Century-end effects of global warming will be nigh-apocalyptic (if they occur at all).
A maximum sea level rise of 216-230 feet is projected if all ice caps fully melt. Even if the ice caps only partially melt, sea level rise is likely to be much closer to the nightmare 10+ foot scenario.
Most cities were only planning for 3-6 inches in the 90's and early 2000's. Now, 3-5 feet is increasingly accepted as the lower-bound:
If true, almost all major coastal cities and population centers will be underwater by end of century. And, those that aren't will be wracked by super-storms unlike anything yet experienced.
Sadly, planting trees will likely, by itself, by an ineffective solution (though it's almost certainly something that should be done on a more limited scale).
An estimated 1.2 trillion trees would need to be planted (covering a full 11% of the landmass of the earth).
Planting trees is great for many reasons (growing locally sourced food, decreasing air pollution, strengthening biome diversity, and reducing air pollution).
The studies above didn't include covering urban spaces (think Alderaan versus Cyberpunk) like roofs or walls. If those were also used to support green reforestation/vegetation efforts, it might help reduce the overall landmass requirements to naturally reduce carbon buildup.
Additionally, the use of hydroponics (here, I mean oceanic systems like kelp) to organically capture carbon will likely be valuable given the new coastlines likely to emerge, to shore up failing food supplies, and provide alternative fuel sources.
I also think the use of advanced vertical structures (exhibiting novel geometric and topological features) might help. Might we build green skyscrapers exclusively used for tree or vegetation cultivation (as found in Singapore)?
Carbon can now be extracted directly from the air through artificially-induced carbon filtering:
i. Direct Air Capture, Global Thermostat remove carbon from the air passively.
ii. 40 million trees equivalent - 30,000 installations required.
iii. Not constrained by height - can go massively vertical saving land area.
iv. Can use carbon nano-tubes to build super strong and super tall structures.
Mirrors have been around since antiquity.
They've recently been combined with machine learning and promise to dramatically reduce carbon emissions for a range of industries.
Essentially, artificial intelligence is used to capture the optimal amount of sunlight so that thousands of giant mirrors of them are coordinated in focusing sunlight onto a fixed water source (generating an enormous amount of steam).
This steam moves giant turbines generating MW of power (with steams as the only byproduct - which returns to the earth as rain).
i. Concentrated solar power has even less CO2 production than solar voltaic.
ii. Mirrors can be sustainably manufactured since they required directed heat on sand to produce liquified silicates.
i. Directed concentrated solar power (mirrors) can be used for a wide variety of general manufacturing purposes too.
ii. Replacing traditional steel, cement, cooking, and other heat-based processes.
Mirrors can be sustainably made and used to transmit power (via light) in addition to wires and in addition to their capacity to focus light on a source.
Therefore, using mirrors to capture and direct sunlight has some significant advantages:
There's another exciting use that just became a plausible reality. Perfect mirrors have recently been developed that have nearly 0% light absorption or loss.
As a consequence, mirrors can now be chained to (continuously) reflect from areas where sunlight is abundant (daytime, high-elevation, no obstructions, etc.) to areas where it's less so, and dynamically.
This suggests that a future where solar energy transmission is continuous (uninterrupted), sustainable, and nearly perfectly clean is already upon us (though the logistical hurdles to implement such a process are potentially staggering).