The effect of the Kyoto Protocol on global warming

On the Record

Tom M.L. Wigley

Now retired, Tom Wigley was an NCAR Senior Scientist when this statement was published in 2006.

Kyoto Protocol implications for carbon dioxide, temperature, and sea level


Tom Wigley in 1998 reported research showing that adherence to the Kyoto Protocol alone, without subsequent action, would have a minimal impact on global warming.

In the article, published in Geophysical Research Letters (see below), he concluded: "This does not mean that the actions implied by the Protocol are unnecessary." He called the protocol an important first step while pointing out that much more must be done after Kyoto to reduce future global warming by a significant amount.

Wigley used computer modeling to test several emissions scenarios for the "Annex B" countries—the industrialized and nearly industrialized countries called upon to reduce greenhouse gas emissions in the protocol. Each scenario was played out through 2010 (the midpoint of the Kyoto commitment period of 2008–2012) and then extended to the end of the century.

The first scenario looked at what would happen if, after the protocol expires, the Annex B countries continued to abide by Kyoto's limits but did not make any new commitments to further cut emissions for the rest of the century.

This "constant compliance" scenario would shave 0.11 to 0.21 degrees Celsius (0.20–0.38 degrees Fahrenheit) off global average temperatures by 2100. Stated another way, instead of heating up by 2.5°C (4.5°F), a midpoint in the range of projections of global warming, Earth would warm approximately 6% less.

For comparison, the study also examined a "business as usual" or "no climate policy" case. The starting point was IS92a, an emissions scenario included in the 2001 report of the Intergovernmental Panel on Climate Change, that incorporates a slight tapering off in emissions later this century due to global economic and social activities unrelated to climate change.

Wigley concluded that the impact on projected temperature increases, with all countries doing only what is required under Kyoto and then continuing with business as usual, would be a scant 0.06 to 0.11°C (0.11 to 0.20°F) shaved off the total warming, roughly a 3% reduction.

He also considered a third scenario in which the Annex B countries continue to reduce their emissions after the Kyoto period by 1% per year (a scenario that, like the other two scenarios, assumes continued growth of emissions in developing countries at a business-as-usual rate). In this case, the warming reduction by 2100 would be some 14%.

In a 2005 article in Science (see below), Wigley found that Earth is already warming due to human actions. Averting further warming will require a global reduction in human-generated greenhouse gases by all nations, developed and developing, to substantially below present levels.


Geophysical Research Letters: The Kyoto Protocol

Wigley, T.M.L. (1998), "The Kyoto Protocol: CO2, CH4 and climate implications," Geophysical Research Letters, vol. 25, pp. 2285–88.


Kyoto Protocol implications for CO2, temperature and sea level are examined. Three scenarios for post-Kyoto emissions reductions are considered. In all cases, the long-term consequences are small. The limitations specified under the Protocol are interpreted in terms of both CO2 and CH4 emissions reductions and a new emissions comparison index, the Forcing Equivalence Index (FEI), is introduced. The use of GWPs [Global Warming Potential values] to assess CO2-equivalence is assessed.

Excerpts from the conclusion

Three Kyoto Protocol cases have been examined. These extend the Protocol beyond [2010]1 by assuming no further reductions in Annex B emissions;2 constant Annex B emissions; or a decline in Annex B emissions at 1% compound per year.3

. . .

Large additional emissions reductions are required at some future date (certainly earlier than 2040) if concentration stabilization is to be achieved at 550 ppmv [parts per million by volume] or lower.
. . .

Finally, reductions in temperature and sea level rise under the Protocol and the extensions considered here are relatively small, but nonetheless important as a first step towards stabilizing the climate system. (emphasis added)



1The paper lists the date as 2100, a typographical error corrected here to 2010.

2This is the "business as usual" case.

3These latter two cases correspond to the imposition of either small or modest emissions-reduction policies, but only in Annex B countries, not globally.

Science: The Climate Change Commitment

Wigley, T.M.L. (2005), "The Climate Change Commitment," Science, vol. 307, pp. 1766–69.


Even if atmospheric composition were fixed today, global-mean temperature and sea level rise would continue due to oceanic thermal inertia. These constant-composition (CC) commitments and their uncertainties are quantified. Constant-emissions (CE) commitments are also considered. The CC warming commitment could exceed 1°C. The CE warming commitment is 2° to 6°C by the year 2400. For sea level rise, the CC commitment is 10 centimeters per century (extreme range approximately 1 to 30 centimeters per century) and the CE commitment is 25 centimeters per century (7 to 50 centimeters per century). Avoiding these changes requires, eventually, a reduction in emissions to substantially below present levels. For sea level rise, a substantial long-term commitment may be impossible to avoid.

Excerpt from the conclusion

The CE results reinforce the common knowledge that, in order to stabilize global-mean temperatures, we eventually need to reduce emissions of greenhouse gases to well below present levels.4 The CC results are potentially more alarming, because they are based on a future scenario that is clearly impossible to achieve and so represent an extreme lower bound to climate change over the next few centuries. For temperature, they show that the inertia of the climate system alone will guarantee continued warming and that this warming may eventually exceed 1°C. For sea level, a continued rise of about 10 cm/century for many centuries is the best estimate. Although such a slow rate may allow many coastal communities to adapt, profound long-term impacts on low-lying island communities and on vulnerable ecosystems (such as coral reefs) seem inevitable. (emphasis added)



4See T.M.L. Wigley, R. Richels, J.A. Edmonds (1996), "Economic and environmental choices in the stabilization of atmospheric CO2 concentrations," Nature, vol. 379, pp. 240–243.

Related Links 

For background

UN Framework Convention on Climate Change (three languages available)

         Relationship of Kyoto Protocol to UN Framework Convention

                  Text of the Kyoto Protocol (six languages available)

UN Environment Programme: Climate Change

For research

MAGICC and SCENGEN Computer Models

These coupled, interactive software suites were used in the 2001 IPCC Third Assessment Report and by Wigley for the 1998 article. The software allows experimenters to investigate future climate change and its uncertainties at both the global-mean and regional levels.


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