Most of the publications presented on this site originated in some way or the other from the application of one of the SiMCaP modules.

On the Risk of overshooting 2°C

by Malte Meinshausen, accepted at Scientific Symposium "Avoiding Dangerous Climate Change", MetOffice, Exeter, 1-3 February 2005

This article explores different greenhouse gas stabilization levels and their implied risks to overshoot certain temperature targets, such as limiting global mean temperature rise to 2°C above pre-industrial levels. The probabilistic assessment is built on a compilation of recently estimated uncertainties in climate sensitivity, which summarizes the key uncertainties in climate science for long-term temperature projections. The risk to overshoot 2°C equilibrium warming is found to lie between 68% and 99% for a stabilization at 550ppm CO2 equivalence. Only at levels around 400ppm CO2 equivalence, the risks of overshooting are limited so that the achievement of a 2°C target can be termed “likely”. Based on characteristics of 54 IPCC SRES and post-SRES scenarios, multi-gas emission pathways are presented that lead to a stabilization at 550, 450 and 400ppm CO2eq in order to assess the implications for global emission reductions. Sensitivity studies in regard to delayed global action show that the next 5 to 15 years might be decisive on whether the risk to overshoot 2°C can be limited to a reasonable range.

Multi-gas emission pathways to meet climate targets (EQW method)

by Malte Meinshausen, Bill Hare, Tom Wigley, Detlef van Vuuren, Michel den Elzen and Rob Swart, accepted for publication in Climatic Change, July 2005

So far, climate change mitigation pathways focus mostly on CO2 and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented method ‘Equal Quantile Walk’ (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission scenarios. The EQW method generates new mitigation pathways by ‘walking along equal quantile paths’ of the emission distributions derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO2 and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways are derived for stabilization at 350ppm to 750ppm CO2 concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a probabilistic multi-gas framework is demonstrated. The risk of overshooting a 2°C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the risk shall not be increased above 30%, it seems necessary to peak CO2 equivalence concentrations around 475ppm and return to lower levels after peaking (below 400ppm). EQW emissions pathways can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission control implications associated with certain climate targets.

How much warming are we committed to and how much can be avoided?

by Bill Hare and Malte Meinshausen, published as PIK-Report, October 2004

This paper examines different concepts of a ‘warming commitment’ which is often used in various ways to describe or imply that a certain level of warming is irrevocably committed to over time frames such as the next 50 to 100 years, or longer. We review and quantify four different concepts, namely (1) a ‘constant emission warming commitment’, (2) a ‘present forcing warming commitment’, (3) a ‘zero emission (geophysical) warming commitment’ and (4) a ‘feasible scenario warming commitment’. While a ‘feasible scenario warming commitment’ is probably the most relevant one for policy making, it depends centrally on key assumptions as to the technical, economic and political feasibility of future greenhouse gas emission reductions. This issue is of direct policy relevance when one considers that the 2003 global mean temperatures were 0.8°C above the pre-industrial mean and the European Union has a stated goal of limiting warming to 2°C above the pre-industrial mean: What is the risk that we are committed to overshoot 2°C? Based on the conventional IPCC uncertainty range for climate sensitivity (1.5°C to 4.5°C) and more recent estimates, we found that a (1) constant emission scenario is virtually certain to overshoot 2°C with a central estimate of 2.0°C by 2100 (4.2°C by 2400). (2) While for the present radiative forcing levels it seems unlikely (risk between 0% and 30%, central estimate 1.1°C by 2100 and 1.2°C by 2400), the risk of overshooting is increasing rapidly if radiative forcing is stabilized much above today’s levels (roughly 400ppm CO2 equivalence) in the long-term. (3) From a geophysical point of view, if all human-induced emissions were ceased tomorrow, it seems ‘exceptionally unlikely’ that 2°C will be overshoot (central estimate: 0.7°C by 2100; 0.4°C by 2400). (4) Assuming future emissions according to the lower end of published mitigation scenarios provides (350ppm CO2eq to 450ppm CO2eq) the central temperature projections are 1.5°C to 2.1°C by 2100 (1.5°C to 2.0°C by 2400) with a risk to overshoot of 10% to 50% by 2100 and 1%-32% in equilibrium. Furthermore, we quantify the ‘avoidable warming’ to be 0.16-0.26°C for every 100GtC of avoided CO2 emissions - based on a range of published mitigation scenarios.

Relationship between increases in global mean temperature and impacts on
ecosystems, food production, water and socio-economic systems

by Bill Hare, accepted at Scientific Symposium "Avoiding Dangerous Climate Change", MetOffice, Exeter, 1-3 February 2005

This paper attempts to associate different levels of global mean surface temperature increase and/or sea level rise with specific impacts and risks for species, ecosystems, agriculture, water and socio-economic damages compared to pre-industrial global mean temperature. It is found that that the risks arising from projected human induced climate change increase significantly and systematically with increasing temperature. Below a 1oC increase the level of risks are generally low but in some case not insignificant, particularly for highly vulnerable ecosystems and/or species. Above a 1oC increase risks increase significantly, often rapidly for highly vulnerable ecosystems and species. In the 1-2oC-increase range risks across the board increase significantly and at a regional level are often substantial. Above 2oC the risks increase very substantially involving potentially large numbers of extinctions or even ecosystem collapses, major increases in hunger and water shortage risks as well as socio-economic damages, particularly in developing countries.

by Malte Meinshausen, revised version of data appendix in F. Yamin and J. Depledge, "The International Climate Change Regime: A Guide to Rules, Institutions, and Procedures", Cambridge University Press, 2004

This appendix sets out information about Annex I Parties' GHG emissions, including whether each Party has achieved the 'stabilisation aim' under the UN Framework Convention on Climate Change and is likely to achieve its quantified commitments under the Kyoto Protocol. It also sets out such information for a number of Annex I Party groupings, such as Annex I, Annex II, the EU-15/25, Economies in Transition, and JUSSCANNZ. This version supersedes the one published in F. Yamin and J. Depledge, "The International Climate Change Regime: A Guide to Rules, Institutions, and Procedures", Cambridge University Press, 2004 (unfortunate production error).

by M.G.J den Elzen and M. Meinshausen (2005), in conference proceedings 'Non-CO2 Greenhouse Gases (NCGG-4), coordinated by A. van Amstel, Millpress, Rotterdam, ISBN 90 5966 043 9

This paper presents a set of multi-gas emission pathways compatible with different levels of ambition of avoiding long-term climate change, expressed in terms of different greenhouse gas concentration stabilization levels, i.e. 400, 450, 500 and 550 ppm CO2-equivalent. Also the effect of different assumptions on the resulting emission pathways, such as different baselines and technological improvement rates is analyzed. The emission pathways are derived using a methodology to calculate the cost-optimal implementation of available reduction options over the greenhouse gases, sources and regions. The emission pathway is determined iteratively to match prescribed climate targets of any level. Stabilizing greenhouse gas concentrations 450 CO2 equivalent or lower requires global emissions to peak within the next two decades, followed by substantial overall reductions by as much as 30 to 50% in 2050 compared to 1990 levels. Further delay in peaking of the global emissions leads to delayed, but much steeper reductions. The total emission reductions strongly depend on the emissions growth in the baseline scenario and the further improvements of the abatement potential and reduction costs for all greenhouse gases in the future.