The European Supervisory Authorities (ESAs), along with the European Central Bank (ECB), conducted a "Fit-For-55" climate scenario analysis to assess the impact of the EU's green transition on its financial system. The analysis used three scenarios, including a baseline and two adverse scenarios involving "Run-on-Brown" shocks, where investors divest from carbon-intensive firms. Transition risks alone are deemed unlikely to threaten financial stability, but combined with macroeconomic shocks, they significantly increase losses for financial institutions. The study utilized top-down models to assess both direct and indirect impacts across banking, insurance, pension, and investment fund sectors. Results show limited losses under the "Run-on-Brown" scenario alone, but substantially higher losses when combined with adverse macroeconomic conditions. First-round losses ranged from 5.2% to 6.7% under the first adverse scenario, rising to 10.9% to 21.5% in the second. Second-round losses are most impactful for investment funds. The findings highlight the need for coordinated policy and comprehensive climate risk management by financial institutions. The analysis, while innovative, acknowledges significant uncertainties due to methodological and data limitations. The collaborative effort aims to inform policy decisions to support the green transition while mitigating financial system risks.