IPCC report on global warming (of Oct.2018)

See the main “No planet B” page if you don’t know what the IPCC is and does. You can find a summary of the report I’ll talk about here, Since I’m guessing most of you won’t really click on the link (I don’t blame you, it’s not exactly a Tolkien-style reading). Here are some excerpts, which I found interesting. The report is based on predictions made by the most advanced climate change models available, so while I assume they are accurate, they are not the absolute truth (but may be very close to it).
The report is subdivided into
A. what is global warming of 1.5°C
B. what do models predict about the consequences of such warming
C. what do we need to do on global level to keep the warming below 2°C by 2030
D. do the current regulations on emissions grant that we keep the warming below 1.5°C by 2050?

Some of it can be used when confronted with the “climate change has always happened and human activity didn’t cause it”-argument. Several terms used in the quotes are technical, but they created a glossary, where they explain the terms such that even a Labrador would understand. Also, sometimes the likelihood of an outcome or a result is mentioned, here is how to read it (you can find it in FN3 in the introduction on this link here):
virtually certain 99–100%,
very likely 90–100%, likely 66–100%,
about as likely as not 33–66%,
unlikely 0–33%,
very unlikely 0–10%,
exceptionally unlikely 0–1%.
Additional terms (extremely likely 95–100%, more likely than not >50–100%, more unlikely than likely 0–<50%, extremely unlikely 0–5%)

Note on probability in IPCC: I’ll try to dig deeper into the whole construct of probability the IPCC has. It doesn’t seem so easy but I’ll add the link to that here when I’m done.


What are we talking about

“A.1. Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.2°C. Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate. (high confidence).”

Note: ‘Present level of global warming’ is defined as the average of a 30-year period centred on 2017 assuming the recent rate of warming continues.

In A.1. essentially they are stating an estimation of the contribution of human activity to the increase in global warming (it’s approx. 0.8 to 1.2°C). What are the consequences of anthropogenic emissions (that is emissions caused by human activity) from the pre-industrial period until today?

“A.2. Warming from anthropogenic emissions from the pre-industrial period to the present will persist for centuries to millennia and will continue to cause further long-term changes in the climate system, such as sea level rise, with associated impacts (high confidence), but these emissions alone are unlikely to cause global warming of 1.5°C (medium confidence).”

Basically there is medium confidence in the statement that emissions caused by human activity from pre-industrial to present time alone will NOT cause a warming of 1.5°C. In other words, I guess this means that there is average confidence that emissions caused by humans in the time period mentioned will cause further global warming up to 1.5°C.

The consequences

“B.1. Climate models project robust differences in regional climate characteristics between present-day and global warming of 1.5°C, and between 1.5°C and 2°C. These differences include increases in: mean temperature in most land and ocean regions (high confidence), hot extremes in most inhabited regions (high confidence), heavy precipitation in several regions (medium confidence), and the probability of drought and precipitation deficits in some regions (medium confidence).”

“B.5. Climate-related risks to health, livelihoods, food security, water supply, human security, and economic growth are projected to increase with global warming of 1.5°C and increase further with 2°C.”

The basic idea is that the mean temperature in most regions of the world will rise (be aware that the objection “it snowed today in London so global warming is a lie” doesn’t really apply for the mean says little about the weather in a particular point in time and place. It will also rain a lot (precipitation) in some regions and in others there will droughts (think of California and all the drought issues there). Should we reach an increase of 1.5°C, then consequences will, amongst others, affect our health, water and food supply.

How much emission will keep us under an increase of 1.5°C by 2030?

“C.1. In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range). […]

In order to keep increase lower or equal to 1.5°C, we will need to decrease carbon dioxide emissions by 45% from the levels reported in 2010.

“C.2. Pathways limiting global warming to 1.5°C with no or limited overshoot would require rapid and far-reaching transitions in energy, land, urban and infrastructure (including transport and buildings), and industrial systems (high confidence). These systems transitions are unprecedented in terms of scale, but not necessarily in terms of speed, and imply deep emissions reductions in all sectors, a wide portfolio of mitigation options and a significant upscaling of investments in those options (medium confidence).”

To limit warming to 1.5°C we need to change the way we produce and utilise energy and need to transit to sustainable industrial and infrastructural (transport and buildings) systems, such that emissions can be consistently reduced.

Part D.
Do the realisations of current environmental promises (=mitigation ambitions) grant that we do not exceed the warming by 2030?

“D.1. Estimates of the global emissions outcome of current nationally stated mitigation ambitions as submitted under the Paris Agreement would lead to global greenhouse gas emissions in 2030 of 52–58 GtCO2eq yr1 (medium confidence). Pathways reflecting these ambitions would not limit global warming to 1.5°C, even if supplemented by very challenging increases in the scale and ambition of emissions reductions after 2030 (high confidence). […].”

During the Paris Agreement some nations committed themselves to so-called mitigation ambitions, i.e. environmental promises. These mitigation ambitions do not suffice, according to the models, to limit global warming to 1.5°C by 2030, even if new and strict mitigation ambitions shall be committed to in the next years.

This is basically it. Here are some core concepts, which are good to know:

Pre-industrial is the period (several centuries) prior to the onset of large-scale industrial activity around 1750.

Global mean surface temperature (GMST) is an estimation of the “global average of near-surface air temperatures over land and sea ice, and sea surface temperatures over ice-free ocean regions […].”


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