We need to draw down carbon—not just stop emitting it

The UN's climate panel warns that the world may need to remove billions of tons of carbon dioxide from the atmosphere each year in the coming decades, on top of rapid emissions cuts, to prevent or pull the planet back from increasingly dangerous warming levels.

A growing number of research groups and startups are working on a variety of ways to do this, including building greenhouse-gas-sucking factories and using various minerals to lock up carbon on land or in the oceans.

But carbon removal has become a touchy topic. There are real concerns that the growing focus on drawing down the greenhouse gas could encourage governments and businesses to delay or even avoid the most obvious and direct way of addressing climate change: preventing emissions from reaching the atmosphere in the first place.

The convenient perception that we might be able to continue pumping out large levels of carbon dioxide and simply clean up the atmosphere in the future is an example of what's known as a moral hazard." It risks perpetuating the use of fossil fuels and pushing off the costs of dealing with climate change onto future generations.

This is a legitimate concern. Some companies have erroneously suggested that carbon removal could allow us to keep emitting at nearly half current global levels. But that would necessitate sucking up and storing away carbon dioxide at levels that are almost certainly technically, environmentally, or economically infeasible, or possibly all of the above.

There is, however, also a real risk that stigmatizing carbon removal over moral hazard concerns creates an even greater danger: deferring much-needed investment and imperiling our ability to reach future climate goals. Unfortunately, after decades of delay, there are now simply few paths to meeting our climate goals that don't require both slashing emissions today and building the capacity to suck up vast amounts of carbon dioxide in decades to come.

Emissions cuts aren't enough

Why is carbon removal needed in the first place, and why can't we just stop climate change by getting to absolute zero" emissions? The recent UN report identifies four different roles for carbon removal in climate modeling scenarios that limit warming to well below 2 C over preindustrial levels by 2100.

First, while fossil fuels can be replaced with clean energy alternatives across much of the economy, there will be some ongoing carbon dioxide emissions from sectors that are hard to fully decarbonize. These are major industries, like aviation, cement, and steel production, where we simply don't have affordable, scalable carbon-free technologies available. While more work needs to be done to understand just how low our carbon dioxide emissions can get, these sorts of sectors will likely continue to produce a few billion tons per year that need to be neutralized through carbon removal.

Second, carbon dioxide isn't the only greenhouse gas that is warming the planet. Others, including methane and nitrous oxide from sources like cattle, animal waste, and fertilizer use, are much more difficult to fully eliminate.

The recent UN report found that available technologies could probably reduce emissions of these gasses by around 50%, with additional behavior changes such as dietary shifts pushing that to 66%. However, carbon removal would have to counterbalance the sizable amount remaining.

Third, it is increasingly likely that the world will overshoot our most ambitious climate target-limiting warming to 1.5 C. We are living in a world that has already warmed by 1.2 C, leaving a vanishingly small carbon margin to work with.

Unfortunately, even if we get carbon dioxide emissions all the way down to zero, the world will not cool back down; it will just stop warming up. The only way to permanently reverse warming is through carbon removal.

Finally, carbon removal can be an important hedge against uncertainties in the climate system. While most of our emissions reduction scenarios aim for a 50% chance of limiting warming to 1.5 C or a 66% chance of limiting it to 2 C, it is still not clear just how sensitive the climate is to rising levels of greenhouse gas.

That means that there is a real chance we will not know how much warming will occur until it is too late to avoid it. Having viable carbon removal options can provide a way for us to respond to such unpleasant climate surprises.

While the UN report didn't spell it out, others have noted that carbon removal could also aid global climate equity, providing a means for rich countries to repair some of the damage caused by their past emissions while buying poorer nations a little more time to switch to cleaner technologies.

Managing expectations

At the same time, it is important that we recognize the need to avoid banking too heavily on cleaning up pollution after the fact. We may not be able to reduce the costs of reliable, permanent carbon removal as much as we hope, and future governments may prove unwilling to deploy it on the scales that models assume.

Even if we succeed in reducing the cost of permanent carbon removal to $100 a ton, which would be a major technical achievement, it would cost around $22 trillion to reverse warming by one-tenth of one degree Celsius.

In other words, cutting emissions today will very often be cheaper than drawing down those emissions in the future. And the cost of emissions reductions will fall as we develop more technologies to deal with the sectors of the economy that are currently too expensive to effectively clean up.

So how can we move forward to develop and scale carbon removal solutions without creating a risk of delaying the needed cuts in climate pollution?

We should start by being skeptical about any portrayal of carbon removal as a silver bullet that avoids the need for deep emissions cuts. We should ensure that any net-zero commitments from governments and corporations assign a substantially greater role for emissions reduction than carbon removal. We should be wary of any modeling that bases high use of future carbon removal on the idea that spending money to tackle climate change in the future is easier than spending money today. And as a simple rule of thumb, we should aim for a world where we reach net zero by cutting more than 90% of current emissions and removing less than 10%.

We should also avoid dubious carbon offsets and credits that don't reliably and permanently draw down greenhouse gas, and which can distort people's perceptions about the true costs of carbon removal and the hard trade-offs between drawing down emissions and preventing them in the first place.

Companies must make it a priority to reduce their climate pollution every way that they can, up and down the supply chain. They need to do rigorous and honest assessments to determine the sources and levels of whatever climate pollution they can't fully eliminate yet. And they need to build a portfolio of reliable, durable carbon removal options that will allow them to credibly achieve their net-zero goals.

Zeke Hausfather is the climate research lead at Stripe Climate and a contributing author to the IPCC Sixth Assessment Report. Jane Flegal is the market development and policy lead at Stripe Climate.