The U.S. Senate version of comprehensive climate legislation is a mystery wrapped in an enigma. Senate Majority Leader Harry Reid (D-NV) says his chamber will focus on the issue once it's finished with financial reform, but the recent surge of interest in immigration reform may push it to the backburner. Meanwhile, nobody has caught a glimpse of the language the three senators writing the bill in the upper chamber plan to propose. That includes the Environmental Protection Agency, which must ultimately perform an analysis of the bill's economic and environmental impacts.

Nonetheless, some bits and pieces are starting to leak out. In a private phone call with supporters in late April, Sen. John Kerry (D-MA) outlined 10 components of the Senate climate bill as currently envisioned. By 2020, the U.S. would cut greenhouse gas emissions 17 percent compared to 2005 levels. That's the same goal central to the Waxman-Markey bill the House passed last summer. To reach it, the carbon pricing mechanism varies slightly. Kerry's bill exempts industrial manufacturers (at least for four years) and the oil industry from a cap-and-trade system into which electric utilities will enter. To compensate, the government will levy some form of a carbon tax on oil-based transportation.

Cap-and-trade, however, isn't the only important plank of comprehensive climate legislation. The complimentary measures supporting clean energy development and energy efficiency will play a key role in spurring the green economy and lowering energy costs for American consumers. Unfortunately, on this front, the Senate will likely rely on the substantively weak American Clean Energy Leadership Act, which passed out of the Energy & Natural Resources Committee last year. "As a standalone bill," David Roberts summarizes, "it's a minor deviation from the awful energy status quo."

So what does all this have to do with Illinois?

It all comes down to the issue of state preemption. To attract the votes of conservative Democrats and green-leaning Republicans, Kerry's bill will almost assuredly include language blocking state governments and the Environmental Protection Agency from regulating greenhouse gases. There is some obvious irony in proponents of states' rights prohibiting those same states from implementing stricter regulations than the federal government. But Sen. George Voinovich (R-OH), who is negotiating in favor of this provision, argues that "addressing climate change effectively must be done through a single, national program that replaces the existing, conflicting patchwork of rules, regulations, and lawsuits."

Environmental activists in Illinois aren't so sure. Most concede that preempting state-based carbon pricing plans with a national cap-and-trade plan makes sense. That's because greenhouse gas emissions spread beyond state borders. Currently, California has a far-reaching carbon pricing law on the books. If they push ahead with their plan while the feds implement a more lenient cap, any supplementary emission reductions secured in the Golden State will be offset by fewer reductions in other states. "For any individual jurisdiction," writes Harvard economist Robert Stavins, "the benefits of action will inevitably be less than the costs."

Local environmentalists are more concerned that state preemption will extend beyond cap-and-trade to outlaw existing state regulations that generate investment in green technology and energy efficiency. During the Bush years, states took the leading role in tackling climate change, passing legislation on this front.  Indeed, a report published late last year estimates that state actions will limit carbon dioxide emissions by approximately 537 million metric tons by 2020. "The federal government hadn't played much of a role on the issue for eight years," says Doug Scott, director of the Illinois Environmental Protection Agency. "That's where the states jumped in."

The U.S. House bill was fair on this issue, making no explicit attempt to preempt states except on cap-and-trade. If complete preemption is required to get the bill through the Senate, however, Illinois might see several laws pushed aside. That could include Illinois' stringent mercury limit, its renewable energy portfolio standard (which will save 11 million metric tons of emissions by 2020 and has already kick-started the state's wind industry), and incentives for the development of energy-efficient affordable housing and public sector building construction.

Aside from the environmental effects, full preemption would also rob Illinois of its future potential to innovate and attract green investments.

"There are so many sources of global warming pollution and so many good ideas to mitigate it that states can push," says Jack Darin, director of the Illinois Sierra Club.

"We don't want to get cut out," adds Scott.

When the Senate bill is officially released, we will know where the upper chamber stands on this issue. Now would be a good time to remind our senators how important state-based environmental efforts really are.