|A smoking-cessation skeptic|
Suppose your grandmother comes into the emergency room with a severe pneumonia. Probably she should have gone to her doctor last week when she started with a wet cough and a low-grade fever, maybe a little short of breath, but she decided to tough it out. Now her respirations are shallow and fast, she is pale and sweaty, and the toxic byproducts of the bacteria in her bloodstream have stunned her heart, dropped her blood pressure and shut down her kidneys.
She's dying. What do you want the ER doctor to do?
The first option is to do what should have been done last week; prescribe some oral antibiotics, bedrest, lots of fluids. But while that's was right thing to do last week, today that therapy will accomplish exactly nothing, unless you put the nurse in your personal time machine and send him back to last week.
So we are going to come at this a little harder; we are going to treat it like the emergency it is. IV fluids to correct dehydration, IV antibiotics to tackle the infection, supplemental oxygen to give a head start to her struggling lungs.
But sometimes that doesn't work either. The blood pressure doesn't correct with IV fluids; other organs begin to fail; her lungs cannot maintain her body's oxygenation requirements, even with the supplemental O2. She is still breathing fast and shallow and now starting to have heart and liver dysfunction to go with the kidney failure.
At this point your only option(*) is critical care. A breathing tube will do what her lung muscles no longer can. Vasopressive drugs will support her blood pressure. She may need supplemental electrolytes; she may need insulin to control an elevated glucose.
An important fact to realize about critical care is that all of these interventions -- all of them -- are terrible for the body and fraught with life-threatening side effects. None of them are remotely as safe and effective as going in to see your family doctor when you(**) are coughing with a fever and shortness of breath. But, again, no time machine.
Those vasopressors will clamp down your peripheral circulation and can cause skin ulcers, gut ischemia, maybe further cardiac damage. Intubation can lead to long-term respiratory failure, barotrauma (you put too much air in the lungs!), or oxygen toxicity. The IV fluids will leak out of the vessels and cause edema, and so on.
Critical care -- all medicine, really, but especially critical care -- is a matter of trade-offs. We support your critical needs -- especially adequate and well-oxygenated blood flow to your heart and your brain -- at the expense of the normal, orderly functioning of your body. That makes them temporizing measures. Only an idiot would do these things and not also treat the underlying infection with powerful IV antibiotics. Without the antibiotics and functioning immune system, none of the other measures are likely to accomplish anything except to briefly prolong a painful death.
Geoengineering is similar to critical care. It is absolutely inferior to timely mitigation. However we have not carried out timely mitigation, and are now sitting on a massive stockpile of melting permafrost and an inefficient economic system generating huge volumes of CO2 and other GHGs with a large amount of inertia. Even if we were to embark on an ideal program of mitigation today, we would likely end up over the 2C threshold.
There is no point in geoengineering if we do not also intensively mitigate. It is bound to be at best a partial solution, with many side effects, and much more expensive than it looks on paper. Mitigation is like the antibiotics; the critical care in essence buys time for the real solution to work.
* Other than hospice, which doesn't really work with this metaphor.
** Grandmother/otherwise elderly you. If you're under fifty, it's probably just a cold, you big baby.