Greenhouse gas emission reduction targets

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Greenhouse gas emission reduction targets are commonly expressed in either parts per million of carbon dioxide equivalent, parts per million of carbon dioxide equivalent concentration, a percentage reduction from a specified baseline year or by a nominated year, or in terms of limiting global climate change to below a specific temperature, such as a 2 degree increase over pre-industrial temperatures.

While carbon dioxide accounts for approximately 77% of all human greenhouse gas emissions, other greenhouse gases have different influences on global warming due to their radiative properties and lifespans in the atmosphere. The term "carbon dioxide equivalent concentration" is used to refer to the concentration of CO2 "that would cause the same amount of radiative forcing as a given mixture of CO2 and other forcing components."[1]

It is worth nothing that media coverage tends to refer to carbon dioxide emissions while more policy-oriented publications often refer to both carbon dioxide concentrations and CO2-equivalent concentration. While the Kyoto Protocol set 1990 as the benchmark year for which agreed emissions reductions were to be measured against, the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) calculated emissions reductions targets against 2000 as the benchmark year. Due to the uncertainties about what temperature increase a given carbon dioxide concentration will result in, some groups -- such as the European Union -- express their targets as aimed at keeping the increase in temperature at below 2 degrees centigrade above pre-industrial temperatures.

Existing Greenhouse Gas Emission Concentrations

In its 2007 Fourth Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) states that that "human activities result in emissions of four long-lived GHGs: CO2, methane (CH4), nitrous oxide (N2O) and halocarbons (a group of gases containing fluorine, chlorine or bromine)." The IPCC states that:[2]

  • Carbon dioxide concentration has increased from a pre-industrial of 280 parts per million to 379 parts per million in 2005 with an average annual increase over the 1995-2005 period of 1.9 parts per million;
  • Methane concentration has increased from a pre-industrial value of about 715 parts per billion to 1774ppb in 2005. The IPCC states that "growth rates have declined since the early 1990s, consistent with total emissions (sum of anthropogenic and natural sources) being nearly constant during this period";
  • nitrous oxide concentration has increased from a pre-industrial level of "about" 270 parts per billion to 319 parts per billion in 2005; and
  • "many halocarbons (including hydrofluorocarbons) have increased from a near-zero pre-industrial background concentration, primarily due to human activities."

(It is important to note that while the title of the Fourth Assessment Report refers to "Climate Change 2007", it primarily relies on data from 2005 and earlier due to the long lead times of the drafting process. The 2007 referred to in its title is the publication date).

In September 2008, the Carbon Disclosure Project reported that atmospheric CO2 concentration had reached 383 ppm in 2007 and grew by 2.2 ppm that year, which is above the 2.0 ppm average for the period 2000-2007. The authors also noted that the growth rate of emissions from the burning of fossil fuels and cement was 3.5% per year for the period of 2000-2007, "an almost four fold increase from 0.9% per year in 1990-1999." This, the authors wrote, "exceeded the highest forecast growth rates for the decade 2000-2010 in the emissions scenarios of the Intergovermental Panel on Climate Change, Special Report on Emissions Scenarios (IPCC-SRES). This makes current trends in emissions higher than the worst case IPCC-SRES scenario."[3]

Modeling Future Greenhouse Gas Concentrations and Stabilization Scenarios

In its 2007 report, the IPCC modeled six scenarios for greenhouse gas emissions ranging from the lowest of 350-400 parts per million of carbon dioxide at the time of stablization through to 660 to 790 parts per million of carbon dioxide at the time of stablization.[4]

Scenario Co2 Concentration at Stabilization Co2 equivalent Concentration at Stabilization including GHGs and aerosols Peaking year for Co2 emissions Change in global emissions in 2050 (percent of 2000 emissions) Global average temperature increase above pre-industrial at equilibrium using 'best estimate' climate sensitivity Global average sea level rise above pre-industrial equilibrium from thermal expansion only
parts per million (a) parts per million (b) year percent degrees Centigrade metres (c)
I 350-450 445-535 2000 - 2015 -85 to -50 2.0 to 2.4 0.4 to 1.4
II 400-440 490-535 2000 - 2020 -60 to -30 2.4 to 2.8 0.5 to 1.7
III 440-485 535-590 2010-2030 -30 to +5 2.8 to 3.2 0.5 to- 1.9
IV 485 - 570 590-710 2020 - 2060 +10 to +60 3.2 to 4.0 0.6 to 2.4
V 570-660 710-855 2050-2080 +25 to +85 4.0 to 4.9 0.8 to 2.9
VI 660 - 790 855-1130 2060-2090 +90 to +140 4.9 to 6.1 1.0 to 3.7

a) Atmospheric CO2 concentrations were 379 parts per million in 2005.
b) The IPCC notes that "the best estimate of total CO2-eq concentration in 2005 for all long-lived greenhouse gases is about 455 parts per million."
c) The IPCC states that "equilibrium sea level rise is for the contribution from ocean thermal expansion only and does not reach equilibrium for at least many centuries. These values have been estimated using relatively simple climate models ... and do not include contributions from melting ice sheets, glaciers and ice caps. (emphasis added)

