I believe it can be implemented gradually. For a start, few banks may start first (e.g: govt owned bank). Or giving incentives for banks moving into this direction.

I think neglecting our ecosystem threatens the lives of millions of people in conjunction with the global climate change scenario ... Banks, as financiers, can play a major role in this regard being the focus of economic activities

2 angles have been commonly approached.

1 - Financial stability as a result of the impact that issues especially like climate change could have on financial assets that would be correlated across the banking system. The Bank of England and ECB have both written or spoken recently about this.

BoE: https://www.bankofengland.co.uk/working-paper/2018/climate-change-and-the-macro-economy-a-critical-review

ECB: https://www.ecb.europa.eu/press/key/date/2018/html/ecb.sp181108.en.html

2 - nonsystemic risks which are not correlated across financial institutions but more idiosyncratic. Better risk taking by banks can be encouraged by different capital weights on green assets: https://www.globalcapital.com/article/b1c3gwmjk20r6w/eu-banks-must-disclose-on-esg-may-get-greenbrown-risk-capital-weights

I would like to refer to the European Bank for Reconstruction and Development (The EBRD) in supporting green development activities wirhin its approach to sustained development which consider environment and scial aspects in all financed projects during all stages, whether directly by the EDB on through banks. This constitute an example for Central Banks and Banks towards this vital missin in light of the following expressive quotation from theThe EBRD report:

" Our approach to sustainability We implement our environmental and sustainable development mandate by: • incorporating environmental and social requirements into the appraisal and implementation of all Bank-funded projects based on EU standards and international best practice • providing finance and technical assistance specifically aimed at environmental issues such as sustainable energy, climate change, environmental infrastructure and nuclear safety • promoting social inclusion through investment and other forms of support for micro enterprises and by increasing access to community services such as water and public transport • supporting projects that promote gender equality".

(https://www.ebrd.com/news/publications/special-reports/20-years-of-investing-in-the-green-economy.html)