J. Geophys. Res. 113, D05115 (2008)

Credit: TROY MCCULLOUGH

Global average temperatures have risen since the mid-twentieth century, yet temperature changes aren't always apparent in day-to-day weather variability. Now researchers have found that daily extremes may also be changing.

Simon Brown at the Met Office Hadley Centre, UK, and colleagues compiled daily temperature data from land-based sites throughout the world. They found warming of both the hottest and coldest daily temperatures since 1950 for most of Europe, Asia, Central and North America, and Australia, especially during northern winter and spring months. Daily minimum temperatures have seen the biggest increases, most notably over Russia and Canada, where the coldest days are now up to 4 °C warmer than they were mid-century.

There are some exceptions — for example, warm days and nights have cooled in eastern North America — but despite these atypical locales, in general the coldest temperatures are warming more rapidly than global mean temperatures. Ultimately, this means that climate change may be most obvious in the warmer winter nights and hotter summer days to come.