The amount of greenhouse gases in the atmosphere reached a new record high in 2011 (2012 data will be available later this year). The period 1990 to 2011 saw a 30% increase in radiative forcing – a measure of the warming effect on the climate – because of increased atmospheric concentrations of greenhouse gases.
Carbon dioxide (CO2), the single most important greenhouse gas emitted by human activities, is responsible for 85% of the increase in radiative forcing over the past decade (water vapour is also a powerful GHG but human activities affect its levels indirectly). The amount of CO2 in the atmosphere reached 390.9 parts per million in 2011, or 140% of the pre-industrial level of 280 parts per million.
Methane (CH4) is the second most important long-lived greenhouse gas. Atmospheric methane reached a new high of about 1813 parts per billion (ppb) in 2011, or 259% of the pre-industrial level, due to increased emissions from man-made sources. Since 2007, atmospheric methane has been increasing again after a period of levelling-off, with a nearly constant rate during the last three years.
Nitrous oxide (N2O) is emitted into the atmosphere by both natural (about 60%) and man-made sources (approximately 40%), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. Its atmospheric concentration in 2011 was about 324.2 parts per billion, which is 1.0 ppb above the previous year and 120% of the pre-industrial level.

Global temperatures continue to climb.

The global average temperature is estimated to have risen by 0.6 C (1.1 F) over the course of the 20th century. Although the rate of warming varies from year to year due to natural variability such as the El Niño cycle, volcanic eruptions, and solar variations, the human-induced warming trend has clearly continued.

2001-2010 was the warmest decade on record since modern temperature monitoring began around 160 years ago. The global combined land-air surface and sea-surface mean temperature for the decade is estimated at 0.47°C (0.8°F) above the 1961-1990 average of 14.0°C (57.2°F). Globally, 2010 is estimated to be the warmest year ever recorded since modern measurement began, closely followed by 2005. No single year since 1985 has recorded a below-average mean.
The 2001-2010 decade was also the warmest ever recorded for each continent. Average temperatures above the 1961-1990 level dominated every continent in every year of the decade, with the exception of Australia in 2001. Europe and Asia recorded the largest average temperature anomaly for the decade (+0.97°C), while South America recorded the lowest decadal temperature anomaly among the continents (+0.41°C).
2011 was an estimated 0.40°C (0.72°F) above the 1961-1990 average and the warmest-ever year that featured a cooling La Niña event. 2012 was the ninth warmest year since records began in 1850. The global land and ocean surface temperature for the year was about 0.46°C (0.83°F) above the corresponding 1961–1990 average of 14.0°C. After the end of the La Niña in April 2012, the global land and ocean temperatures rose increasingly above the long-term average with each consecutive month.12 In January 2013, NOAA and NASA announced that 2012 was the warmest year on record for the United States.

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Sea levels are changing globally.

The upper layers of the oceans expand as they heat up, while water from melting glaciers and ice caps add to the volume of the sea. Local variations in currents and in land movement mean that the rise in sea levels is not uniform, so some coastal regions are more affected than others. As warming penetrates deeper into the oceans and ice continues to melt, sea levels will continue to rise long after atmospheric temperatures have levelled off.
The rate of increase of global mean sea levels over the 2001-2010 decade, as observed by satellites, ocean buoys and land gauges, was some 3.2 mm per year, double the observed 20th century trend of 1.6 mm per year. As a result, global sea levels averaged over the decade were about 20 cm (8 inches) higher than those of 1880.20 Sea levels are projected to rise by a further 28-58 cm (11-23 inches) (compared to 1989-1999 levels) over the course of the 21st century; the higher end of this range would cause enormous damage to cities and other coastal settlements, infrastructure and ecosystems. Even higher levels could occur if the ice caps melt at a more rapid pace. 21 Estimates of future sea-level rise continue to be assessed and will be updated by the next IPCC report in September 2013

UNEP 2012