If you hope we can
solve climate change
without using
Solar Geoengineering,
you’ve found your home.

See footer for scientific references

As compared to the preindustrial era, over two trillion tons of carbon dioxide have been added to the atmosphere, though half of that has been absorbed by trees and oceans. For context, a trillion tons is approximately the weight of three million Empire State Buildings.
When other greenhouse gases are included, this number is calculated as over 50 billion tons (50 gigatons) of carbon dioxide equivalent.
Note that methane has a much shorter life - around 11 years. And it does much more damage, per additional molecule, than carbon dioxide. For this reason, some scientists are focused on learning how we might remove methane from the atmosphere.
Ecosystem restoration has the potential to remove hundreds of gigatons of additional carbon dioxide over the course of many decades.
For scale, consider that the 2023 Canadian forest fires released over half a billion tons of CO2. Note that, without physical limits (of energy, water, real estate, etc), if the CDR industry achieves its goal of reducing the cost of CDR down to $100/ton, the cost to remove a trillion tons from the atmosphere would be $100 trillion. For context, the annual budget of the US government is currently just over $6 trillion. Currently, the largest Direct Air Capture (DAC) facility is being built by Occidental Petroleum, and its target capacity is half a million tons per year. (Link)
It bears noting that this sulfur dioxide, at ground level, is especially dangerous to human health.
This sulfur dioxide combined with water vapor to form sulfate aerosols in the stratosphere, which reflected sunlight until it settled back to earth over the course of the following two years.
Scientists are debating whether warming is currently crossing the 1.5 degrees Celsius threshold.
This approach is referred to as Stratospheric Aerosol Injection, or SAI. Another approach is the spraying of salt water at the surface of the ocean, in order to reflect sunlight at a more local or regional level. This is Marine Cloud Brightening, or MCB.
Only a reduction of carbon dioxide levels will reduce ocean acidification. See the work of the Ocean Acidification Alliance.