The National Assembly for Wales has slashed its energy emissions by a third since 2009.
The latest figures, published in the Assembly's Carbon Management Plan, reveal that the Assembly has achieved a 35 per cent reduction in energy emissions since the base year 2008/09.
During the same period the Assembly has also achieved a 29 per cent reduction in net greenhouse gas emissions.
The Carbon Trust has identified this as an excellent standard of performance within the Welsh public sector.
However, the Assembly Commission has committed itself to reaching tough new targets with its energy "route map" setting a challenging further 30 per cent reduction by 2021.
"I think the Assembly has an impressive record in reducing its own energy emissions," said the Presiding Officer, Dame Rosemary Butler AM.
"The Assembly's success has come from working in partnership with the Carbon Trust and other specialists, and I would also like to take this opportunity to thank the staff working in the Assembly's Sustainability and Facilities Management teams and the efforts made by all occupants in achieving these impressive results.
"But we will not rest on our laurels – the Assembly Commission is committed to reducing emissions further and this has been demonstrated through these tough new targets."
The Energy Reduction Route Map was approved by the Assembly Commission in June last year.
It commits the Commission to the continued improvement of the estate's environmental performance and the setting of new targets for waste, water and business travel.
Peter Black AM, the Assembly Commissioner with responsibility for the estate and sustainability, said: "As we look towards 2021, we have an opportunity to build on our success to date, work even harder to optimise the efficiency of our buildings and embed a truly sustainable work culture.
"However, this will not be easy and will require even greater acceptance of change by the stakeholder groups using our estate.
"Yet, we will not lose sight of the key priority of ensuring we maintain a comfortable working environment for all occupants that supports the business of the Assembly and its Members."