Future increase in rocket launches could damage the ozone layer, NOAA says

Just when the world seems to be on the cusp of much cheaper access to space — with more and more rocket launches expected over the next two decades, a new study reminds us that such advances often come at a price.

This new NOAA (National Oceanic & Atmospheric Administration) study, detailed in a paper just published in The Journal of Geophysical Research: Atmospheresshow that even “modest” injections of black carbon particles from rocket launches can affect Earth’s upper atmosphere.

We modeled the stratosphere’s climate response to potential black carbon emissions from rockets burning kerosene fuel, Christopher Maloney, the paper’s lead author and a research scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) and NOAA in Boulder, Colorado, told me. Our research focused mainly on a plausible annual release of 10 Gg (10,000 tons) of black carbon and its impact on the stratosphere, he says.

The authors note that a heavy launch vehicle using kerosene-fired engines emits on the order of ten tons of black carbon into our stratosphere with each launch.

Current annual emissions from space travel are about 1 Gigagram (Gg) per year (1,000 metric tons), says Maloney. An emissions scenario of 10 Gg per year could potentially be achieved by 2040 if industry forecasts come true, he says.

Prior to our research, only chlorinated solid-fuel rockets were thought to cause ozone loss, Maloney says. But we conclude that the depletion of the ozone layer from a kerosene rocket with high black carbon emissions is on a scale comparable to the ozone loss from solid-fuel rocket launches that emit chlorine gas, he says.

The fear is that a marked increase in rocket launches over the next decade will only exacerbate problems with Earth’s protective ozone layer.

And the authors note that in the next decade, even submicron aerosols generated during increased reentry events from defunct satellites will also enter Earth’s atmosphere and cause changes in our stratosphere.

How does all this affect our stratosphere and climate?

With emissions of 10 Gg per year, poleward of latitude 30 degrees north, our stratosphere and climate began to experience total ozone loss in the column year-round, Maloney says. The most serious loss occurred in the northernmost latitudes during the northern hemisphere summer, he says.

Heating caused by stratospheric black carbon can cause shifts in stratospheric dynamics, Maloney says.

Black carbon in the stratosphere can also cause changes in Earth’s upper atmospheric jet streams, Maloney notes. These zonal wind characteristics are important in controlling large-scale weather patterns in our lower atmosphere, he says.

Is there a way to reduce these missile emissions?

Of the main types of propellant in use today, only hydrogen-powered rockets don’t emit black carbon, Maloney says. Further research is needed to understand which type of propellant has the least impact on the climate and the ozone layer, he says.

What’s next?

The actual amount of black carbon produced by rocket engines in the stratosphere has never been measured directly, Maloney says. So measurements of high-altitude aircraft in different rocket plumes are another priority, he says.

Realistic future emissions scenarios will depend on measuring the actual black carbon emissions associated with the different types of propellant, Maloney says. This is especially the case for methane-fired rockets, which will be the main growth area for the launch industry, he says.

If rocket launches double in the next ten years, what does our stratosphere stand for?

The recent surge in launches is powered by kerosene-fired rockets, which have relatively high levels of black carbon emissions, Maloney says. Future launch growth will likely be powered by methane-fired rockets that are expected to have relatively smaller black carbon emissions than other propellants, he notes.

But until we know more about methane-fired rockets, we can’t predict with much confidence how black carbon emissions will change in the future, Maloney says.

What if humanity’s spaceflight goals get even more ambitious?

If space targets come to colonize Mars, we can be confident that rocket emissions will increase by much more than a factor of ten in the coming decades, Maloney says.

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