Climate Change Threatens Power Output, Study Says As the climate gets warmer, so do the rivers and lakes that power plants draw their cooling water from. And that is going to make it harder to generate electricity in decades to come, researchers report. In an article in the journal Nature Climate Change, scientists measured temperatures now and projected what they would be at midcentury. The temperatures vary according to the time of year, and, even if the extremes remain similar, they will be more frequent - meaning that the water will be too warm to allow full power production, they predict. All power plants that burn coal or split uranium, and most of the plants that burn natural gas, turn the resulting heat into steam, which spins a turbine that turns a generator to make power. Then the steam has to be converted back to water before being reheated. If the river or lake water used to condense the steam is getting warmer, the amount it can condense is reduced, leading to a decline in power output. Using computer projections of climate change possible outcomes, the researchers wrote that generating capacity in the United States could fall 4.4 to 16 percent on hot days from 2031 to 2060. And the number of days when river water is at a temperature that is now considered extremely high will be triple the number today, on average, they said. The idea of varying availability of cooling water is not new; many American steam-electric plants already have a summer power rating and a winter power rating. Extremely hot weather is not the norm today. Still, power plants have experienced the headache of cooling water shortages in the past. Some power plants in the United States shut down during a drought in 1988 because the level of water in the Mississippi fell below the opening of their intake pipes. The Electric Power Research Institute, a nonprofit utility consortium, produced a lengthy study in 1995 on the threat posed by climate change. It discussed the possibility of federal limits on carbon dioxide emissions (which 17 years later, may now be approaching) and the problem of hot cooling water. It found that in addition to making electricity harder to generate, warm weather would make peaks in electricity demand even higher. That would raise costs, it said, because utilities might need more generating stations that would run for only a few hours a year, during the peak summer demand periods. It also pointed out that if rainfall patterns changed, hydroelectric dams would be less productive. The solutions to this problem are not obvious. Wind generation might not help much, because the wind usually does not blow much in hot weather. Solar photovoltaic cells could help, but they do not generate much in the last hour before sunset, and not at all after that. That is the period in which many utilities experience peak demand, as people return home from work and turn on air-conditioners, television sets and ovens. Some generating stations have air-cooled condensers that use electrically driven fans instead of water. But that means less output of electricity - and more carbon dioxide emissions per kilowatt-hour. The researchers who wrote the article for Nature Climate Change - from Austria, the Netherlands, Germany and Washington State - pointed out that plants running on natural gas at a higher efficiency - that is, putting more of the heat into making power and less into waste that must be absorbed by water - could be helpful. Because generating plants usually last for many decades, "adaptation options should be included in today's planning,"" they wrote.