Scientific Doubt about The Desirability of the IPCC's Lowest Emission Scenario

In June 2008, a paper in the Open Atmospheric Science Journal with James Hansen as a lead author, reviewed possible emission reduction targets and scenarios. [5] In the paper the authors noted that the European Union have adopted 2 degrees as the maximum limit before potentially triggering dangerous climate change and Hansen himself had previously suggested that limiting the increase over pre-industrial temperatures to less than a 1.7 degrees was necessary to "avoid practically irreversible ice sheet and species loss". Achieving the 1.7 degrees target -- a one degree over the warming that had already occurred by 2000 -- Hansen had calculated in 2007 required a maximum carbon dioxide concentration of approximately 450 parts per million.[6]

However, in their 2008 paper Hansen and his co-authors concluded "our current analysis suggests that humanity must aim for an even level" of greenhouse gases. They concluded "that the long-term CO2 limit is in the range 300-500ppm for 25 percent risk tolerance, depending on climate sensitivity and non-CO2 forcings. Stabilizing atmospheric CO2 and climate requires that net CO2 emissions approach zero, because of the long lifetime of CO2." They also concluded that the current atmospheres carbon dioxide concentration of 385 parts per million "is already in the dangerous zone." In particular they outlined that the lag between co2 concentrations and climate change are delayed due to the slow response times of the ice sheets and the oceans and that the loss of Arctic sea ice and the West Antarctic ice sheet "are examples of potential tipping points". They also noted that carbon dioxide was approximately 450 parts per million plus or minus 100 parts per million "when Antarctica glaciated, and that glaciation is reversible".[5]

"Humanity today, collectively, must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate. If we stay our present course, using fossil fuels to feed a growing appetite for energy-intensive life styles, we will soon leave the climate of the Holocene, the world of prior human history. The eventual response to doubling pre-industrial atmospheric CO2 likely would be a nearly ice-free planet, preceded by a period of chaotic change with continually changing shorelines. Humanity’s task of moderating human-caused global climate change is urgent," they concluded.[5]

"Paleoclimate evidence and ongoing global changes imply that today’s CO2, about 385 ppm, is already too high to maintain the climate to which humanity, wildlife, and the rest of the biosphere are adapted. Realization that we must reduce the current CO2 amount has a bright side: effects that had begun to seem inevitable, including impacts of ocean acidification, loss of fresh water supplies, and shifting of climatic zones, may be averted by the necessity of finding an energy course beyond fossil fuels sooner than would otherwise have occurred," they stated. While acknowledging that "although a case already could be made that the eventual target may need to be lower" they cautiously adopt an objective of reducing atmospheric carbon dioxide to 350 parts per million.[5]

In assessing how to achieve what is currently considered to be at the outer edge of what is under consideration in the post-Kyoto Protocol negotiations, Hansen and his colleagues propose an immediate phase out of coal-fired power stations unless they sequester their carbon dioxide emissions, changes to agricultural and forestry practices and policies to cut non-Co2 greenhouse gas emissions. With this package of changes they suggest "it appears still feasible to avert catastrophic climate change."

"Present policies, with continued construction of coal-fired power plants without CO2 capture, suggest that decision-makers do not appreciate the gravity of the situation. We must begin to move now toward the era beyond fossil fuels. Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects. The most difficult task, phase-out over the next 20-25 years of coal use that does not capture CO2, is Herculean, yet feasible when compared with the efforts that went into World War II. The stakes, for all life on the planet, surpass those of any previous crisis. The greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable," they concluded.[5]

In September 2008 the director of the Potsdam Institute for Climate Impact Research in Germany, Professor Hans Joachim Schellnhuber, told the Guardian that the proposed greenhouse gas reduction targets were insufficient and that it may be that only a reduction on Co2 levels to the pre-industrial levels of 280 parts per million would be required to ensure a stable climate. Schellnhuber described the current negotiations, which at best aim to reach 450 parts per million, as being "a compromise between ambition and feasibility. A rise of 2C could avoid some of the big environmental disasters, but it is still only a compromise."[7]

"It is a very sweeping argument, but nobody can say for sure that 330ppm is safe. Perhaps it will not matter whether we have 270ppm or 320ppm, but operating well outside the [historic] realm of carbon dioxide concentrations is risky as long as we have not fully understood the relevant feedback mechanisms," Schellnhuber said.[7]

