Prohibit weather modification.

The bill prohibits geoengineering activities within Montana but makes an explicit exception for traditional cloud seeding practices used for water resource management, which remain permitted.

To clarify the scope of these restrictions, the legislation sets forth the following provisions: Specifically banned practices include stratospheric aerosol injection. Also forbidden are solar radiation management techniques like space-based reflectors and cloud albedo enhancement. Marine cloud brightening, which involves spraying sea-salt particles into marine clouds to increase reflectivity and reduce the amount of solar radiation absorbed by Earth, is also prohibited.

In addition, solar radiation management is likewise prohibited.

Marine cloud brightening is explicitly banned.

The Legislature states its rationale for these prohibitions. It justifies these actions by determining that geoengineering poses risks to the environment and public health. The risks stem from its experimental nature and potential for unintended consequences.

Explicit exception: Cloud seeding is not prohibited by the bill. Specifically, cloud seeding—defined as increasing precipitation within existing cloud systems to support water resource management, such as for agriculture and snowmaking—remains legal and continues to be regulated under Title 85, Chapter 3, of the Montana Code Annotated.

The prohibition is incorporated in Title 75, Chapter 2, of Montana's environmental laws and is subject to its enforcement provisions.

Although the bill does not specify penalties or enforcement mechanisms, it incorporates the provisions of Title 75, Chapter 2. These provisions govern environmental quality and provide a framework for enforcement. By referencing existing legal structures, the bill indirectly addresses enforcement.

Effective date: The act becomes effective immediately upon passage and approval.

This bill had a dramatic and turbulent path through the legislature, surviving a near-death experience on the Senate floor before ultimately failing in the House. The bill was assigned to a drafter in November 2024 but did not enter active drafting until mid-February 2025, with introduction occurring on February 25. Senate Natural Resources held a hearing just three days later and passed the bill on March 3. However, the Senate floor proved contentious: on March 5, after an amendment was adopted, the bill was indefinitely postponed and a motion to pass failed. In an unusual procedural reversal, the Senate reconsidered its action and returned the bill to second reading. The following day, March 6, the bill passed both second and third readings and was transmitted to the House.

House consideration moved more slowly, with the bill waiting ten days before referral to the House Natural Resources Committee. After a hearing on March 24, the committee took two weeks before voting to concur with amendments on April 7. When the bill reached the House floor for second reading on April 10, members voted "Not Concurred," rejecting the measure just as the House had done with the 2021 bill. The bill formally died in process on May 23, 2025, following what appears to be a session adjournment, marking another instance of a geoengineering-related measure clearing the Senate only to fail on the House floor.