IPCC releases fifth climate assessment report

31 March 2014

The United Nations’ Intergovernmental Panel on Climate Change (IPCC) has just released its fifth climate assessment report. Needless to say, the data and trends observed by the IPCC are quite worrying. Here is a short summary of the conclusions contained in the report.

What has happened so far :

Atmosphere

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years.

Ocean

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010. It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

The poles

Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

Sea level

The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia. Over the period 1901 to 2010, global mean sea level rose by 0.19 m.

Carbon

The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.

What we can expect in the next century:

Atmospheric temperature

Global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850 to 1900. Warming will continue beyond 2100 under all but one scenarios. Warming will continue to exhibit interannual-to-decadal variability and will not be regionally uniform.

Atmospheric water cycles

Changes in the global water cycle in response to the warming over the 21st century will not be uniform. The contrast in precipitation between wet and dry regions and between wet and dry seasons will increase, although there may be regional exceptions.

Ocean

The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation.

The poles

It is very likely that the Arctic sea ice cover will continue to shrink and thin and that Northern Hemisphere spring snow cover will decrease during the 21st century as global mean surface temperature rises. Global glacier volume will further decrease.

Sea level

Global mean sea level will continue to rise during the 21st century. Under all scenarios, the rate of sea level rise will very likely exceed that observed during 1971 to 2010 due to increased ocean warming and increased loss of mass from glaciers and ice sheets.

Carbon

Climate change will affect carbon cycle processes in a way that will exacerbate the increase of CO₂ in the atmosphere. Further uptake of carbon by the ocean will increase ocean acidification.

Irreversibility

Cumulative emissions of CO₂ largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO₂ are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO₂.