The National Center for Science Education describes climate change denial as disputing differing points in the scientific consensus, a sequential range of arguments from denying the occurrence of climate change, accepting that but denying any significant human contribution, accepting these but denying scientific findings on how this would affect nature and human society, to accepting all these but denying that humans can mitigate or reduce the problems. James L. Powell provides a more extended list,'The earth is not warming.''All right, it is warming but the Sun is the cause.''Well then, humans are the cause, but it doesn't matter, because it warming will do no harm. More carbon dioxide will actually be beneficial. More crops will grow.''Admittedly, global warming could turn out to be harmful, but we can do nothing about it.''Sure, we could do something about global warming, but the cost would be too great. We have more pressing problems here and now, like AIDS and poverty.''We might be able to afford to do something to address global warming some-day, but we need to wait for sound science, new technologies, and geoengineering.''The earth is not warming. Global warming ended in 1998; it was never a crisis.'</ref> as does climatologist Michael E. Mann in "six stages of denial", a ladder model whereby deniers have over time conceded acceptance of points, while retreating to a position which still rejects the mainstream consensus: