Food insecurity in the Sahel region of Africa has almost doubled in the space of a year, with a staggering 20 million people now at risk, according to the UN Office for the Coordination of Humanitarian Affairs (OCHA). While conflict in the area is a contributing factor, the real culprit is climate change.

In its efforts to resolve the crisis, the UN is attempting to raise US$ 2 billion – the sort of gargantuan bill we are going to see in increasing frequency unless governments finally get serious about global warming. It’s not just in developing countries; food insecurity can affect everyone on the planet.

Climate change can be a tricky concept to grasp. There are so few specifics and so much uncertainty. It’s difficult to predict what will happen, especially on a regional scale. We find ourselves talking about averages when, in fact, the devil is hiding in the detail.

So what do we know? As semi-arid areas become less productive, and cold zones more temperate, food-producing zones will shift towards the poles. The global food system will reshape and redistribute.

As for the weather, there will be more variation from place to place, season to season – and even year to year – than there is today. The rise in temperature won’t be gradual or even; rather than a smooth curve, it will be more like a child’s scrawl.

First, there’s the heat. Temperature variability is increasing twice as fast as average temperatures are rising. Even if we stall average global temperatures at 2 degrees Celsius by the end of the century, a hot summer in 2100 would still be up to 5 degrees hotter than now. Alarmingly, if average warming reaches 4 degrees by the end of the century, the summer of 2100 could be as much as 8-10 degrees hotter.

We are well aware of the damage wrought by heat waves. In France and Italy, the summer of 2003 was only about 3.5 degrees hotter than last century’s average, but yields of staple crops declined by 20-30%. Drought can compound the problem. Professor Tim Benton, a champion of food security based at Leeds University in the United Kingdom, warns that average maize and soy yields in the US will decline by as much as 80% in this century.

The heat will also shift and expand the range of animal, insect and plant diseases. A warm winter followed by a hot spring and summer would spawn multiple generations of insects, increasing the potential damage to plants, crops and people.

Then there’s the rain. While dry places will become drier, rainy regions will become wetter. As we’re seeing in the UK at the moment, extreme rainfall can cause problems for farmers – degrading soil, complicating planting and harvesting, and flooding crops.

But the main challenge of the weather will be its unpredictability. Farming, which is based on the seasons, is going to get much harder. Farmers will have to plan for flood and drought at the same time. Year-to-year variations in rainfall, and therefore yields, will lead to price increases and market volatility. In turn, instability in food prices may lead to social unrest – after all, food-price rises were blamed for riots in 30 countries between 2008 and 2010, and identified as one of the major causes of the Arab Spring.

Is this unpredictability the answer to what happened in the Sahel – where the number of people facing food insecurity doubled from 11 to 20 million in a single year? It seems an astounding jump now, but over the coming years it may be something we get used to.

Increasing requests for aid from the UN are just the beginning. As food production becomes ever more fragile and fragmented, the world’s poor will become hungrier – and angrier. Governments need to act now on climate change, or face the consequences.

Read more blogs on the environment.

Author: Jane Burston is Head of the Centre for Carbon Measurement at the National Physical Laboratory in the United Kingdom.

Image: A man guards sacks of food at a food distribution centre on June 18, 2013. REUTERS/ Mohamed Nureldin Abdallah