Substantial and sustained reductions in greenhouse-gas (GHG) emissions are required to limit the escalating warming of the planet, the authors of the latest report from the Intergovernmental Panel on Climate Change (IPCC) conclude
Thomas Stocker, co-chair of working group I, which produced the report, said: “As a result of our past, present and expected future emissions of carbon, we are [locked into] climate change, and the effects will persist for many centuries even if emissions stop. Continued emissions will cause further warming and changes in all components of the climate system.”
The report is the first of four that will be published by the IPCC over the next year as part its fifth assessment of climate science and is based on 9,200 peer-reviewed papers. It describes the warming of the Earth’s climate system as “unequivocal”, and says many of the observed changes are unprecedented over millennia.
Human influence on the climate system is clear, with human activities extremely likely to have been the dominant cause of the observed warming since the mid-20th century, conclude the scientists. They confirm that each of the past three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850, with concentrations of CO2 increasing by 40% since pre-industrial times, primarily from fossil fuel emissions.
The document includes projections of climate change based on a new set of four scenarios of future GHG concentrations. Projections for changes in global surface temperature by the end of the century range from 0.3°C to 4.8°C compared with 1985–2003 levels. The report notes that warming over land will be greater than over the ocean.
Governments have pledged to limit temperature rise to 2°C to avoid potentially dangerous consequences, and the report makes it clear that staying below that threshold will mean leaving large amounts of fossil fuels in the ground. To stay below 2°C total global emissions must not exceed 1,000 gigatonnes of carbon (GtC), warns the IPCC. By 2011, 531 GtC had already been emitted.
“Without immediate reductions in global emissions of GHGs, the world will not be able to achieve the political target of limiting the increase in global mean surface temperatures to 2°C, but rather we are likely to see an increase of 3°C–5°C,” commented Professor Robert Watson, director of strategic development at the Tyndall Centre for Climate Change Research. “Time to act is running out if we are to take the threat of human-induced climate change seriously.”
Headlines from the IPCC report
- Each of the past three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.
- Levels of greenhouse gases in the atmosphere are unprecedented in the past 800,000 years.
- Concentrations of CO2 have risen by 40% since pre-industrial times, primarily from fossil fuel emissions.
- In the northern hemisphere, 1983–2012 is likely to have been the warmest 30-year period in the past 1,400 years.
- Human influence has been detected in warming of the atmosphere and the ocean; in changes in the global water cycle; in reductions in snow and ice; and in global sea level rise.
- Ocean warming accounts for over 90% of the energy accumulated in the climate system in 1971–2010.
- The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia. Sea level rise will be between 26cm and 82cm by 2100.
