The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts.
In 2013 and 2014, the IPCC released its Fifth Assessment Report (AR5) on Climate change. AR5 provides a clear and up to date view of the current state of scientific knowledge relevant to climate change. It consists of three Working Group (WG) reports and a Synthesis Report (SYR). The three WG reports cover (1) The Physical Science Basis, (2) Impacts, Adaptation, and Vulnerability, and (3) Mitigation of Climate Change.
Key Findings from the 2014 IPCC Fifth Assessment Report
Physical Science Basis
- Warming of the climate system is unequivocal. Since the 1950s, many observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.
- 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.
- Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, Arctic sea ice has decreased in extent, and glaciers have continued to shrink almost worldwide.
- The rate of sea level rise since the mid-19th century has been larger than the rate during the previous two millennia. Over the period 1901 to 2010, global mean sea level rose by 0.19m (0.6 ft.).
- The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.
- Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.
- Global temperature change for the end of the 21st century is likely to exceed 2° C (3.6° F) if emissions continue to remain high. Warming could stay below 1.5° C (2.7° F) only with drastic emissions reductions.
- The oceans will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation.
Impacts, Adaptation, and Vulnerability
- In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.
- In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality.
- Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions in response to ongoing climate change.
- Based on many studies covering a wide range of regions and crops, negative impacts of climate change on crop yields have been more common than positive impacts.
- Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires, reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability.
- Climate-related hazards exacerbate other stressors, often with negative outcomes for livelihoods, especially for people living in poverty.
- Violent conflict increases vulnerability to climate change.
- Adaptation and mitigation choices in the near term will affect the risks of climate change throughout the 21st century.
Mitigation of climate change
- Mitigation is a human intervention to reduce the sources or enhance the sinks of greenhouse gases.
- Effective mitigation will not be achieved if individual agents advance their own interests independently.
- Issues of equity, justice, and fairness arise with respect to mitigation and adaptation
- Climate policy intersects with other societal goals creating the possibility of co-benefits or adverse side effects.
- Mitigation scenarios reaching about 450 or 500 ppm CO2 equivalent by 2100 show co-benefits for cost-sharing, human health, ecosystem impacts, and sufficiency of resources and resilience of the energy system.
- Behavior, lifestyle and culture have a considerable influence on energy use and associated emissions, with high mitigation potential in some sectors, in particular when complementing technological and structural change.
- Decarbonizing (i. e. reducing the carbon intensity of) electricity generation is a key component of cost effective mitigation strategies in achieving low-stabilization levels (430 – 530 ppm CO2 equivalent).
- The most cost-effective mitigation options in forestry are afforestation, sustainable forest management and reducing deforestation, with large differences in their relative importance across regions.
- In agriculture, the most cost-effective mitigation options are cropland management, grazing land management, and restoration of organic soil.