Climate myths that MUST go - Part II
This post is Part II of the post "Climate myths that MUST go". To read the previous post, go here:
Myth #2: Climate models are faulty because they are inequitable
This myth was brought to my attention in the same Twitter conversation as before. The tweet-er wrote:
"Also in AR6, the Scenarios assessed by IPCC especially the SSPs perpetuate inequalities going into the future. The IAMs are black boxes and the projections depict a screwed reality of the world by 2100."
They then led me to a podcast by the India Energy Hour, which further led me to an article on Carbon Copy.
Before I go any further, I'd like to state that I consider these to be generally good sources for climate articles/information. Thus, to me, the fact that these myths are surfacing on otherwise good platforms is a sign that there is a serious lack of communication between climate scientists and workers in climate justice / policy / communication.
The Carbon Copy article begins with an intriguing line:
"Its (IPCC's) climate models fail to reflect and preserve the principles of equity and rights to development while charting decarbonisation pathways."
This statement is essentially meaningless, because there is no place for equity, rights or development in the climate system. This is a hard pill to swallow and is based on two irrefutable, unchangeable scientific facts about nature:
(i) Carbon dioxide is a well-mixed gas. It does not matter where (which country) it is emitted. It has the same heat-trapping property wherever it comes from or goes to.
(ii) The only thing that matters is the concentration of carbon dioxide (and GHGs) in the atmosphere. It does not matter to the climate system whether emissions are due to x number of people, or 1000x, or x/1000 (you can add more zeros if you like).
The metrics of per capita emissions or national emissions do not matter to the climate system. The concepts of climate justice do not matter to the climate system. They do not matter to the Earth's atmosphere or oceans or land surfaces, etc etc. They do not matter to carbon dioxide and its heat-trapping property. They simply do not matter to nature. And since they do not matter to nature, they do not feature anywhere in climate models -- which are simply representations of nature.
These are incontrovertible scientific facts. If IPCC reports reflect such facts, it is not because the science is unequal. In fact, it is because the science is robust. Climate models faithfully represent the fact that nature does not care for man-made ideas of equality. (Please do not ridiculously extrapolate this statement to imagine that climate scientists do not care for equality. We do, because this man-made idea appeals to us as humans, even if it does not appeal to nature.)
Where does this mountain of confusion and resentment for climate models rise from? To begin to chip away at it, it is vital to understand the distinction between climate models (GCMs or ESMs) and integrated assessment models (IAMs). The former are based solely on principles of climate science. The latter links science with non-science concepts of society, economy, policies etc. Climate justice workers do not need to get a degree in climate science, but it is unacceptable and unhelpful to use these two terms interchangeably.
Irrespective of what other/developed nations are demanding from us, Indian workers can and should inform themselves of the climate model projections. These are based on robust and reliable science, but more importantly, they are unaffected by some shortcomings in IAM assumptions. I cannot understate the importance of this "independence", despite the caveat of "some" (which I will cover in a future blog post). Allow me to explain very, very briefly through a series of questions.
How does the IPCC make climate projections?
The IPCC does not carry out its own research. It only assesses and compiles results from published scientific literature till a set date to write the report. For AR6, this date was set as 31st January, 2021. So the report was based on published literature till then.
Who is the source of this "published literature"?
Various scientific modelling groups across the world, not restricted to any country or region, model the future based on common modelling standards. These standards are set down by CMIP, or the Coupled Modelling Intercomparison Project. CMIP hosts several MIPs -- all with the goal of providing multi-model answers to questions (as opposed to answers based on one or a few climate models only).
How do these modelling groups make these projections?
All projections are made using climate models. But climate models need some inputs, such as the concentration of greenhouse gases. Till AR5, the IPCC went with the "RCP" terminology. RCPs are Representative Concentration Pathways. They are potential future pathways for the concentration of greenhouse gases. Thus, every RCP gives a concentration for GHGs for each year in the future as input to the climate models. Remember, that is all the climate system cares for. And so this RCP-type input to climate models is sufficient for climate modellers to run future simulations, and answer the question -- how does the climate system respond to such-and-such GHG levels?
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| Source: Wikipedia |
For AR6, the IPCC "upgraded" this RCP approach to an SSP approach. SSPs are Shared Socio-economic Pathways. They are not a way of modelling the climate, but are a way of modelling societal decisions. But since it's the RCP information that actually matters to the climate system, all future scenarios are labelled with both SSP and RCP information. So CMIP (refer previous question) decided on 4 pathways for its "Tier 1" (most important) simulations:
SSP5-8.5 = SSP5 + RCP8.5
SSP3-7.0 = SSP3 + RCP7
SSP2-4.5 = SSP2 + RCP4.5
SSP1-2.6 = SSP1 + RCP2.6
(All this information is available on the page of ScenarioMIP -- the CMIP project that coordinates future climate modelling. Read Meehl et al., 2014 for a basic introduction to "Scenarios" on Page 2.)
What do these RCP + SSP combinations mean?
For example, SSP1-2.6. It means that we assume society will take decisions that lead to the RCP2.6 pathway shown in the picture above. Those decisions could be anything -- it does not matter to the climate system. But for the sake of policymakers, this set of decisions is itself modelled as the SSP1. Now policymakers can compare their actual decisions with these "assumed set of decisions" to get an idea of the impacts of their policies.
SSPs are not policy-prescriptive or binding on anyone. They are only modelling assumptions. And even if they are faulty, what eventually matter to the climate system and to the climate model projections are only the RCPs.
This brings me to the core message of this blog post:
It is wrong to dismiss climate projections based on shortcomings of IAMs.
And with that, I would like to call it a day. More in future blog posts, especially clarifications for some simplifications I have made in this post (which do not affect the message). Questions are welcome, the more "basic" (foundational), the better.
Myth #3: Climate system metrics = Other climate metrics →
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