Ozone Loss and Climate Change Caused by Black Carbon Emissions from an Increasing Frequency of Rocket Launches

Abstract:

The number and sizes of hydrocarbon fueled rocket launches are expected to increase in coming decades. Rocket black carbon (BC) emissions into the stratosphere are therefore also likely to increase, potentially to 10 Gg yr^-1 by 2040. It is of interest to understand how this level of stratospheric BC injection, larger than aviation yet smaller than geoengineering, affects global climate and stratospheric ozone levels. The NCAR Whole Atmosphere Community Climate Model (WACCM) is used to simulate the atmosphere’s response to a 10 Gg yr^-1 rocket BC emission into the mid-latitude northern hemisphere (NH) where most of the planet’s launch sites are located. The rocket BC accumulates in the stratosphere to a steady state burden of 40 Gg in a layer between 250 and 10 hPa. This BC layer extends into both hemispheres, but is most dense in the NH. The rocket BC intercepts solar radiation (mean optical depth 0.002) and warms the NH stratosphere by as much as 1.5º C near 50 hPa between 30º N and 70º N latitude. The warming increases (decreases) the equator-to-pole temperature gradient during summer (winter), enhancing seasonal variations in radiation and associated stratospheric dynamics. The NH stratospheric westerly zonal winds near 1 hPa decrease by about 5% during winter while the easterly zonal winds during summer decrease similarly. The annual average of the zonal wind maximum decreases by about 10%. The BC warming and the resulting changes in the global circulation produce a year-round 2.75% average ozone column loss pole-ward of 60º. In the SH, the changes in circulation increase the depth of the springtime South Polar ozone hole loss by about 10%. Tropical ozone remains unchanged because of the feedback from deeper solar UV penetration. Total annually averaged global ozone loss equals ~ 18%. The NH troposphere beneath the BC accumulation cools, though only slightly. WACCM cases with rocket BC emission of 30 and 100 Gg yr^-1 show the relative importance of the different feedback and adjustment mechanisms across different BC forcing levels. These results are the first to show that liquid fueled rockets emitting BC can cause global ozone depletion to a similar degree as solid fueled rockets emitting chlorine. The amplitude of the model response to 30 and 100 Gg yr^-1 emission shows that the stratosphere is more sensitive to moderate levels of BC injection than previously thought. Stratospheric particle pollution could play a significant role in future global climate change and ozone depletion.