It is well-established that global warming will, among other consequences, alter rainfall patterns around the world and raise sea level substantially. Estimates are that altered rainfall will bring droughts to the US southwest, southern Europe, northern Africa, and western Australia, comparable to those that caused the devastating 1930s Dust Bowl in the United States. The rising sea level will inundate low-lying islands and continental shorelines.

Now scientists at the US National Oceanic and Atmospheric Administration (NOAA) and colleagues in Switzerland and France have completed an authoritative study focusing on rainfall and the oceans. It concludes that climate change will persist for centuries, even if the nations of the world could bring carbon dioxide in the atmosphere back to the amounts of the pre-industrial era. "People have assumed that if we stopped emitting carbon dioxide the climate would go back to normal in 100 years, 200 years," said lead author Susan Solomon, a senior scientist at NOAA.  

Carbon dioxide accounts for about half the global warming caused by greenhouse gases. It is primarily removed from the atmosphere through absorption by seawater, an incredibly slow process because of the time it takes for surface water saturated with the gas to be replaced by deeper water. The slowness with which ocean water circulates is central to the new findings.

This is more bad news for anyone already concerned about the effect of global warming on the production of food and feeding the world's large and growing human population. There are some important historic examples of what to expect, and what to prepare for. 

In 2003 a record hot summer hit Western Europe between June and August. An estimated 52,000 died from heat stress, making it one of the deadliest climate-related disasters in Western history. In France, the hardest hit nation, the mean summer temperature was 3.6 degrees centigrade above the long-term mean.

Record high daytime and nighttime temperatures over most of the summer hit crops such as maize, fruit trees, and vineyards, stressed livestock, and increased agricultural water consumption. Italy experienced a drop in maize yields of 36% from a year earlier, whereas in France maize and fodder production fell by 30%, fruit harvests by 25%, and wheat harvests by 21%. These decreases in production hurt the region's farmers financially. But global food trade, subsidies, and insurance compensation combined to avert large price hikes or reductions in food security.

In contrast, extremely high summer temperatures in the former Soviet Union in 1972 had a much more disruptive effect. Temperatures in the major breadbaskets of southeast Ukraine and southwest Russia ranged from 2 to 4 degrees Celsius above the long term mean, causing a 13% decline in grain production and contributing to a sharp spike in prices between 1972 and early 1974. The shortfall prompted the USSR to buy large amounts of grain on the world market, which together with the steep price increases produced insecurity in many parts of the world, particularly Asia.

An analysis has just been published of the effect of global warming on agricultural production later in this century that uses these historical results as a basis for comparison. The authors, an atmospheric scientist and an economist, applied global climate models used by the Intergovernmental Panel on Climate Change to estimate temperatures in the future. Their results show that by the mid- to late-century the anomalously high temperatures in France and Italy in 2003 and in the Soviet breadbasket in 1972 will be the norm in large parts of the world. 

"In the past, heat waves, drought, and food shortages have hit particular regions," says author and atmospheric scientist David Battisti. But the future will be different. "Yields will be down every place." Reduced food production, and so the threat to human lives, caused by unusually high temperatures in France, Italy, and Ukraine was relieved when the temperature subsided, Extreme temperatures will persist for longer periods in the future. Furthermore, in the past surpluses in other regions allowed food to be shipped in to places that had been hard-hit. But as warming continues surpluses will be rare, if they exist at all.

These comprehensive studies stress anew the need for immediate action against global warming. It's important to minimize as much as possible the extent of the warming, even if it will be with us long into the future. The studies also underscore the need for technological improvements; development of crop varieties that are resistant to heat and of more efficient irrigation systems will help with the problem, but they won't solve it. On the other side of the ledger is the increasing pressure on the food supply as more people turn to eating meat, a trend that is expected to continue for decades. This trend represents a switch to a much less efficient way of using grain production.

The need to increase efforts against global warming and to adapt to the warming that is already inevitable will be costly. And there's evidence that it will be difficult to come up with the required funding. For example, investments to meet current food needs in the world's poorest countries have been steadily falling. Agriculture ministers from 95 countries who met a few weeks ago in Madrid called for more investments in agriculture to boost food production worldwide; without it there is a risk that production will fall. Joachim von Braun, head of the Food Policy Research Institute in Washington warned other Madrid attendees that if investment keeps dropping food supply will not keep pace with demand and could send prices soaring.

The required allocation of funds discussed in Madrid is an immediate need to fix a current problem. The longer term need to minimize the consequences of global warming will require a new way of looking at the problem, a way that is, ultimately, rooted in politics.

   
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