According to the PMBOK Guide, an issue is "a point or matter in question or in dispute, or a point or matter that is not settled and is under discussion or over which there are opposing views or disagreements" (p. 720).
Issues can arise from any aspect of the project, such as changes, risks, quality, stakeholders, etc. The issue log is a project document that records and tracks the issues that affect the project, along with their status, resolution, and ownership. The issue log is updated throughout the project as new issues are identified, analyzed, and resolved.
In this question, the change in environmental regulations is an external factor that could affect the project scope, schedule, cost, quality, or other aspects. Therefore, it is an issue that needs to be documented and tracked in the issue log. The project manager should update the issue log as an immediate action to ensure that the issue is properly addressed and communicated to the relevant stakeholders. Updating the issue log will also help the project manager to monitor and control the project performance and take corrective or preventive actions as needed.
Updating the project baseline, the risk management plan, or the change request log are not immediate actions that the project manager should take in this situation. The project baseline is the approved version of the project scope, schedule, and cost that serves as a reference for measuring and reporting the project performance. The project baseline can only be changed through the formal change control process, which requires a change request. The risk management plan is a subsidiary plan of the project management plan that describes how risk management activities will be planned, implemented, and monitored throughout the project. The risk management plan can also be changed through the change control process, if necessary. The change request log is a project document that records and tracks the change requests that are submitted, reviewed, approved, or rejected during the project. A change request is a formal proposal to modify any document, deliverable, or baseline of the project.
The project manager may need to update the project baseline, the risk management plan, or the change request log later, after analyzing the impact of the issue and determining the appropriate response. However, these are not immediate actions that the project manager should take before updating the issue log. References:
* PMBOK Guide, 6th edition, Project Management Institute, 2017, pp. 123, 129, 152, 456, 720.
* PMP Sample Test Questions, Project Management Institute, 2019, p. 15.

The question describes sensitivity analysis, which is a tool and technique of the Quantitative Risk Analysis process. Tornado diagrams are often used to display sensitivity analysis data.

Section: Planning