Climate change and agriculture

Hello. I’m professor Stephen Sitch, chair in climate change at Exeter University. Agriculture is a major contributor to climate change. Land conversion alone, the clearance of forests and other habitats for cropland and pasture, is responsible for a third of all human CO2 emissions to date. And it’s not just CO2, methane from cattle, rice paddies, et cetera. Nitrous oxide, which is linked to fertilizer use, are also important greenhouse gases whose concentrations have increased over the last century. Today, agricultural production accounts for over 50% of the human emissions for both gases. But not only is agriculture a key driver of climate change, it’s also one of its major victims.

Climate is already a problem for agriculture, even before we consider human induced climate change. As we heard last week, yields of crops like corn, rice, wheat, and soy have increased dramatically since the 1960s, due to the Green Revolution. But in many regions climate limits further increases in productivity, especially temperature and rainfall patterns. Climate change will amplify these challenges. The general effect of global warming is that areas suitable for rain fed crops are shifting northwards. This will result in regional winners and losers. In Europe, for example, we might see production of crops like soy and sweet corn be displaced from southern Europe to Scandinavia. Unfortunately agricultural pests and diseases are also traveling northwards.

And Exeter study identified that tropical pests are moving outwards towards the poles an average of two miles each year. The temperate regions, Europe, US, China, will be least affected by climate change. Whilst crop losses are inevitable, these may be partially offset by rising temperatures, increasing yields from some crops. Crop production could expand into areas previously unsuitable for crops. For example, high latitude cold regions. Some regions may be able to adapt. For example, by increasing use of irrigation, or switching to crop varieties with better tolerance to water or heat stress.

High income countries are most likely to be able to invest in the research and infrastructure necessary for adaptation, but significant yield losses are expected in the tropics, Africa, Asia, South and Central America, due to drought and elevated temperatures. This is already where the world’s major hunger hotspots are located, and climate change will exacerbate the problem. Staple crops like wheat, maize, rice are especially vulnerable. A recent study in sub-Saharan Africa recorded maize yields losses of 65% with just a one degree warming. And that is one of the more heat tolerant crops. The frequency of extreme weather events is on the rise from floods to droughts, late snow and heatwaves. This presents a major challenge to agriculture.

In 2003, Europe experienced a heatwave. The average temperature that summer was only 3.5 degrees above the average for the last century, but it led to up to 36% reductions in grain or fruit yields. Climate changes effect on the composition of the atmosphere has been heralded as one of the few positive aspects of climate change. As carbon dioxide concentrations increase, plants photosynthesize more. They convert sunlight into sugars. Plants also use water more efficiently under higher CO2 levels. In theory these effects could increase grain yields by up to 20%, but studies suggest that these will be canceled out by the effect of heat stress. So that introduces some of the impacts of climate change in agriculture.

You’ll find out about potential solutions in the article that follows.