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One-third of energy-related global carbon emissions come from buildings, and much of this could be avoided. One way is to impose strict energy efficiency requirements on new buildings. However, rules about new buildings make relatively little difference in the developed world. Our building-related emissions are primarily determined by the structures that already exist: the ones in which we live and work, shop and learn.

To maximise the energy-saving potential of the construction sector, the main emphasis needs to be on retrofitting existing buildings. Recent advances in technology, IT and construction enable us easily to slash energy needs for heating and cooling in most existing European buildings by up to 90%. More and more governments are realising the importance of existing building stock in emissions - and are acting.

However, most programmes cherry-pick ways to cut energy, resulting in no more than 15-40% savings in heating and cooling energy use. This is a major problem. When only some building components are upgraded, it results in a suboptimal solution - and it will be impossible or extremely expensive to come back for these missed opportunities.

This is underlined by the results of our work at the Centre for Climate Change and Sustainable Energy Policy (3CSEP), with the Global Energy Assessment and the United Nations Environment Programme’s Sustainable ºÚ¶´ÉçÇøs and Climate Initiative, to model the energy use in buildings worldwide until 2050. We find that, on a global scale, it is possible to almost halve emissions from heating and cooling in buildings by 2050, compared to 2005, despite a growing world population and higher standards of living - but only if the state of the art is applied in all retrofits. If present trends continue and we persist with our so-called ambitious policies for retrofits, then we’re not going to get anywhere close to our 2050 ambition for cutting emissions. This is a significant missed opportunity, since there are few other areas of the economy where it is financially feasible to slash emissions by such a large percentage.

Changing the boiler, adding a few centimetres of insulation to part of the building envelope, replacing a couple of windows will not provide the best whole-building solution.

Even when the efficiency of individual building components is optimised, the result is still less environmentally beneficial than when a systemic, whole-building retrofit is planned.

Upgrading a boiler or installing a heat pump sound environmentally friendly; but a well-planned and holistically constructed (retrofitted) building in most European climates actually does not need a heating system, except for small backup units, such as a fireplace or a small portable radiator. Also, the costs of a piecemeal approach are significantly higher than doing it in one go.

What does this mean for present policy-making and renovation practices?
Do it well or don’t touch it. Policies and subsidy schemes should either support holistic, deep retrofits - or wait until this becomes possible - otherwise we seriously jeopardise medium- to long-term climate targets, or at least make them very expensive to achieve. Many governments in Europe and elsewhere in the world need to re-examine or reconsider their present policies supporting building refurbishment initiatives.

Unfortunately, small is not always beautiful.

Diana Ãœrge-Vorsatz is director of 3CSEP, Central European University, Budapest

• To mark World Green ºÚ¶´ÉçÇø Week 2010, the UK Green ºÚ¶´ÉçÇø Council will launch a report - Tackling Global Climate Change, Meeting Local Priorities - on Monday 20 September at London’s City Hall. Speakers will include Boris Johnson, the mayor of London, and Diana Ãœrge-Vorsatz. To book a place, please email alexa.driver@ukgbc.org