What is the most cost-effective solution to climate change based on scientific evidence? Please don't answer without citing scientific research which has a general consensus or article from a reputable source based on verifiable research citations.
I recently read this article about a 2017 PNAS study from Griscom et al (link below) that &quot;estimated natural carbon solutions (NCS) (essentially ecosystem regeneration) have the potential to provide up to 37 percent of the CO2 mitigation that we'd need through 2030, for a 66 percent chance of holding warming to below 2°C.&quot;
More specifically, what is the most cost-effective solution? Most geoengineering solutions have significant risks or unknowns which greatly reduce their benefit. Reducing fossil fuel use immediately will reduce short-term economic output with replacing with renewables and alternatives. Maybe simply paying drivers incentives to use alternative vehicles is most-cost effective, as transportation is the largest percentage of greenhouse gas emissions in the US (EPA).
So what is the most cost-effective and how much money would it take to get it done? Global energy-related CO2 emissions were 33.1 Gt CO2 in 2018 according the [IEA report][6]. Apparently from the Griscom study, 10 USD MgCO2e−1 is the &quot;current cost of emission reduction efforts underway and current prices on existing carbon markets&quot; from 2017. 1Gt = 1Pg = 1000Mt = 1000Tg = 10^9 tonnes metric, and 1Mg = 1 tonne, so our CO2 emissions cost us 10*10^9 or 10 billion USD per year. For reference, global GDP is at US$84.84 trillion for 2018, meaning reducing our entire emissions to zero would cost all of 0.0001% of global GDP.
As as corollary, if all benefits of NCS to uncalculated ecosystem services were included, would they be the most cost-effective, and what is the average ROI on research investment to calculate them?
To the Mods: I've changed the title to match the narrow question specified in the body of the question. I've provided an answer that is very specific using calculated figures from cited references. What else would you like to make the question more narrow?
Griscom et al, https://www.pnas.org/content/114/44/11645
In researching my question to provide what is known so far I found the following information. I won't accept my own answer unless it gets the most upvotes.

I found this ranked list from 'Project Drawdown' (PD) that states Managing Refrigerants is the number one solution by GT CO2 reduction by total, but with an unknown cost. Offshore wind turbines (OFTs) seems to be the best solution by total reduction. Electric vehicles (EVs) has the highest savings, but with also the highest cost. 

Dividing the reduction amount by the savings leads to OVTs at 11.4 GT CO2 reduction per trillion USD a year (GCR/TUY), then Solar Farms (SFs) at 7.35 and EVs at 1.11 for the top three by savings. However, if all are calculated and ranked, the most reduction by savings is Tree Intercropping at 778 and methane digesters small at 137, the most reduction by cost is Nuclear Energy at 18254 and then Solar Water at 2033, but including the costs with negative numbers (not sure what that means) it's Landfill Methane at -1374 and Solar Farms at -458 GCR/TUY.

I'm not sure if they're including the cost of nuclear accidents or waste storage, since waste storage at least in the US has not been reconciled, and may not be fast enough, so using Solar Water at 2.033 GCR/BillionUY, it would cost 16.3 billion USD per year to reduce the CO2 we emit for energy. Based on a single strategy, that's 2.11 dollars per person in the world (7.7 billion) and $12.50 for every person in the developed world (1.3 billion). Is this correct?

In the PD FAQs they state, "Carbon pricing is a policy mechanism to implement solutions and not in itself a solution to global warming. It is the single most impactful policy proposal that would accelerate the adoption of every solution enlisted."

Adding a few other solutions I've found:


CO2 recapture in concrete can reduce it's emissions by 40% (it is 8% of global) and also the energy used. https://www.solidiatech.com/
Red mud as a carbon sink, using the hydroxides from aluminum smelting because of the high solubility of CO2 in them.
Relying on rock weathering from carbonic acid in rain and because "Coccolithophores account for half of the calcium carbonate creation in the ocean", some kind of phytoplankton farms harnessing their "potential for carbon sequestration but also for the production of high value products, such as fatty acids and pigments."