Climate change

Irreversible now

Print edition : November 01, 2013

(a) Observed global mean combined land and ocean surface temperature anomalies, from 1850 to 2012, from three data sets. Top panel: annual mean values; bottom panel: decadal mean values, including the estimate of uncertainty for one data set (black). Anomalies are relative to the mean of 1961-1990. (b) Map of the observed surface temperature change from 1901 to 2012 derived from temperature trends determined by linear regression.

Multiple observed indicators of a changing global climate: (a) Extent of northern hemisphere March-April (spring) average snow cover; (b) Extent of arctic July-August-September (summer) average sea ice; (c) Change in global mean upper ocean (0-700 m) heat content aligned to 2006-10, and relative to the mean of all data sets for 1971; and (d) Global mean sea level relative to the 1900-05 mean of the longest running data set, and with all data sets aligned to have the same value in 1993, the first year of satellite altimetry data. All time-series (coloured lines indicating different data sets) show annual values, and where accessed, uncertainties are indicated by coloured shading.

A lake formed by meltwater from the Patouri glacier, northern Peru, as seen from atop the glacier on September 19. A 2012 paper says it is one of the fastest receding glaciers in the Cordillera Blanca mountain range of the Andes.

Multiple observed indicators of a changing global carbon cycle: (a) atmospheric concentrations of carbon dioxide (CO2) from Mauna Loa and the South Pole since 1958; and (b) partial pressure of dissolved CO2 at the ocean surface (blue curves) and in situ pH (green curves), a measure of the acidity of ocean water. The measurements are from three stations from the Atlantic and Pacific Oceans.

Radiative forcing (RF) estimates in 2011 relative to 1750 and aggregated uncertainties for the main drivers of climate change. Values are global average RF partitioned according to the emitted compounds or processes that result in a combination of drivers. The best estimates of the net RF are shown as black diamonds with corresponding uncertainty intervals; the numerical values are provided on the right of the figure, together with the confidence level in the net forcing (VH: very high, H: high, M: medium, L: low, VL: very low). Albedo forcing due to black carbon on snow and ice is included in the black carbon aerosol bar. Total anthropogenic RF is provided for three different years relative to 1750.

The latest report from the IPCC states in stronger language than ever before that human activity has set the earth on an irreversible path to climate change, the effects of which will persist for centuries even if carbon dioxide emissions are curtailed now.
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