The rise in global surface temperature has averaged more than 0.15 °C per decade since the mid-1970s. Warming has been unprecedented in at least the last 50 years, and the 17 warmest years have all occurred in the last 20 years. This does not mean that next year will necessarily be warmer than last year, but the long-term trend is for rising temperatures.
A simple mathematical calculation of the temperature change over the latest decade (1998-2007) alone shows a continued warming of 0.1 °C per decade. The warming trend can be seen in the graph of observed global temperatures. The red bars show the global annual surface temperature, which exhibit year-to-year variability. The blue line clearly shows the upward trend, far greater than the uncertainties, which are shown as thin black bars. The recent slight slowing of the warming is due to a shift towards more-frequent La Niña conditions in the Pacific since 1998. These bring cool water up from the depths of the Pacific Ocean, cooling global temperatures.