* Any views expressed in this opinion piece are those of the author and not of Thomson Reuters Foundation.

No geoengineering solution can replace emissions reductions - and to suggest otherwise would be "profoundly counter-productive"

I am on my way to Bonn to participate in the 23rd meeting of the Conference of the Parties (COP23) of the U.N. Framework Convention on Climate Change. Over the next fortnight, governments from across the world will gather here to shore up their commitments to reduce greenhouse gas emissions.

In the same week, however, on November 8, a number of eyes will be on another less well-advertised, but potentially significant, climate-related event in Washington.

The U.S. House’s Subcommittees on Environment and Energy will hold a hearing on geoengineering, and specifically look into research on a branch of technologies known as solar geoengineering, or solar radiation management.

It is not yet clear what will come of the Washington hearings, nor is it clear to what extent they will acknowledge the human causes of climate change. I am concerned, however, that some may latch on to the idea of solar geoengineering as an alternative to greenhouse gases reduction. That would be wrong, and dangerous.

The overwhelming priority to tackle rising temperatures is to cut, and eventually eliminate, greenhouse gas emissions – and to do so far more quickly than currently envisaged.

Even if all the Paris commitments are met – and that’s a big if – the world will still be on track to warm to more than 3 degrees Celsius above the pre-industrial average. As we are already seeing, even today’s 1 degree Celsius warming leads to catastrophic weather events. The prospect of a 3 degree or higher world is intolerable.

To that extent, the deliberations at COP23 remain paramount. Governments must not only meet their current commitments, but improve upon them. I wish them all the best in this challenging endeavor.

At the same time, there is a growing recognition that mitigation will almost certainly not be enough. Earlier this week I attended the launch of UN Environment’s 2017 Emissions Gap Report. It makes for sobering reading: warning that keeping temperature rise to within international targets of 1.5-2 degrees Celsius will likely rely extensively on another branch of geoengineering technologies, known as carbon removal, or negative emissions technologies.

“There are no scenarios available that can keep warming below 1.5 degrees Celsius by 2100 without removing carbon from the atmosphere via negative emissions technologies,” it says. “Delay in adequate near-term climate action swiftly locks 2 degree Celsius pathways deeply into negative emissions.”

Yet at present, no negative emissions technologies exist at anything near the scale or cost to make the necessary reductions, and there has been almost no serious governmental debate about the profound societal challenges involved in implementing them.

“Scenarios that show net emissions turning negative in the second half of the 21st Century can give the false impression that there is no urgency,” the report says. “However, to achieve those scenarios will require significant amounts of gross negative emissions by 2030 at the latest, and advancing techniques to maturity usually takes decades.”

That is why some scientists are arguing that a form of solar geoengineering might be needed to manage a period of temperature overshoot, until emissions are brought to net zero, and carbon removal techniques become more widespread.

It is crucial to understand, however, that none of these scientists are proposing that solar geoengineering can replace emissions reductions, or potentially carbon removal. On the contrary, to deploy a stratospheric sunscreen without tackling the underlying causes of climate change could introduce a major termination risk, with humankind locked into deploying it for centuries.

Neither would solar geoengineering address issues such as ocean acidification, and it would introduce new challenges – such as how to deal with potentially unequal effects on precipitation at high levels of deployment, and how these effects should be monitored.

This all leads to a delicate, yet necessary balance in public policy.

We must remain primarily committed to rapid emissions reductions, whilst at the same time being open to the possibility that other techniques may be needed if we are to keep temperature rise to within 1.5 to 2 degrees Celsius.

Well-governed research on geoengineering – which balances both regulation and enabling elements – could provide answers to many questions concerning the risks and potential benefits of geoengineering technologies.

To that extent, we commend the University of Calgary’s recent publication of a Code of Conduct for Responsible Geoengineering Research, and would urge institutions involved in research, or funding research to consider applying it to their work.

We also encourage a significant broadening of the conversation. Geoengineering is a matter for all society, worldwide, as it affects us all. This means we need to hear many more voices than currently being heard in the geoengineering debate, including events like the November 8 hearing.

But for any country to focus on geoengineering research instead of focusing on mitigation would send a profoundly counter-productive signal, and strengthen the position of those who think that research is the “slippery slope” to premature deployment.

This signal would be particularly strong coming from the United States, since the U.S. government has announced its intention to withdraw from the Paris Agreement. Taken in this context, the danger is that this hearing poisons the well of future international debate on geoengineering technologies.

Similarly, any federal appropriations at this moment for solar geoengineering research would sow seeds of distrust around the world, especially if announced while COP23 debates the urgent need for radical decarbonization.

To that end, I see some grounds for hope in the commitment to mitigation shown by some U.S. states, such as for example the states of California or Washington, as well as initiatives by a number of private corporations. These are examples to highlight, and to emulate.

So a simple plea: I urge all participants in the Congressional hearing next week to assert the reduction of CO2 emissions as the primary mechanism to tackle climate change. And then, and only then, to set about a serious and thoughtful discussion about the possibilities offered by geoengineering technologies, and the enormous research and governance challenges that they bring to bear.