James Marett 4/1/2015

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Global Warming Potential (GWP) are the GHG gas multipliers for each type of gas that are used in computing the equivalent GHG effects for a specific gas to CO2 equivalents.

When I click on "effects" on top menu row, I see a dialogue window that displays the equivalent GWP factors for various types of gases for 20 year/100 year/ 500 year.

On the top row there is a button labeled "Apply IPCC GWP values".

There is also a comment on the same screen (bottom) that "it is recommended to use AR2 values for National Communications to the UNFCCC."

I believe based on IPCC guidance that this comment may be outdated. See (page 211 in the below... also attached)
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf

After updating the AR4 (AR FOUR, not AR2) the GWP values are correct and current based on IPCC guidance.

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Attachments:  UNFCCC GWP Decission.pdf [7]

Taylor Binnington 4/5/2015
 

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Thanks for the links, James! I think those are very useful. We'll have a discussion here about incorporating this into LEAP.

In the meantime, this is good information for anyone else with questions about which GWPs to use. Thanks!

Taylor

Charlie Heaps 4/5/2015
 

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A few further thoughts on this topic:

It is worth noting that the IPCC regularly updates GWP values, and indeed the values in the 4th Assessment Report (AR4) have now been superseded by those in the AR5 report. the 100 year GWP values for methane now distinguish between fossil and non fossil methane for example and have slightly higher values. The full set of values are available in Appendix 8a (P731) of Climate Change 2013: The Physical Science Basis. Available here:

https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

It is very important to note that for the purpose of reporting National Communications there is a need to be consistent across parties, so up until very recently the GWP values in the 2nd assessment report (AR2) have been recommended by the UNFCCC.

Note that LEAP does include the GWP values from AR1, AR2, AR3 and AR4 and you can switch among these from the General: Effects screen. We are planning on adding the values from the Fifth assessment report (AR5) in due course.

VERY IMPORTANT=============

It is my understanding that based on a decision made in 2013, the UNFCCC is now recommending that, as of 2015, all parties should use the AR4 values. In an upcoming release of LEAP I will therefore switch to use these as the default values. As James noted, you can in the meantime select these manually.

Please see this UNFCCC document that describes the decision to switch to the AR4 values in 2015:
http://unfccc.int/resource/docs/2013/cop19/eng/10a03.pdf

Note however that the UNFCCC's own web site has not yet been fully updated on this issue. See this for example:
http://unfccc.int/ghg_data/items/3825.php

I hope this helps,

Charlie