Email j.m.weber@reading.ac.uk
I am interested in the chemical composition of the atmosphere, how it is changing and the role this will play in future climate change. I am also interested in interaction between atmospheric composition and climate change mitigation solutions - how will these solutions affect atmospheric composition (could there be unintended consequences?) and, flipped around, how might the composition of the atmosphere influence the effectiveness of these solutions?
My current research interests involve the climatic effect of two widely proposed climate change mitigation solutions - tree planting and enhanced rock weathering (ERW) - via their impact on atmospheric composotition.
Expansion of tree cover will increase atmospheric CO2 removal by uptake of carbon into the terrestrial biosphere but it will also lead to other climatically-relevant changes.
Trees are typically less reflective (lower albedo) than grassland which means expansion of forests will reduce the amount of solar radiation reflected back to out from the atmosphere to space, causing a warming effect.
Trees also emits large quantities of biogenic volatile organic compounds (BVOCs) such as isoprene and monoterpenes. These molecules react chemically in the atmosphere and, in doing so, increase the abundance of the greenhouse gases methane and, in most cases, tropospheric ozone. The chemical reactions of BVOCs can also lead to the production of organic aerosol. These are tiny particles in the atmosphere which can scatter solar radiation and affect cloud properties. Thus the chemistry of BVOCs can have important consequences for the energy balance of the atmosphere (solar energy in - total energy out) and so climate.
I examine the impact of changes to surface reflectivity and atmospheric composition by running computer model simulations where tree cover is expanded in regions where it is believed trees would thrive. These changes in tree cover affect the emissions of BVOCs and surface reflectivity and I compare the climatic impact of these changes to simulations where tree cover is not expanded while also factoring in the extra CO2 removal in the tree expansion case. This provides a more compressive assessment of the effectiveness of wide-scale tree planting as a method to tackle climate change.
ERW is a proposed method to remove atmospheric CO2 via the reaction of dissolved CO2 (as carbonic acid) with silicate rocks. ERW also reduces the emissions of nitrous oxide (N2)O) from agricultural soils. N2)O is a potent greenhouse gas (c. 300x stronger than CO2) but also plays an important role in stratospheric ozone (O3) concentration. Stratospheric O3 is vital to life as it reduces the amount of high frequency harmful radiation which reaches the Earth’s surface. The effect of sustained reductions to N2O emissions remain uncertain as N2O acts as a source of NOx(= NO + NO2) which destroys O3 directly but also reacts with other O3-destroying molecules such as ClO, locking them up in reservoir species (e.g. ClONO2) which don’t destroy O3.
O3 destruction: NO2 + O3 -> O2 + NO2
Reservoir formation: NO2 + ClO + M -> ClONO2 + M
These competing processes will vary in importance over time as the stratospheric burden of chlorinated molecules falls (due to the banning of their emissions in the Montreal Protocol) and wider stratospheric conditions (temperature, methane concentration etc) evolve. Therefore, to determine the effect of such N2O emission reductions, computer simulations capturing all these factors and their change over time are required. I am performing such simulations in UKESM to assess the impact of N2O emission reduction. I am also consider how external factors (whether humanity follows high or low warming future scenarios) will influence the result - would N2O emission reductions have more of an effect if pursued alongside other measures to mitigate climate change or the reverse?