Saskatchewan Premier Brad Wall is weighing in on the federal election — a week after suggesting he might lay low for the campaign.

The issue that inspired Wall to send out a tweet on his Twitter account — and later talk to reporters — was the Liberal's environment platform released on the weekend.

In particular, Wall is questioning the Liberal plan for a "cap-and-trade" system to control greenhouse gases.

Cap-and-trade is described in the platform as "a mechanism that sets a ceiling on the total amount of permissable greenhouse gas emissions by large industrial facilities, and then auctions off emission permits to companies who can trade them amongst themselves to remain compliant under the law."

In the 2008 election, Wall openly opposed a different Liberal plan to cut greenhouse gases. The "Green Shift" plan, which was never implemented, proposed boosting carbon taxes by $15 billion while reducing income and other taxes by the same amount.

Last week, Wall said he'd take a lower profile on federal issues during the 2011 campaign.

But on Monday, he was musing whether the Liberal's new cap-and-trade plan is "Green Shift 2."

Speaking to reporters, he acknowledged that the federal Tories have also promised cap-and-trade, but said the difference is where the money will go.

"There certainly appears to be a plan [in the Conservative version of cap-and-trade] to let provinces work within their own borders," Wall said. "We've developed a plan to do that. So that we will have ... a fee for high emitters, but that money will stay in the province, in a tech fund."

Wall says cap-and-trade money that Saskatchewan keeps would then be used to develop technology to reduce greenhouse gas emissions. If the Liberals would also allow provinces to keep the money, Saskatchewan would have no problem with their plan either, he said.