三、(26 分)國際能源署(International Energy Agency, IEA)自 1998 年起每年出版《世界能源展望》(World Energy Outlook, WEO)，最新發布《2017 世界能源展望》(WEO-2017)，列出四種情境(scenario)，請先中譯以下內容(https://www.iea.org/publications/scenariosandprojections/) (http://www.iea.org/media/weowebsite/2017/Chap1_WEO2017.pdf)：

New Policies Scenario of the World Energy Outlook broadly serves as the IEA baseline scenario. It takes account of broad policy commitments and plans that have been announced by countries, including national pledges to reduce greenhouse-gas emissions and plans to phase out fossil-energy subsidies, even if the measures to implement these commitments have yet to be identified or announced.

Current Policies Scenario assumes no changes in policies from the mid-point of the year of publication (previously called the Reference Scenario).

450 Scenario sets out an energy pathway consistent with the goal of limiting the global increase in temperature to 2°C by limiting concentration of greenhouse gases in the atmosphere to around 450 parts per million of CO₂.

Sustainable Development Scenario is introduced for the first time in the WEO-2017 and takes a fundamentally different approach from those discussed above. While the Current Policies and New Policies scenarios start with certain assumptions about policies and see where they lead the energy sector, the Sustainable Development Scenario (as with the previous 450 Scenario) starts with a certain vision of where the energy sector needs to go and then works back to the present.

再請回答以下問題：(1)請定義何謂「永續發展 sustainable development」；(2)請說明「溫室氣體濃度 greenhouse-gas concentration」與「氣候變遷 climate change」之關係。