Whether you love them or hate them, Donald Trump and Bernie Sanders have shown Americans the downsides of trade deals like Trans-Pacific Partnership and its trans-Atlantic counterpart. These deals, like NAFTA before them, aim to take down barriers to trade globally and encourage economic growth. But they also take down factories and jobs in many parts of the U.S. The economic pain they cause has become a big election year issue.

Proponents of these treaties say that economies grow stronger when companies everywhere compete on a global market. They say that this will cause inefficient and unproductive companies to shut down. Then capital and labor can flow around the world and settle wherever money and people can be most productive. So goes the theory.

But ironically, while these treaties demolish some trade barriers, the actually erect and strengthen others. Now it's emerging that one of the main effects of the treaties is to lock in huge subsidies for coal and oil – two fuels that cause most of the world's climate change. Worldwide, these subsidies totaled nearly half a trillion dollars in 2014.

Countries use a lot of excuses for subsidizing coal and oil. Some say it is for self-defense, in case their supplies are shut off. Some say it is to make sure poor people don't suffer for lack of affordable fuel. All too often the subsidies result from cronyism and corruption – and a desire on the part of undemocratic leaders to placate the restless poor in their midst.

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Whatever the reason, these subsidies are bad economics and worse for the climate. The economic damage is two-fold. First, coal and oil extraction create few jobs. The entire U.S. coal industry employs barely 65,000 people at this point, after years of decline. Renewable power sources generate more employment for the amount of power generated. Second, once nations start on the transition to renewables they put themselves on a path to spending much less on energy. The economics just get better over time: Solar cells and batteries get cheaper and more efficient every year. Wind and sunshine are free. Meanwhile fossil fuels – coal, oil, and natural gas -- cost money, even though their cost has slumped in recent years.

Beyond these economic problems, these coal and oil subsidies hurt the climate. The more coal and oil are subsidized, the more people will burn them. Less investment will flow to wind and solar. Last fall, at COP21 (a major climate conference in Paris), world leaders committed themselves to slashing carbon emissions over the next few decades. These reductions are almost impossible to achieve unless nations phase out fossil fuel subsidies.

Major global insurance companies are the world's best appraisers of risk, and they too urge heads of state to cut the subsidies. They speak up not because they are treehuggers; they speak up because they insure against flooding and other climate-related risks. They know climate change is real, and it will have real economic costs.

This week, a group of major insurance companies with more than $1 trillion in assets issued a statement directed at the leaders of the G20 nations. The insurers called for a "clear timeline" to phase out all fossil fuel subsidies in G20 nations by 2020.