Man-Made Global Warming "Unequivocal"—What Next?

Over the weekend, the United Nations' Intergovernmental Panel on Climate Change (IPCC) released the Synthesis Report of its Fourth Assessment Report (4AR). The report is being published in advance of the upcoming 13th Conference of the Parties (COP-13) to the U.N Framework Convention on Climate Change (UNFCCC) in Bali. At the COP-13, negotiators will try to hammer out a new international treaty to deal with the man-made emissions of greenhouse gases (GHG) that are contributing to global warming. Any new treaty would replace the Kyoto Protocol which terminates in 2012. The Kyoto Protocol set a goal of reducing GHG emissions by an average of 5 percent below the level that signatory countries emitted in 1990. In October, the scientific journal Nature published a commentary that declared,

"…as an instrument for achieving emissions reductions, [the Kyoto Protocol] has failed. It has produced no demonstrable reductions in emissions or even in anticipated emissions growth."

Among other things, the Synthesis Report concludes:

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level…

Most of the observed increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.7 It is likely there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica)…

The Synthesis Report further notes:

Determining what constitutes "dangerous anthropogenic interference with the climate system" in relation to Article 2 of the UNFCCC involves value judgements. Science can support informed decisions on this issue,…

The negotiations in Bali will be over these value judgements and how to balance higher energy costs with the benefits of a cooler climate.

Impacts of climate change are very likely to impose net annual costs which will increase over time as global temperatures increase. Peer-reviewed estimates of the social cost of carbon23 in 2005 average US$12 per tonne of CO2, but the range from 100 estimates is large (-$3 to $95/tCO2). This is due in large part to differences in assumptions regarding climate sensitivity, response lags, the treatment of risk and equity, economic and noneconomic impacts, the inclusion of potentially catastrophic losses, and discount rates. Aggregate estimates of costs mask significant differences in impacts across sectors, regions and populations and very likely underestimate damage costs because they cannot include many non-quantifiable impacts.

Limited and early analytical results from integrated analyses of the costs and benefits of mitigation indicate that they are broadly comparable in magnitude, but do not as yet permit an unambiguous determination of an emissions pathway or stabilisation level where benefits exceed costs.

Climate sensitivity is a key uncertainty for mitigation scenarios for specific temperature levels.

Choices about the scale and timing of GHG mitigation involve balancing the economic costs of more rapid emission reductions now against the corresponding medium-term and long-term climate risks of delay.

Summary of Synthesis Report here.

Heads up: I will be posting daily dispatches from Bali covering the final week of the COP-13 climate change negotiations (Dec. 10-14).