George Monbiot is right to tell biochar enthusiasts to calm down. Some of us have been guilty of febrile proselytising for this most unlikely scheme for geo-engineering. It is often thus: it is only after a period of reflection and assessment that some of the disadvantages of a new weapon against climate change become apparent.

Nevertheless in his eagerness to get us to tone down our enthusiasm he goes too far. Biochar is a useful and important way to help reduce atmospheric concentrations of CO2.

First of all, let's ask why small knots of dedicated people have been focusing on biochar for the past five or 10 years. Biochar looks as if it is a cheap and highly beneficial way of disrupting the global carbon cycle.

As plants grow, they naturally absorb carbon dioxide, only to give it back as they die and then rot away. Huge volumes of carbon are continuously moving between the soil, plants and the atmosphere, dwarfing the emissions from the burning of fossil fuels. If instead of letting plant matter rot, it is turned into charcoal which is almost pure carbon and stable for many centuries, we are reducing atmospheric concentrations of CO2.

No one disputes the basic science, even George. If we can get this to work on a large scale, we can make a significant difference to greenhouse gas levels. We will have to take the organic outputs of large areas of land in order to achieve this and Monbiot is right to express horrified disbelief at some of the figures that we have suggested.

Here we depart from the path of agreement. Monbiot mentions but then ignores the other benefits of biochar. These are at least as important as direct climate change mitigation. First, soil dosed with charcoal can substantially improve agricultural productivity. Food crops grow better. Trees planted in biochar often have better root systems. Crop yields are improved. This means that we can provide food supplies for more people from a smaller area of land. Growing bigger plants and trees, which are largely made from carbon, hydrogen and oxygen has a secondary effect of holding back CO2 that would otherwise be in the air. It is another form of useful carbon sequestration, albeit a once-only gain, adding to the primary effect of storing charcoal in the soil.

The second effect of biochar is to reduce the emission of other greenhouse gases, such as nitrous oxide and methane, from the soil. Thirdly, conventional fertilisers added to biochar appear to be much more effective and less likely to be washed away. Biochar-dosed soil therefore maintains its fertility better.

No one argues that biochar's effects are well understood. Scientific investigation is only just beginning. Next month sees the publication of Biochar for Environmental Management, a book edited by Johannes Lehmann and Stephen Joseph, two of the world's pre-eminent scientific advocates of biochar. This 400-page book is not the work of gullible fools, it is a resolutely serious attempt to tell the world of the many uncertainties surrounding how best to make and apply biochar.

Its chapters on climate change mitigation are not an attempt to minimise the problems but rather to offer realistic and practical ways of utilising biochar's beneficial properties for the good of the planet and its poorer people. Yes, we don't yet understand fully why biochar works but this is not an argument to ignore it or rule it out. I challenge George to read the science in this book and then tell us whether he is quite so sceptical as he is today.

• Chris Goodall is the author of Ten Technologies to Save the Planet