Let’s start with the easy question – right now we are using 11% of all the land on Earth for farming (1.5 billion ha out of a total of 13.4 billion). What percentage of the remaining 89% could be used for farming? The answer is – that depends on your definition of arable land. We can take the upper limit of the estimate of remaining arable land, and then explain why use of that land is problematic.

First, “arable” is a continuum, not a dichotomy. Some land can only be used for a very limited number of potential crops. Other land is highly suitable for many different crops. We won’t count land that is not suitable for farming, even though theoretically it could be used with extreme measures. You can grow corn in the desert, if you import all the water.

If we count all potentially arable land, it is estimated that we are currently using 36% of that land for farming. That means that 64%, or 2.7 billion ha, remain. At first this may seem encouraging, that we have lots of farmable land left. But that figure is very deceptive. Let’s dive into that 64%. The fact is we have already “picked the low hanging fruit.” We have used the best farming land for farming. What remains is largely on the low end of the continuum of suitability. If, for example, land can be used only for olive groves, that is considered arable by the above calculation.

Further, forests cover at least 45 percent, protected areas (such as wet lands) 12 percent and human settlements 3 percent, for a total of 60%. So sure, if you count cutting down rain forests, then there is lots of arable land left. If you exclude forested, protected, or settled land then we are down to 34% of arable land available for farming. This means we are currently using a little more than half of suitable arable land. But again – we are using the better half. Much of the land in the remaining half may not even be practical for use, even though it is theoretically arable.

About 90% of unused arable land is in sub-Saharan Africa and Latin America. There is a little in Asia, and virtually none in Europe or North America. Much of the arable land in Latin America is forested. So essentially, when we talk about unused suitable arable land we are mainly talking about sub-Saharan Africa. Here, again, much of this land my be technically arable (if you want to plant olive groves) but not practical.

All of this is why, at the low end of estimates, there are those who claim that we only have about 3% of arable land to expand into, which means we are using virtually all of the arable land that is practical to use without spreading into forested, protected, or settled land. To be fair, these estimates vary, because there are many assumptions and judgement calls in making the calculations. Where do you draw the line for “practical?”

Almost certainly we will need to expand the use of arable land in sub-Saharan Africa as that part of the world continues to develop. For the rest of the world, that is not a viable strategy. It is much more preferable to increase the efficiency and sustainability of farming the land already being used. In fact, ideally, we would decrease the percentage of land used for farming and return some of it back to natural ecosystems. This is a complicated issue also – it’s not as simple as letting farms go fallow, but certainly setting aside more land for butterflies and other threatened critters edged out of their ecosystems by farming would be nice.

Farmers want to be efficient and sustainable. That is best for their bottom line. Everyone’s interests here align. No one’s interests are served by poor farming practices. But there are several issues limiting optimal farming practices. One is simply the availability of technology. This is a major limiting factor in the developing world. Another is simply education – instituting best practices as quickly as possible. In every profession there tends to be a lag from scientific publication to thorough penetration of practice. In my own field of medicine that lag can be years. I don’t know what it is in farming, but there is likely some room for improvement there.

But perhaps the biggest obstacle to best farming practice is also one of the most difficult to fix – ideology. Primarily I am talking about organic farming. Not all organic farming practices are bad. The emphasis on sustainability, in fact, is a good thing. The problem is that “organic” farming is an artificial construct based on simplistic ideology, an appeal to nature fallacy on steroids. Rather than using those methods that evidence shows are best for production, the quality of the final product, and the environment, organic farming uses a fairly arbitrary list of methods that sound “natural”  while banning anything that smells too modern or technological.

This is essentially the entire basis for their banning of GMOs – genetically modified crops. They have turned being anti-GMO into a branding issue, using it to demonize their competition and enhance the health halo around their organic brand.

A recent German study finds that an organic diet uses 40% more land than a conventional diet. Estimates of land use vary by crop, but conservatively organic farming uses about 20% more land than conventional farming. By many estimates, we simply do not have the land necessary to feed the world with organic farming methods. Remember – remaining arable land that is not forested etc. is mostly less suitable than currently used land, so the crop selection would be more narrow and the production would be lower. In the end, the numbers just don’t work.

Further, as GM technology continues to progress, the gap in productivity between organic and conventional will likely grow. What if we develop wheat or corn that can fix it’s own nitrogen from the air? This would drastically reduce the need for fertilizer. Researchers are working on boosting the efficiency of photosynthesis, which could increase yields by 20% or so. Traits that reduce spoilage also reduce waste, increasing the efficiency of the food system.

Land use is the greatest factor that farming has on the environment, so methods that use more land have the most negative impact. Organic farming, therefore, is bad for the environment, and is not sustainable, even with a growing population. Don’t even get me started on the nitrogen cycle. And if you really want to worry – what effects will global warming have on the amount of arable land available?

Like many seemingly simple questions – how much arable land is there and how much are we using? – when you do a deep dive the answer may be very complex. But even taking the range of potential answers here, it seems clear that we are using most of the suitable land for farming.