The world’s biggest economies have recently reduced financial support to consumers and producers of fossil fuels, but a recent study says those steps may have a limited impact on cutting greenhouse gas emissions.

Two Paris-based organizations have been keeping tabs on countries’ steps toward reducing support for greenhouse-gas-emitting fossil fuels since the world’s biggest economies in 2009 committed to gradually eliminating subsidies.

And global subsidies have fallen among the world’s major economies, although they still top $150 billion annually, the...