Debate Over Emissions Reductions Targets In Negotiations of a Post-Kyoto Agreement

In discussions over the possible content of a successor agreement to the Kyoto Protocol, some developing country negotiating blocs - such as the Least Developed Countries and the Alliance for Small Island States (AOSIS) -- have argued that specific atmospheric emission targets should be central to framing the overall agreement. Other groups, such as the European Union, have broadly agreed. Martin Khor from the Third World Network summarized opposition by some developing countries to the adoption of emission reduction targets early in the negotiations because this would then the the basis for setting a target for themselves. "For example, if the global goal is 50% reduction and the developed countries set a target of 70% for themselves, the developing countries may implicitly be asked to take on a residual cut of 30%. And this would be a much deeper cut for developing countries on a per capita basis. The developing countries are not willing to take on such an onerous target for themselves, especially when there is no confidence that the required ands promised technology or finance are forthcoming," he wrote.[8]

In the course of the COP14 conference and shortly afterwards, the emission reductions targets that had been suggested by countries and negotiating groups were:

  • the Alliance for Small Island States (AOSIS) supported the adoption of emission reduction ranges necessary to keep temperature increases to below a 1.5 degree limit (centigrade).[10] It argued that a global reduction of over 85% was required by 2050 from 1990 levels and that developed countries should cut emissions by over 40% by 2020 and 95% by 2050. It also argued that greenhouse gas concentrations should peak in 2015, tat the targets adopted must be based on the most recent scientific information and that critical thresholds for less developed countries and small island countries should not be crossed. It also argued that the funding of adaptation should be by way of grants not loans so that it was consistent with the polluter pays principle.[11]
  • the European Union, Norway, Iceland, African Nations and Chile have proposed a reduction range that would keep the temperature increase to below 2 degrees.[10] This would require a 50% reduction by 2050 compared to the 1990 base year. It also argued that developing countries should cut emissions by 25-30% by 2020 compared to the business--as-usual scenario. South Africa criticized the EU's proposed 30% cut by 2020 as being too little and challenged it to set out the scientific case for developing countries adopting a 15-30% target.
  • Japan has proposed a non-binding goal of at least a 50% reduction by 2050 and promoted its sectoral approaches proposal[12];
  • Brazil has proposed a 25-40% reduction by Annex I countries, substantial cuts by developing countries and sharing the burden based on historical responsibility and equity;[12]
  • the Maldives also supported the 350 parts per million target of keeping temperature increases to below 1.5 degrees.[13]

Articles and resources

Related SourceWatch articles


  1. Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report, Intergovernmental Panel on Climate Change, November 2007, page 14.
  2. Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report, Intergovernmental Panel on Climate Change, November 2007, page 15.
  3. "Global Carbon Project (2008) Carbon budget and trends 2007", Global Carbon Project, September 26, 2008.
  4. Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report, Intergovernmental Panel on Climate Change, November 2007, page 67.
  5. 5.0 5.1 5.2 5.3 5.4 J. Hansen, M. Sato, P. Kharecha, D. Beerling, R. Berner, V. Masson-Delmotte, M. Pagani, M. Raymo, D. L. Royer and J. C. Zachos, "Target atmospheric CO2: Where should humanity aim?", Open Atmospheric Science Journal, June 2008.
  6. J. Hansen, M. Sato, R. Ruedy, et al. "Dangerous human-made interference with climate: a GISS modelE study", Atmospheric Chemistry and Physics, May 7, 2007, pages 2287-2312.
  7. 7.0 7.1 David Adam, "Roll back time to safeguard climate, expert warns: A return to pre-industrial levels of carbon dioxide urged as the only way to prevent the worst impacts of global warming", Guardian (UK), September 15 2008.
  8. Martin Khor, "Key issues dominating the Poznan talks", Third World Network, December 1, 2008.
  9. COP 14 and COP/MOP 4 Highlights: December 1, 2008", Earth Negotiations Bulletin, Volume 12 Number 386 - Tuesday, December 2, 2008.
  10. 10.0 10.1 Christoph Bals, "Between Poznan and Copenhagen: The Climate Train in the "Valley of Death" Results of the UN Climate Summit in Poland, 1-12 December, 2008"], Briefing Paper, Germanwatch, January 2009, page 6.
  11. Martin Khor, "Parties debate "shared vision" in UNFCCC workshop", Third World Network, December 3, 2008.
  12. 12.0 12.1 "COP14 Highlights December 2, 2008", Earth Negotiations Bulletin, Volume 12 Number 387, December 3, 2008.
  13. Meena Raman, "Shared vision" debate dominates Poznan's opening plenary", Third World Network, December 2, 2008.

External articles