Is the green movement part of the problem?
Outside San Francisco, California - It is a modern miracle. There are now over 6 billion people on earth (more than double the number when I was born), yet very few go hungry. In fact, despite the vast increase in population, the world still produces more food than it consumes.
This is in large part a result of the industrial manufacture of nitrogen fertilisers. Since World War II, the increasing use of nitrogen has helped swell crop yields year after year.
But it comes at a price. It takes a vast quantity of energy, and therefore fossil fuels, to fix the nitrogen in modern fertiliser. But the biggest atmospheric impact of nitrogen fertiliser is from nitrous oxide, a by-product of fertiliser manufacture and use and itself a very potent greenhouse gas, 296 times as powerful as carbon dioxide.
In Cool Farming, a report on the climate impacts of agriculture, Greenpeace estimates that the emissions from the production and use of nitrogen fertilisers contribute the equivalent of two and a half billion tons of CO2 to the atmosphere every year.
That is the same amount as the pollution from all the power plants in the US, according to another Greenpeace report.
So you might expect that Greenpeace would welcome a new technology that could dramatically reduce the need for nitrogen fertiliser. Not so.
At a biotech company outside San Francisco I was shown a technology that could do just that. It does not look that impressive. A few rice plants huddled in the back of a growing chamber in a research lab, in a building on what, in Britain, we would call an industrial estate.
But these plants really could be revolutionary. They have been genetically engineered to be dramatically more efficient at using nitrogen than normal plants. What they are designed to do is allow farmers to cut fertiliser use dramatically while maintaining crop yields.
This is no pipe-dream. Arcadia Biosciences, the company which created these plants, says the genetic modification can be used for all the main crop species. Its research suggests crops containing its modified genes require half the fertiliser of normal plants.
Arcadia has licensed the technology to a number of big seed and biotechnology companies, and says crops containing the genetic modification will be on the market within a couple of years.
Developing nitrogen efficient plants to mitigate climate change is something Greenpeace specifically recommends in its Cool Farming report.
"The crop could have a greater water or nutrient use efficiency", the report argues, "increasing the yield at the same input, or enabling a reduction in external inputs, and the associated energy required to supply this input whilst maintaining the same yield".
However, when I discussed this technology with Rolf Skar, a senior Greenpeace campaigner, he said the organisation does not support using genetic engineering to cut carbon.
He said the technology is unproven.
"The history of GMOs [Genetically Modified Organisms] is riddled with unintended consequences and promises that have not been met," he told me.
Greenpeace has drawn up a plan for cutting emissions based on using more traditional renewable technologies, wind, solar, tide and wave power. The problem is that the plan will, as Skar says, require a huge investment of public money and the support of government.
Eric Rey, the founder and CEO of Arcadia, argues that he is an environmentalist too. He is a life-long member of the America's oldest and largest environmental organisation, the Sierra Club, and believes his genetically engineered plants are entirely consistent with his green beliefs.
Indeed, he argues that his technology is truly sustainable in the sense that it does not need any subsidy or political support. He argues that farmers will want to use his plants - and thereby reduce greenhouse gas emissions - not because they want to save the planet but out of their own self-interest.
Nitrogen fertiliser is a major expense for farmers, sometimes their main outlay. Because these new plants require less fertiliser for the same yield they will save farmers money.
Genetic engineering is a life-altering technology. It goes without saying that no genetically modified organisms should be used that pose a significant risk to health or to the environment but, I asked Skar, given the potential catastrophe of climate change, surely it is prudent to explore any technology that could cut emissions?
He told me no.
"Could be is not good enough for me", he said, "I want to know that it is actually going to work."
Is he right?