Future Rocket Launch Increases Could Harm Ozone Layer, Says NOAA

Just when the world seems to be on the cusp of much cheaper access to space —- with more and more rocket launches projected to take place in the next two decades, a new study reminds us that such progress often comes at a price.

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

We modeled the climate response of the stratosphere to potential emissions of black carbon 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 study primarily focused on a plausible 10 Gg (10,000 metric tons) annual black carbon emission and its impact on the stratosphere, he says.

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

Current annual emissions from space travel is approximately 1 Gigagram (Gg) per year (1000 metric tons), says Maloney. A 10 Gg-per-year emission scenario could possibly be reached by 2040 if industry projections come true, he says.

Prior to our study, only chlorinated solid fueled rockets were thought to cause ozone loss, says Maloney. But we conclude that ozone depletion from high black carbon-emitting kerosene rocket is on a scale comparable to the ozone loss from solid fueled rockets 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 over the coming decade, even submicron aerosols generated during increased instances of re-entry by defunct satellites will also enter Earth’s atmosphere and could cause changes to our stratosphere.

How does all this impact our stratosphere and climate?

With 10 Gg-per-year emission, poleward of 30 degrees North, our stratosphere and climate began to experience year-round total column ozone loss, says Maloney. The most severe loss occurred at the northernmost latitudes during the Northern hemisphere’s summer, he says.

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

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

Is there a way to mitigate these rocket emissions?

Of the main propellant types in use today, only hydrogen fueled rockets do not emit black carbon, says Maloney. Further research is required to understand which propellant type has the smallest impacts on 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, says Maloney. So, measurements from high altitude aircraft in various rocket plumes are another priority, he says.

Realistic future emission scenarios will depend on measuring the actual black carbon emission associated with the different propellant types, says Maloney. This is especially so for methane fueled rockets that will be the main area of growth for the launch industry, he says.

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

The recent increase in launches is driven by kerosene fueled rockets, which have relatively large black carbon emissions, says Maloney. Future launch growth will likely be driven by methane fueled rockets that are expected to have relatively smaller black carbon emission than other propellants, he notes.

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

And if humanity’s spaceflight goals become even more ambitious?

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

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