By Inside Climate News.

The fossil fuels that President Donald Trump so brashly promotes may seem like cheap energy sources, but they carry hidden costs that all of society is paying for—from damage caused by extreme weather and rising sea levels to the impacts of severe droughts on food and water security.

As Trump was preparing to pull the United States out of its international climate commitments, some of the world's leading economists issued a report that puts a figure to the price on carbon needed to reduce emissions to rein in climate change and compensate for those external costs. It's significantly higher than what most major economies have in place today.

The authors, led by former World Bank Chief Economists Nicholas Stern and Joseph Stiglitz, say carbon dioxide emissions will need to be priced at $40 to $80 per ton by 2020 to be high enough to change behaviors and shift investments away from high-emissions fossil fuels and toward cleaner energy. That rises to $50 to $100 per ton by 2030.

Even then, the report says, governments may need to pair a carbon price with other policies, such as efficiency standards, to lower emissions fast enough to keep global temperature rise well below 2 degrees Celsius, the goal of the Paris climate agreement.

"While the design of these packages will vary, based on national and local circumstances," the economists argue, "a well-designed carbon-pricing system is an indispensable part of a strategy for reducing emissions in an efficient way."