Now, about decarbonisation plans. Did you see that Grant's got a new one? This was last week, and it's a follow-on to the Jet Zero consultation last year (which we seem to have missed). This is
the relevant DfT» page, and this
the actual report.
This should one of the easier fields for the government's concocters of plans, since the main players are big companies who already have programmes to do most of the hard stuff, and the plan just needs to pull them together and fill in the gaps.
This section may be a bit of a surprise to some:
Addressing non-CO2
Overview
3.64 Much of our Strategy focusses on how we reduce the CO2 emissions from aviation, however, we also recognise that aviation has non-CO2 climate impacts, which need to be addressed. There are large uncertainties over the magnitude of non-CO2 impacts on climate. Recent scientific evidence suggests the best estimate is that roughly two thirds of aviation’s historical climate impacts are due to non-CO2, and that, whilst non-CO2 emissions can have both warming and cooling effects, the net warming rate is likely to be around three times that of CO2.61 The uncertainties are real however: the non-CO2 impacts of aviation on climate are eight times more uncertain than those resulting from CO2.62
There was
a paper in Nature last year that goes into more detail, and has this summary of the non-CO
2 emissions and what they may do:
The formation of persistent contrails-cirrus depends on aircraft and fuel parameters as well as atmospheric conditions, as the propensity of contrail formation is higher in the cold and saturated atmosphere. Contrail-cirrus influence the incoming solar radiation and the outgoing infrared radiation emitted by the Earth and its atmosphere. The net change, the radiative forcing (RF), is on average positive and hence contrail-cirrus act to warm the climate. The emitted nitrogen oxides (NOx) react with hydroxyl radicals (HOx), which eventually form ozone and contribute to the depletion of methane in the atmosphere. Therefore, emissions of nitrogen oxides increase the ozone concentration and decrease the methane concentration (which itself leads to a reduction in ozone production and is called primary mode ozone, PMO). Ozone and methane are greenhouse gases and changes in their concentrations cause changes in the RF, which are in total positive, i.e. leading to warming. The net direct impact of aerosol emissions on RF (soot: warming and sulphate: cooling) is small and are not further regarded in this study, whereas the impact of soot emissions on contrail-cirrus properties are important and considered in our calculations (see ‘Methods’). An open question, which is currently under investigation is whether aerosol emissions significantly alter or even induce natural clouds, both low-level and cirrus clouds.
There's something about the presentation of that paper that makes me a bit suspicious, but you need to be an expert to really know if it's making sense - like how methane has a net cooling effect. But wasn't the overall effect of Covid, stopping most flights, supposed to be a net cooling - and only two years ago? (Or have I misrecollected that?)
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