City fund managers are to lobby the government for clarity on emission targets after 2012, claiming the uncertainty surrounding international policy in the future is hampering investment decisions.

The group of 15 investors, led by Insight Investment, which is part of the HBOS banking group, intends to begin discussions as part of a campaign to push climate change up the agenda.

The campaign backed by the investors, who control £850bn of assets between them, aims to encourage companies and governments to reduce global greenhouse gas emissions.

Rory Sullivan, head of investor responsibility at Insight Investment, said: "The big problem for climate change is there is so much uncertainty. It's holding companies back on investment decisions ... and it's holding investors back."

In the past, investors have been reluctant to talk directly to government about policy, but Mr Sullivan said this was no longer the case for climate change.

The work is being coordinated by the larger Institutional Investors Group on Climate Change (IIGCC), of which Mr Sullivan is a member, which argues that government must lead the response to climate change "with a framework that provides incentives and investment certainty to companies and individuals".

The investors want to include the risks associated with climate change in their analysis of companies. Mr Sullivan said: "We as institutional investors recognise that the long-term interests of millions of savers whom we represent and the organisations they work for are inextricably intertwined with long-term climate issues."

The decision by the group of investors - including Morley Fund Management, F&C Asset Management and Hermes as well as Insight - to sign up to a joint statement indicates the emphasis that they are now placing on the business risks associated with climate change.

The fund managers intended to "engage" with the companies in which they invest to ensure they are "minimising the risk and maximising the opportunities presented by climate change and climate policy".