Image copyright Getty Images Image caption Huge efforts will need to be made to protect forests

Forests around the world will need to be expanded by 5-15% to limit global temperature rises to 2C.

And crop yields must rise by 40-60%.

These are just two predictions for 2050 of an online tool developed by the government to consider options for cutting carbon emissions.

The Global Calculator uses data reviewed by international experts to look at scenarios for meeting the 2C target, which scientists say is needed to avoid dangerous climate change.

Led by the Department of Energy and Climate Change (Decc), the model of the world's energy, land and food systems suggests living standards can be maintained, but only by making sweeping changes to agriculture, transport, food and fuel.

There would need be hundreds of million electric cars on the road by 2050, and the amount of CO2 emitted per unit of electricity would need to fall by at least 90%.

Ambitious targets

Consumers would also need to think about switching to diets high in vegetables or eat meat from animals raised through intensive farming.

Energy and Climate Change Secretary Ed Davey said: "For the first time this Global Calculator shows that everyone in the world can prosper while limiting global temperature rises to 2C, preventing the most serious impacts of climate change.

"Yet the calculator is also very clear that we must act now to change how we use and generate energy and how we use our land if we are going to achieve this green growth."

Dr Mike Cherrett of Climate-KIC, the EU climate initiative that co-led the project, added: "The calculator clearly highlights that we can meet our 2C target while maintaining good lifestyles - but we need to set ambitious targets on all fronts and use innovation to address climate change."

The global calculator builds on Decc's UK calculator, published in 2010. It is being offered to other governments for use in the run-up to crucial climate negotiations in Paris at the end of the year.