent in the negotiations isn't paying attention", but says that "Despite the pressures, on tropical cyclones they figured out a way to maintain consistency with the actual balance of opinion(s) in the community of relevant experts." He continues "So there might be a human contribution (and presumably this is just to the observed upwards trends observed in some basins, and not to downward trends observed in others, but this is unclear) but the human contribution itself has not been quantitatively assessed, yet the experts, using their judgment, expect it to be there. In plain English this is what is called a 'hypothesis' and not a 'conclusion.' And it is a fair representation of the issue."