Maryland Gov. Larry Hogan (R). (Patrick Semansky/Associated Press)

TO COMBAT global warming, you need to reduce carbon dioxide emissions — and you have to do so at reasonable cost, because everyone relies on affordable energy. The principles are simple, but the policy is hard to get right. See, for example, the debate the leaders of Maryland are waging.

Gov. Larry Hogan (R) and the Democrat-dominated General Assembly agreed last year that the state should cut greenhouse gas emissions 40 percent below 2006 levels by 2030. But Mr. Hogan then vetoed a policy that would help achieve the goal: expanding how much of Maryland’s electricity must come from renewable sources. The existing mandate requires the state to reach 20 percent renewable by 2022; the vetoed bill would have upped that to 25 percent by 2020. The General Assembly is likely to try to override the veto in its new session, beginning Wednesday.

There were some good reasons for Mr. Hogan to be concerned. Maryland’s Department of Legislative Services estimates the mandate would add between $0.77 and $3.03 to the average monthly energy bill in 2020, the costliest year of implementation. More efficient policies, such as a carbon tax or cap-and-trade program, would reduce emissions at lower cost by eliminating government micromanagement.

But Mr. Hogan did not propose a market-based alternative; in fact, his counterproposal is worse than the legislature’s. The governor would spend on green-jobs training, electric car tax credits and a Green Energy Institute at the University of Maryland. At a cost of $65 million, his initiatives might not prevent a single ton of carbon dioxide from entering the atmosphere. Mr. Hogan, that is, would micromanage more and accomplish less. The legislature’s plan is less than ideal but possibly the best that current politics allow. The governor’s is not much of a plan at all.

Hydraulic fracturing is the other major energy issue the General Assembly will take up. Here, the tables are turned: Some lawmakers appear determined to push through a senseless ban on the technique, which is used to extract oil and natural gas from underground shale formations. Mr. Hogan counters that fracking should be allowed to proceed, with serious regulation. The governor is right. Fracking’s major risks can be regulated to a minimum, as the Obama administration, various Western-state governors and others have concluded. Natural gas, meanwhile, burns much cleaner than coal, its direct competitor. The fracking revolution has made the fuel very affordable, and substituting gas for coal has reduced carbon and other pollution.

The legislature should be working with the governor to finalize fracking rules, not indulging unfounded anti-fracking absolutism. Mr. Hogan, meanwhile, should be pushing the legislature to make Maryland’s climate change policy more efficient, instead of acting as a roadblock to significant emissions-cutting policy.