The correct answer is (a). The United Nations Framework Convention on Climate Change (UNFCCC) was adopted on May 9, 1992, at the United Nations Conference on Environment and Development (UNCED), also known as the Earth Summit, in Rio de Janeiro, Brazil. It entered into force on March 21, 1994. The UNFCCC is an international environmental treaty with the goal of stabilizing greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. As of November 2021, 197 parties have ratified the UNFCCC.
The UNFCCC is the first international treaty to address climate change. It sets out a framework for action by countries to mitigate climate change and adapt to its effects. The UNFCCC also establishes the principle of common but differentiated responsibilities, which recognizes that developed countries have a greater responsibility to address climate change because they have historically contributed more to the problem.
The UNFCCC has been successful in raising awareness of climate change and in mobilizing international action to address it. However, it has not been able to achieve its goal of stabilizing greenhouse gas concentrations in the atmosphere. This is due to a number of factors, including the lack of binding commitments from countries to reduce their emissions, the difficulty of reaching agreement on how to share the costs of climate change, and the continued growth in greenhouse gas emissions.
Despite its shortcomings, the UNFCCC remains an important tool for addressing climate change. It has provided a framework for international cooperation on climate change and has helped to raise awareness of the issue. The UNFCCC is also a valuable source of information and guidance for countries that are developing their own climate change policies.
The other options are incorrect because they are not the dates on which the UNFCCC entered into force.