Impax Environmental Markets, the UK's largest environmental investment trust, was launched in 2002, and now has £1.2bn of total assets, according to AIC data. The broad investment proposition hasn't changed since launch, says Forster: "The thesis is that companies that are finding solutions to environmental challenges are going to grow at a faster rate compared with the global economy. And if we can understand that sector well and pick the right stocks, we can translate that growth into long-term outperformance of global equities."