Giving prisoners their own showers has forced up the government's carbon dioxide emissions, official statistics have shown.
En-suite showers in prisons have boosted emissions
Carbon emissions within former Home Office bodies, including the prison service, rose from 28,237 tonnes in 2005-06 to 28,925 tonnes in 2006-07.
The rise has been attributed to the increase in the prison population and the provision of in-cell showers.
Last week, the prison population in England and Wales exceeded capacity.
On Friday, there were 82,068 inmates in jails - 96 over the Prison Service's "operational capacity".
This was the first time the population ceiling had been breached.
In a Commons written reply, junior justice minister Maria Eagle said the rise in CO2 resulted from an increase in the prison population and in "regime facilities", such as the provision of in-cell showers as opposed to communal showers.
The figures relate to the Home Office before it was split into two separate departments for security and for justice in April last year.
Last year, Prime Minister Gordon Brown committed the UK to reducing carbon dioxide emissions by 60% before 2050 to help tackle global warming.