Biodiversity is being lost at a rate not seen since the last mass extinction. But the United Nations decade-old plan to slow down and eventually stop the decline of species and ecosystems by 2020 has failed. Most of the plan’s 20 targets - known as the Aichi Biodiversity Targets - have not been met. The Aichi targets are part of an international agreement called the UN Convention on Biological Diversity, and member states are now finalizing replacements for them. Currently referred to as the post-2020 Global Biodiversity Framework (GBF), its draft was published in July 2021. It aims to slow down the rate of biodiversity loss by 2030. And by 2050, biodiversity will be “valued, conserved, restored and wisely used, maintaining ecosystem services, sustaining a healthy planet and delivering benefits essential for all people”. The GBF is a comprehensive plan. But success will require systemic change across public policy. That is both a strength and a weakness. If systemic change can be implemented, it will lead to real change. But if it cannot, there’s no plan B. This has led some researchers to argue that one target or number should be prioritized and defined in a way that is clear to the public and to policy makers. It would be biodiversity’s equivalent of the 2°C climate target.

Which of the following is the central theme of the above passage?

The correct answer is: the future of biodiversity conservation efforts at global level.

Step-by-Step Explanation:

1. Analyze the Structure and Scope of the Passage:
- The passage opens by noting the failure of past goals (the 2020 Aichi Biodiversity Targets under the UN Convention on Biological Diversity).
- It then shifts focus to current and upcoming initiatives, specifically discussing the new post-2020 Global Biodiversity Framework (GBF), its goals for 2030, and its vision for 2050.
- Finally, it discusses the implementation challenges of this new plan and suggestions by researchers for setting future target priorities (like a single top-level goal similar to the 2°C climate target).

2. Evaluate the Options:
- "the future of biodiversity conservation efforts at global level": Correct. The primary focus of the passage is outlining where global biodiversity efforts are heading post-2020, focusing on the new GBF targets for 2030 and 2050 and proposals to improve future success.
- "the reason for failure of biodiversity conservation efforts at global level": Incorrect. The failure of the Aichi targets is mentioned briefly at the start to establish context, but analyzing the detailed causes of that past failure is not the main topic of the passage.
- "the inter-relationship between biodiversity conservation and climate change": Incorrect. Climate change is only mentioned metaphorically at the very end ("biodiversity's equivalent of the 2°C climate target") to suggest setting a single clear goal.
- "the role of united Nations in biodiversity conservation at global level": Incorrect. Although UN plans (Aichi, GBF) are referenced, the passage focuses specifically on the trajectory and future frameworks of global biodiversity conservation rather than evaluating the broader institutional role of the UN.

Therefore, the central theme of the passage is the future of biodiversity conservation efforts at global level.