Have you discussed
terra preta de Indio yet? When I first read about Terra preta and how it is still productive, after hundreds of years, I thought it was sheer genius. Keep some of that valuable carbon in your soils, rather than letting it go fertilize elsewhere. Fighting to protect reefs, oceans, forests and wetlands is something anyone can do.
I have started a thread, it is in my signature. Terre preta (biochar) is in that thread. It is a bit more complicated than you might suppose though. I have experimented with it a bit. Mixed results. The research on it is promising, but hardly mature enough to get consistent results, and certainly not something most individual people could do much about except maybe in a garden, if they have the space.
The second part of you post about reefs oceans forests etc.... Is all good from a policy viewpoint, and agricultural practices certainly have the largest impact on all those things. But again, most individuals are consumers of agricultural products, not producers. They have limited influence except maybe in political influence with their vote.
Lastly regarding Fossil fuels. I personally think it is just as big a fallacy to downplay the fossil fuel effect on the environment as it is to downplay the agricultural effect. To solve the problem BOTH have to be addressed in equal parts. Stop all fossil fuel use tomorrow, and we will still have AGW and still have environmental degradation. Fix agriculture tomorrow, and we still have AGW and climate change. But address both simultaneously (without completely eliminating the bad effects from either 100%) and you can generate a positive feedback that regenerates the land.
This is because the problem with AGW is a carbon
cycle. It is not just what gets put in the atmosphere, it is also what gets taken out by our ecosystems. Working on either side alone (or primarily) is doomed to fail, in my opinion. However, it is true the the most immediate and fixable side is the environmental side. I personally think if the environmental side was addressed, the urgency for the fossil fuel reductions would be dramatically less. One of the great things about carbon in the soil (both living and in various stages of decomposition) is that it mitigates the adverse effects of climate change dramatically. Won't necessarily stop it, but the drought, storms, floods, etc....are all moderated by functioning healthy biological systems.
That is also the biggest fight I have had on these forums by far. Nearly all the AGW posters on this forum and even in other AGW discussions have focused almost entirely on FF use, and largely ignore the greater damage to the environment caused by agriculture. Ironically, agriculture is by far easier to fix, at least from a technology POV. But it does require regulatory, infrastructure and educational changes that society seems to be resisting very stubbornly.
IMO the only way an individual can fight that is with their shopping dollars. If it concerns you, and you know it is harming the environment, don't buy it. Economics is a powerful tool. Think about just one product. Dolphin safe tuna. People refused to buy tuna unless it was labeled dolphin safe. If no dolphin safe tuna was available, they simply went without tuna. The other tuna wouldn't sell at any price. Overnight that one small issue was largely corrected. If people refused to eat CAFO products, overnight millions of acres of deteriorating cropland would be put into pasture and begin to regenerate the soil. That cover on the soil would reduce erosion, reduce pesticide, herbicide, insecticide, haber process nitrogen use and runoff into our waterways and wetlands. The dead zones in our oceans would have a chance to recover. All of which have an effect on AGW. The chain of events and trophic cascades that single act would start really isn't calculable, but it certainly would be positive.