The Role of O3 in Climate Forcing and Feedback
Ozone is an important contributor to Earth’s radiative balance. The Earth's radiation balance is directly influenced by enhanced ozone (O3) production in regions of convection, along with the longer lifetimes of O3 precursors that results from vertically transported CO. Ozone is both a major absorber of incoming UV in the stratosphere (leading to stratospheric heating) and a strong emitter in the thermal infrared. The direct radiative forcing contribution from increasing tropospheric O3 is estimated to be somewhat more than a third (and possibly as much as a half) of a W/m2 on average, resulting in a relatively small warming effect. This forcing varies from region to region depending on the amount of O3 in the troposphere at a particular location – upper tropospheric ozone has a stronger greenhouse effect than lower tropospheric ozone. The climate system is especially sensitive at the tropopause – where the troposphere meets the stratosphere.
Tropospheric O3 is also the source of the hydroxyl radical (OH), which controls the abundance and distribution of many atmospheric constituents (including greenhouse gases such as methane and hydrochlorofluorocarbons). Ozone makes a significant contribution to the radiative balance of the upper troposphere and lower stratosphere, such that changes in the distribution of O3 in these atmospheric regions affect the radiative forcing of climate.
Climate Feedback and Forcing for Tropospheric Ozone
Climate forcing by O3 remains uncertain because O3 change as a function of altitude has been under-measured. In order to better understand the role of tropospheric O3 in climate, accurate temperature measurements are needed along with co-located O3 and CO profiles. TES measurements of the vertical distribution of tropospheric O3 are used to calculate how much radiant energy is trapped by O3 at various altitudes in the troposphere.
Quantifying the Tropospheric O3 Budget
In the upper troposphere, radiative forcing is more sensitive to changes in the abundance of O3, and upper tropospheric O3 has a stronger greenhouse effect than lower troposphere O3. TES O3 data is helping to quantify this and improve our current understanding of tropospheric O3 photochemistry and long-range O3 transport.
When TES O3 profiles are assimilated into Global Coupled Chemistry Models (such as GEOS-Chem) they have an impact on radiative forcing, which is reflected in changes to the outgoing longwave radiation and temperature, and to the vertical transport and ozone distribution in the mid-troposphere. Further work needs to be done in order to fully evaluate the radiative forcing of tropospheric O3 as observed by TES. Related future work is also needed to interpret the response of tropospheric circulation to changes in temperature and outgoing longwave radiation.
Stratospheric O3
Although TES contributes measurements of O3 in the lower atmosphere, a significant fraction of the total column is above the region where TES performance becomes marginal (> 30 km). This part of the problem requires input from other instruments (e.g., MLS). Vertically-resolved O3 profiles from TES retrievals are good from the surface to the lower stratosphere.
Back: Ozone
Or, go back to: Global Climate Change
Ozone’s impact is all about location. High in the stratosphere, ozone shields us from the sun’s harmful UV rays. But beneath that, at the top of the troposphere, it acts as a greenhouse gas and contributes to global warming. In the middle of the troposphere, it plays a key role in a chemical process that cleans the air of certain pollutants. But at the bottom of the troposphere, where we live and breathe, it contributes to smog and is toxic to plants and animals. TES measurements allow scientists to track the abundance, creation, destruction, and movement of this critical chemical at various altitudes throughout the atmosphere.
