Reuters: Big emerging economies will come under pressure on Wednesday to respond in kind to an initiative by rich countries to work towards a target of at least halving their global greenhouse gas emissions by 2050. The Group of Eight (G8) industrial nations want the leaders of eight fast-growing countries to adopt a “shared vision” of tackling global warming in U.N. negotiations due to conclude in Copenhagen in December 2009. “There has been major progress on the climate …