Final answer:
Compelling evidence for the claim that national environment groups are more impactful includes the amplification model of organizations like the Sierra Club, historical motivators such as the Iraq War's impact on U.S. elections, and the ability of national groups to conduct influential scientific and economic studies.
Step-by-step explanation:
To support the claim that volunteering with a national environment group is better than a local one because it can have a higher effect on a large number of people, one must provide compelling evidence. For instance, an illustration of the amplification model could serve as evidence where a national organization like the Sierra Club expands its influence by addressing universal issues such as reduced energy consumption and pollution, which resonates with a broad audience and mobilizes a larger community.
Another piece of evidence might cite how national concerns have historically acted as powerful motivators in political realms, such as the impact of the Iraq War on U.S. elections, demonstrating that national issues can indeed engender significant public response and engagement.
Furthermore, national groups often have the resources to conduct extensive scientific and economic studies, offering robust data that can persuasively argue for environmental protection on economic grounds, which is instrumental in policymaking, especially in low-income countries.