The Little Ice Age - the centuries-long period of cooling that began in the Middle Ages - appears to have been triggered by four massive volcanic eruptions in the tropics.
The deep oceans can absorb enough heat to mask the effect of global warming for a decade at a time, say scientists at the National Center for Atmospheric Research (NCAR).
A three-year series of research flights from the Arctic to the Antarctic comes to an end this week, completing an unprecedented survey of greenhouse gases in the atmosphere.
If climate change continues, summer sea ice in the Arctic could disappear altogether - but in the meantime Arctic ice could temporarily stabilize or even increase.
A new study from the National Center for Atmospheric Research and other bodies aims to quantify the effects of population growth on carbon dioxide emissions, and concludes that it could make a big difference.
Strange circular holes in clouds which have frequently led to speculation about UFOs are caused by nothing more mysterious than aircraft, a study has shown - and they can cause several inches of snow or rain too.
The Asian monsoon is sending pollutants up to stratospheric heights and spreading them right across the globe, says the National Center for Atmospheric Research (NCAR).
