In the decade since global central banks bought trillions to send credit to those they thought deserving, growth fluttered barely above flat line while economic inequality has grown steadily worse, especially in the U.S. Undeterred, global central banks yesterday announced a new venture: a green-bond fund adding their awesome resources to the fight against climate change. The IMF joined in, calling climate change an “existential challenge” warranting structural change in global financial policy. But, there are other really existential threats – for example, those to lives cut short because biomedical research takes too long and leaves too many behind. I don’t discount at all the threat of global warming, but I fear that any time financial policy picks a fiscal favorite, other critical challenges are starved of public and private capital even as central bankers and supervisors venture into new fields in which they have negligible expertise.

We know that unduly large amounts of public debt crowd out private investment and innovation. We have now also learned the hard way that large amounts of assets on central-bank balance sheets crowd out capital formation in favor of financial-market speculation. There is thus much to fear if global central banks engage in the social-impact finance marketplace even as global financial supervisors order their charges to do more for a single public-welfare priority.

I’ve no quarrel with the grave fears about a shuddering planet that underpin these heartfelt calls. What troubles me is what happens to other social-welfare challenges – for example, ending the suffering and early death caused by untreated disease or continuing, unnecessary disability. Long-delayed medical cures are no more a fact of life than a warming planet – money will make a material difference and the public good would benefit enormously thereby. I’m not saying that central banks should add bio bonds to their green bond holdings; I am saying that the more green bonds central banks buy, the less there is to go around in the global financial market for anything else.

I’ve learned a lot about biomedical finance in our efforts to come up with a new federal guarantee that uses the tried-and-true engine of fiscal policy to support private investment. One thing I know all too well is that the early stage, “translational” research essential to successful new treatments is starved for investment. Once public and foundation investment leads to hope-inspiring theories, it takes a lot of private-sector money ($2.6 billion per drug) to move these ideas through costly, early-stage trials before venture capital and large biopharma companies take research across the finish line. It’s for this reason that the space between basic science and late-stage research is known as the “valley of death.”

Many of us know this valley too well, reading scientific reports about possible new drugs and devices that then take years – years some do not have – to turn into the miracle treatments so many seek. For someone sitting in a cancer ward looking out at the sunshine, it matters little that it’s too hot outside. What of course matters is seeing the next sunrise. A blind child picking her way with a white cane through puddles in a flooded city faces a set of life challenges far worse than getting wet.

With effective fiscal policy, we wouldn’t have to choose between climate change and biomedical treatment, but of course we don’t have effective fiscal policy in the U.S. or many other nations. It’s understandable that, despairing of forward-looking decisions on the fiscal side, financial policy-makers want to step in when they see the seas rise around them as it gets hotter and hotter and drier and drier. Even so, this is a choice of one public good over many other compelling ones. The financial-policy toolkit has many other implements readily at hand with which financial policy can make a meaningful difference without venturing into high-risk investment in a single sector at so much risk to so many others.