More than 50 California-based scientists are among those who signed a letter protesting “McCarthy-like” attacks on climate scientists in the United States.

The letter, circulated as a kind of petition to selected members of the National Academy of Sciences (NAS), is both a defense of established climate science and a counter-offensive against an increasingly vocal community that rejects that science and some of the proposed policy responses. The letter asserts that the signatories are “deeply disturbed by the recent escalation of political assaults on scientists in general and on climate scientists in particular.”

Steering the core group of scientists behind the letter (full text and list of signatories available as a PDF download) was Peter Gleick, who heads the Pacific Institute in Oakland. Gleick, whose primary focus is on water policy issues, has been an outspoken defender of the prevailing climate science and has, on occasion, answered critics on this blog. Gleick declines credit as the sole author, saying it was written by a group of a half-dozen co-authors.

Other excerpts:

“Many recent assaults on climate science and, more disturbingly, on climate scientists by climate change deniers, are typically driven by special interests or dogma, not by an honest effort to provide an alternative theory that credibly satisfies the evidence.”

“The Intergovernmental Panel on Climate Change (IPCC) and other scientific assessments of climate change, which involve thousands of scientists producing massive and comprehensive reports, have, quite expectedly and normally, made some mistakes. When errors are pointed out, they are corrected. But there is nothing remotely identified in the recent events that changes the fundamental conclusions about climate change…”

The letter concludes by calling for “an end to McCarthy- like threats of criminal prosecution against our colleagues based on innuendo and guilt by association, the harassment of scientists by politicians seeking distractions to avoid taking action, and the outright lies being spread about them.”

A total of 255 scientists signed the letter, which was published this week in the journal Science (available by subscription only). High-profile signers include Paul Ehrlich and Stephen Schneider, both based at Stanford.

Perhaps just as interesting as who signed the letter is who did not. Missing are several luminaries in California climate science circles, such as Dan Cayan and Richard Somerville of the Scripps Institution, and Ben Santer at Lawrence Livermore National Lab. Santer has participated in media calls organized to defend findings of the IPCC. Santer has served as an IPCC lead author.

Gleick explained to me that the letter was circulated only to NAS members listed in climate-related disciplines. From a check of the proprietary NAS member database, it appears that Cayan and Santer are not members. Also missing from the signatories is Stanford’s Chris Field, who is engaged in preparing the next IPCC report. Field has been an NAS member since 2001.

According to Gleick, a few declined to sign as they were “involved in ongoing assessments” for NAS when the letter was circulated and wished to avoid any apparent conflicts of interest. Gleick admits that scientists walk a precarious line when they cross over from research into activism, but says sometimes it’s justified. “It’s important that scientists speak out when an issue is as important as climate is,” he said.