# The Buying Time Argument within the Solar Radiation Management Discourse
## 5 Requirements Revisited
### Desirability and Effectiveness  
According to the scenario set-up in the previous section, SAI will be successful in reducing the warming rate [38]. The authors argue that SAI will thus be able to reduce adaptation pressure, by buying more time for learning and installing different adaptation measures. Furthermore, _if_ the RCP2.6 mitigation pathway is assumed, the stabilization of temperature at \"well below 2 \({}^{\circ}\)C\" above pre-industrial level is likely to be guaranteed. Therefore, indeed, SAI deployment can be called effective support if abatement comes close to RCP2.6. Strict abatement and temporary SAI are the supportive amendments--here again we have the BTA idea. The second part of the effectiveness premise asks for a beneficial deployment. The weighting of the benefits and the negative side effects in order to guarantee some form of beneficial deployment, is a matter of dispute. It would be beyond the scope of this article to fully decide for the deployment scenarios at hand, if the benefits outweigh the costs. Whether the scenario at hand eventually is beneficial depends on model results we cannot judge. The question here is, if [PERSON]'s and [PERSON]'s deployment scenario has the theoretical conditions for the possibility of being beneficial. The beneficial requirement supposes some ideas about the beneficiaries on the one hand and about groups being put at risk by the side effects of SAI. This ratio between beneficiaries and disadvantages is to be determined and specified. Here, we enter thorny debates about the side effects of precipitation, delay of recovery of the ozone layer, acid rain, agricultural yields, migration, etc., as compared to the avoided loss and damage of climate change. Since both sides of the equation are more or less likely and speculative, the beneficial requirement remains empirically underdetermined. We leave it for further debate how BTA shall be judged if some crucial requirements remain underdetermined and speculative, resting on models. For the sake of argument, there might be situations in which a BT deployment of SAI could be more beneficial than harmful. However, this might be only the case for low-scale SAI deployment, or far less or far shorter deployment than might be desirable from a purely temperature-based assessment. As the authors of this scenario state that, \"Whatever the weighting of these benefits and cost functions, the ratio of benefits to costs will be largest for very small amounts of SRM\" [39] (p. 204). They continue to observe that \"(One) must conclude that the optimal amount of SRM will always be less than the amount of SRM that maximizes benefits\" [39] (p. 204). The authors rightly refer to the diminishing marginal utility of SAI deployment. The cost-benefit ratio of SAI deployment will be best for small amounts of SAI, which means that larger amounts will be uneconomical. This highly important conclusion should be present in any possible framing of SAI deployment. It implies that beneficial SAI deployment might be reasonable only within clear cut, very limited boundaries. Those boundaries might arguably be given in a RCP2.6 world, where emissions are cut to remain within the \"well below 2 \({}^{\circ}\)C\" budget and SAI would have to be deployed for a short period of time only. The fatal irony of BTA might be this: SAI might be legitimate only under conditions which render its deployment rather superfluous. Even then, there should be only a tiny bit of a dose. If so, a second look on costs for SAI research, testing, and deployment seems mandatory under the \"least cost planning\" approach. One could oppose this line of thinking by taking a climate portfolio (option O) into account, that also includes CDR measures, but applies to a different RCP scenario. If, for instance, in an RCP 6.0 scenario, pressure-reducing SAI is combined with concentration-shrinking CDR, SAI might well be allowed. The problem with this critique is this:  
Emission cuts, when seen as a net-sum, can also be achieved via CDR or Negative Emission Technologies (NETs).