Labour and the Liberal Democrats today published their green manifestos, highlighting wide differences between the two parties on how the UK will be powered in the future.

Labour announced support for new low-carbon "economic areas" in each region, and 5,000 new apprentices in the clean-tech economy. The Lib Dems gave more details about their ambitious main manifesto pledge to create a zero-carbon Britain by the middle of the century.

In addition to their earlier promise to generate all electricity from renewable sources – and at least three-quarters from offshore wind and marine or tidal power – the Lib Dems said Britain would have to slash emissions from transport, heating buildings, industry and agriculture. The UK could offset up to 10% of emissions by buying credits from overseas projects.

Labour sources said the pledge was an "empty gesture" as MPs had already voted for an 80% cut in emissions by 2050. Last week, the party attacked the Lib Dems for saying such targets could be met without using nuclear power, which Labour and the Conservatives support.

Simon Hughes, the Lib Dem shadow climate and energy spokesman, told the Observer that the greater use of renewable energy in Scandanavia, the Netherlands and Germany showed that much more could be done, and privately other European politicians have spoken of decarbonising their economies without nuclear power.

The Lib Dems want to focus on insulation programmes for homes and public buildings, and on boosting renewable energy industries, including a major apprenticeship scheme. The party said these plans would receive £3.1bn from other spending programmes in the first year, and income from a tax on planes in future years.

Labour sources said low-carbon zones could provide a focus for different industries to work together. Existing examples include a marine energy hub in the south-west and an emerging electric car industry in the north-east. Other possible coalitions include carbon capture and storage for coal power in Yorkshire and Humberside.

Nick Clegg, the Lib Dem leader, said in his party's green manifesto that the Tories "talk the talk on green issues only to align themselves with climate deniers in the European parliament", and claims that voting for the Green party is a waste because they "cannot make a difference in Westminster".