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Rice is arguably the world's most important food source and helps feed about half the globe's people. But yields in many areas will drop as the globe warms in future years, a review of studies on rice and climate change suggests.

The poorest parts of the world, including Africa, will probably be hardest hit, the study says. Rice harvests already need to increase by about a third just to keep up with global population growth.

Predicting how a changing climate will affect crop yields is notoriously difficult. Temperature, carbon dioxide concentration and ozone levels all have a big impact on growth. Yet most studies look at just one of these factors, making it difficult to know what the combined effect will be.

It is also hard to know whether results from experiments in greenhouses with artificial climates will hold true in the real world. But when the evidence from some 80 different studies is combined, the outlook is bleak, says Elizabeth Ainsworth of the University of Illinois, Urbana-Champaign.

Last month's lunar eclipse not only treated skygazers to a ruddy view of the Moon – it revealed that Earth's atmosphere contains little light-blocking volcanic dust.

Some researchers say the low volcanic dust levels in the atmosphere over the last dozen years could be contributing to global warming, but others dispute the claim.

During a lunar eclipse, Earth blocks sunlight from reaching the Moon directly. But some sunlight still gets through, refracted through Earth's atmosphere. The amount varies, depending mainly on how much dust from volcanic eruptions is floating around at high altitudes.

Because dust can block sunlight from passing through the atmosphere, more dust makes for a darker Moon during lunar eclipses. "All the big dimmings of the Moon during eclipses can be attributed to specific volcanoes," says Richard Keen of the University of Colorado in Boulder, US.

Keen and his collaborators have charted the brightness of eclipses back to 1960 and for a few years around the time of the 1883 eruption of Indonesia's Krakatoa volcano.

They are using the eclipse data to track changes in the opacity of Earth's atmosphere. While most of the light deflected by particles in the atmosphere is just temporarily diverted and eventually reaches the Earth's surface, the effects of atmospheric dust can have a significant, if temporary, impact on the climate, Keen says.

The release of greenhouse gases and aerosols resulting from human activities are changing the amount of radiation coming into and leaving the atmosphere, likely contributing to changes in climate.

Greenhouse Gases

Greenhouse gas concentrations in the atmosphere have historically varied as a result of many natural processes (e.g. volcanic activity, changes in temperature, etc). However, since the Industrial Revolution humans have added a significant amount of greenhouse gases in the atmosphere by burning fossil fuels, cutting down forests and other activities. Because greenhouse gases absorb and emit heat, increasing their concentrations in the atmosphere will tend to have a warming effect. But the rate and amount of temperature increase is not known with absolute certainty. Changes in the atmospheric concentration of the major greenhouse gases are described below:

Carbon dioxide (CO2) concentrations in the atmosphere increased from approximately 280 parts per million (ppm) in pre-industrial times to 382 ppm in 2006 according to the National Oceanic and Atmospheric Administration's (NOAA) Earth Systems Research Laboratory, a 36 percent increase. Almost all of the increase is due to human activities (IPCC, 2007). The current rate of increase in CO2 concentrations is about 1.9 ppmv/year. Present CO2 concentrations are higher than any time in at least the last 650,000 years (IPCC, 2007). See Figure 1 for a record of CO2 concentrations from about 420,000 years ago to present. For more information on the human and natural sources of CO2 emissions, see the Emissions section and for actions that can reduce these emissions, see the What You Can Do Section.

The Intergovernmental Panel on Climate Change and former US Vice-President Al Gore have been announced as the joint winners of the 2007 Nobel Peace Prize. They have certainly made a commendable effort in the field, but how does climate change affect the chance for peace?

The Nobel Foundation

Prizes for efforts and achievements in the fields of Physics, Chemistry, Physiology or Medicine, Literature and Peace, along with an additional prize for Economics, are awarded every year by the Swedish-based Nobel Foundation. The prizes are regarded as the most prestigious in their respective fields, with the winners receiving £750,000 cash, a medal and a diploma. Previous winners of the Nobel Peace Prize include Jimmy Carter, Kofi Annan, Desmond Tutu, Mother Teresa and Martin Luther King.

The IPCC (Intergovernmental Panel on Climate Change), which is a part of the UN, and Al Gore share the 2007 prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change".