- We are heading for 4.0°C increase in global temperature this century.
- Missing feedbacks in climate models mean this is an underestimate.
- The Committee on Climate Change aims to limit the likelihood of a 4°C increase to very low levels (e.g. less than 1%)
- The Committee on Climate Change recognises some of the missing feedbacks but does not include them in its assessment of the probability of dangerous climate change.
- They underestimate the probability of dangerous climate change by discounting important science.
The Emissions reduction pledges incorporated into the Cancun Agreements concluded last week fall short of the level of greenhouse gas emission reductions required to avoid dangerous climate change. No new pledges, beyond those associated with the Copenhagen Accord, materialized in Cancun, although the important step of incorporating those pledges into the framework of a UNFCCC agreement was taken. Climate Interactive’s Climate Scoreboard remains unchanged, showing that current pledges are more consistent with 4.0°C of temperature increase rather than the 2°C goal adopted in the Cancun Agreements.
There are positive feedback loops in the real climate system that are not modeled in the current version of C-ROADS. Additionally, C-ROADS is based upon and calibrated to the results of models from the IPCC’s Fourth Assessment Report. Recent science suggests that AR4 may underestimate the time-scale and magnitude of climate change. As a result, we believe that the Climate Scoreboard may well be presently a ‘best case’ interpretation of the long-term impacts of proposals on the table in the UNFCCC.
Dr Kevin Schaefer of the National Snow and Ice Data Centre has emailed to me (13 June 2011) on carbon feedback from thawing permafrost. He points out that important feedbacks are excluded from the ongoing round of the IPCC process (AR5). He says:
My estimates of carbon release from thawing permafrost are sound and the best available today. The measure of “soundness” is the 35% uncertainty, which is driven by uncertainty in the projected warming rate given a certain amount of fossil fuel emissions. As John Mitchell stated, four years ago the model teams decided not to include the permafrost carbon feedback in their IPCC AR5 projections due to the lack of data. We are making great progress, but the current round of simulations to support the IPCC AR5 do not include the permafrost carbon feedback. Nevertheless, we know enough now to recommend solid action.
If I were given the opportunity to talk to Chris Huhne, I would say
1. We must reduce total, global fossil fuel emissions.
2. None of the IPCC AR5 projections include the permafrost carbon feedback.
3. We must allocate 15% of total allowed global emissions to account for the permafrost carbon feedback.
4. The Department of Energy and Climate Change should definitely look into the permafrost carbon feedback because it implies a 15% greater reduction in fossil fuel consumption.
These feedbacks are worse if the released carbon were to contain a proportion of methane – a more powerful greenhouse gas than carbon dioxide. Dr Schaefer also says “It is true that thawing permafrost will release methane because of the large number of wetlands in the Arctic.”
There are other feedbacks not taken into account in the AR5 models. One example is the methane that is released from under the sea as methane ice disassociates due to warming oceans. The released methane can be consumed by marine plankton, preventing it from reaching the atmosphere. However, a recent paper (Elliott et al. ) shows that if enough methane ice disassociates, the methane would reach the atmosphere. Dr. Schaefer wrote (09 June 2011):
The Elliott et al.  paper is good solid research and should be taken seriously (I attached a copy for your records). They focused on ocean processes and did not estimate the surface methane fluxes over time that would be most useful to your work. However, they do show that the destruction of methane by marine plankton would saturate after a few decades such that methane released from melting methane ice would essentially end up in the atmosphere. A logical next step would be to apply their model under various IPCC scenarios to estimate methane fluxes to the atmosphere.
I think this paper changes the probability of initiating the methane ice feedback from “not sure” to “possible.” We need to quantify how much methane could be released from melting methane ice and when, with uncertainties. This paper demonstrates that the methane ice feedback can contribute to global climate change in the near future, clearly emphasizing the importance of “missing feedbacks” when developing global emission reduction strategies.
The Committee on Climate Change has emailed to me (13 June 2011) :
From reading the [Eliott] paper and Kevin Schaefer’s comments, I’m happy to go with his analysis: the study is a good contribution to developing our scientific understanding of methane clathrates in the ocean, but we have not yet reached the point where we have good estimates of what this might mean for future atmospheric fluxes.
This is one component of potential carbon release that is not incorporated into current climate model projections, along with those from thawing permafrost and wetlands. As such we’ll keep a watching brief on developments across these areas. I haven’t discussed the Elliott et al. paper specifically with Brian, although he may be aware of it from his own reading.
In their report of December 2010 the committee on Climate Change says
In our 2008 report ‘Building a low carbon economy – the UK’s contribution to tackling climate change’ we reviewed the scientific evidence on future climate risks. Based on that evidence we proposed a climate objective: to limit central estimates of global temperature increase by 2100 to as little above 2°C over pre-industrial levels as possible, and limit the likelihood of a 4°C increase to very low levels (e.g. less than 1%1). We assessed emissions pathways to meet this objective and concluded that global emissions of Kyoto greenhouse gases must peak by 2020, then decline rapidly so that they are halved by 2050, and continue to decline thereafter.
An email of 13 November 2009 from the Committee on Climate Change says:
On the subject of methane and climate feedback; we do not assign probabilities to methane release because we do not yet know enough about these processes to include them in our models projections. We do however draw attention to this in our ‘Building a Low Carbon Economy’ Report – December 2008.
In their 4th Carbon Budget, the Committee on Climate Change reference as supporting material a report which references the issues of missing feedbacks (28th March 2010):
The issue of natural methane release and climate models is indeed addressed in the AVOID report for the CCC, covering pp55-59.
Feedbacks acknowledged by the AVOID report are:
- methane emissions from wetlands
- substantial methane release from ocean hydrates.
- permafrost thawing releasing large amounts of additional carbon
The Committee on Climate Change acknowledges these feedbacks but still does not assign probabilities them. This is ignoring them. Because they ignore the effects of these important feedbacks, their proposals for limiting “the likelihood of a 4°C increase to very low levels” are seriously flawed.
Elliott et al. ,Marine methane cycle simulations for the period of early global warming
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