Secretary of Agriculture Tom Vilsack will have a big stack of mail waiting on his desk when he returns from the United Nations climate talks in Copenhagen, Denmark. Republican lawmakers have seized on Vilsack's comments earlier this week when he questioned USDA's own analysis and testimony on the impacts climate legislation will have on agriculture.

Responding to a question by venerable Reuters reporter Chuck Abbott in a conference call, Vilsack questioned the viability of his own department's analysis using what he considered outdated EPA data.

"Candidly I think there are other models more current and more complete that might lead to significantly and will lead to significantly different conclusions and we've already seen the impact of those models," Vilsack said.

Vilsack cited studies of the University of Tennessee and Kansas State University. He added the National Corn Growers Association will soon release a study as well "that talks about very little, if any, loss of crop land and negative impacts," he said. "It very much depends on where you start."

Sen. Mike Johanns, R-Neb., was the first to pounce. Johanns wrote Vilsack on Wednesday stating it was confusing after all of the testimony from USDA Chief Economist Joe Glauber two weeks ago that "you have called into question an analysis produced by your own department -- an analysis that has not even been made public yet, and that apparently took five months to produce."

Johanns went on, "I hope that after five months of working to produce a more in-depth analysis of cap-and-trade legislation, USDA's analysis is current and complete. Additionally, I hope the USDA analysis is robust enough to not be out of date even before it is released, and not be inferior to a university analysis that is over a month old. Your recent comments add some confusion to the picture. Any clarity you can provide regarding this matter would be greatly appreciated."

Can't you just feel the sarcasm oozing?

Well, Senate and House Agriculture Committee ranking Republicans didn't get their shots off as fast as Johanns but they too sent a letter Thursday to Vilsack on the topic. Sen. Saxby Chambliss, R-Ga., and Rep. Frank Lucas, R-Okla., penned a letter jointly.

"Statements that imply a lack of confidence in both the modeling used and work product developed by USDA and the Environmental Protection Agency (EPA) raise doubts regarding the Administration’s position on cap and trade legislation and, more importantly, the impacts on the agricultural and forestry sectors.

The Department’s testimony delivered earlier this month to the House Agriculture Committee is clear and unequivocal; agriculture will undergo significant structural impacts that will change how food, feed, fiber and fuel are produced in the United States. The disappearance of 59 million acres of cropland, higher food prices and lower exports will undoubtedly shape how farmers and ranchers make a living in the years ahead. While we can disagree on policy, we cannot ignore the facts when they are inconvenient to our preferred narrative.

In light of your critique of USDA’s analysis, we respectfully request your office consult with the EPA and report to the House and Senate Agriculture Committees on the problems with the economic model in order to reflect realistic scenarios while examining the impact of cap and trade on the agriculture and forestry sectors. Moving forward with flawed studies will only result in bad policy and legislation."

Republicans are coming to Glauber's defense because they loved everything he had to say. The notion that the big share of benefits would go directly to all the landowners who jump up and idle their land feeds right into the argument the GOP wants to hear on this topic.

But the Office of the Chief Economist ignored a lot of aspects of the debate. First, there was no analysis on what an renewable energy portfolio of 15 percent or 20 percent would do to drive the wind-energy sector. Where would those windmills be placed? Downtown Chicago outland Illinois, Kansas and North Dakota?

What would a renewable energy portfolio do to drive the selling of biomass to coal plants as well? USDA offers no explanation or understanding.

How does an increase in no-till practices translate into more organic matter in cropland? Does the increase in organic matter in the soil boost yields? One USDA scientist I know says so.

Could enrollment in a USDA conservation program such as the Conservation Stewardship Program fit into any effort to ensure land stay in forestry and pasture?

What would the loss of direct payments and other agricultural supports do to offset the chances a landowner would try to switch from cropland to forestry?

None of these questions are answered in the testimony two weeks ago, and I know none of these questions were asked by lawmakers when Glauber testified.

I can be found on Twitter at chrisclaytonDTN.