explain xkcd - User contributions [en]

Talk:1379: 4.5 Degrees

2014-06-11T07:55:43Z

Ojdo: against: "pushing" carbon tax

Scary thoughts there... [[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 05:11, 9 June 2014 (UTC)

I imagine the Earth's axial tilt wouldn't change even if the temperature changed by +2 IAU. So, would palm trees survive the extreme day/night lengths at the poles? [[Special:Contributions/103.22.201.239|103.22.201.239]] 05:31, 9 June 2014 (UTC) P.S. Also, wouldn't the North Pole be underwater, so incapable of supporting palm trees?
Also, regarding the IAU, is it a reference to the {{w|International Astronomical Union|IAU}} that named an {{w|4942 Munroe|asteroid}} after Randall?

"While it says it's "probably no big deal," this is probably a joke, because even half of an Ice Age would be a lot of ice." The article has it wrong. It's a 2 degree increase, not decrease. Ice would melt. [[Special:Contributions/108.162.238.134|108.162.238.134]] 07:33, 9 June 2014 (UTC)
:-- Fixed {{unsigned ip|173.245.54.77}}

To prevent global warming, act yesterday! ... or, well, since we already failed to do it, maybe ... just maybe ... we should invest some resources to ADAPTING to the change. Because the USSR communist party wanted to command “wind and rain” and how it worked?
... of course, we SHOULD be trying to lower the CO2 emissions ... not like Germany, which [http://www.realclearenergy.org/charticles/2014/01/16/germanys_plans_for_new_coal_plants_107463.html replaced it's nuclear power plants with coal ones] ... -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 10:03, 9 June 2014 (UTC)
:While it is true that we have build more coal plants, the majority part that replace the nuclear power is from renewable energy, see [https://de.wikipedia.org/wiki/Strommix#mediaviewer/Datei:Energiemix_Deutschland.svg diagram] on wikipedia. --[[Special:Contributions/141.101.75.89|141.101.75.89]] 15:51, 9 June 2014 (UTC)
:: ... note that burning biomass, while renewable, also adds CO2. Not speaking about oil. You shouldn't be closing nuclear plants, you should be closing coal ones if you have exceed energy. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 10:02, 10 June 2014 (UTC)

Well, ''this'' seems like a topic that could generate heated comments. [[Special:Contributions/108.162.208.9|108.162.208.9]] 10:09, 9 June 2014 (UTC)

Would anyone care to comment on the +200 meter sea rise? I googled "how much would sea level rise" a bit, and I seem to bump into 60 to 70 meters repeatedly for all glaciers melting. I found nothing direct from IPCC. I wonder if Randall really has another view on this. {{unsigned ip|108.162.254.45}}
:I hope the explanation isn't that he made a meter/feet mistake. [[Special:Contributions/103.22.201.239|103.22.201.239]] 13:04, 9 June 2014 (UTC)
::I would assert that he rounded for a clean read for a relative scale. Also, the '+' denotes the likelihood of a larger actual amount. {{unsigned ip|108.162.217.41}}
:::60 meters is indeed the amount the sea would rise if all the glacial ice melted. However, that figure presumably does not take into account have much the sea would rise by expansion due to the increased heat. That is, after all, the main reason for rising sea levels today. So I would guess that the +200 figure is the 60 meters of added water from glacial ice ''plus'' the amount it would rise due to warming and expanding. [[User:Calebxy|Calebxy]] ([[User talk:Calebxy|talk]])
::::While that's possible, and desalination of water can also cause it to expand (sea water is more dense than fresh), we shouldn't try to justify the numbers if they are incorrect. If we can find some reliable data to suggest the rise would be 200 ft instead of 200m, we should include that. Or at least include a range of estimates from reliable sources. [[Special:Contributions/108.162.238.134|108.162.238.134]] 15:42, 9 June 2014 (UTC)
:::::Having just re-read the explanation after posting my comment, I can see that the article attempts to do just that. But the link provided says 110 to 770 mm. Isn't the millimeters? [[Special:Contributions/108.162.238.134|108.162.238.134]] 15:44, 9 June 2014 (UTC)
:::::But the sea level ''would'' rise more than 60m if the expansion of the sea is taken into account. If the earth became as hot as the graph indicates, then logically the seas would expand considerably. [[User:Calebxy|Calebxy]] ([[User talk:Calebxy|talk]]) 16:04, 9 June 2014 (UTC)
:Cretaceous sea levels seem to have been that high, but this tends to be attributed to the shape of the ocean basins, in particular the mid-ocean ridges, rather than to the temperature. [[Special:Contributions/108.162.219.35|108.162.219.35]] 17:01, 9 June 2014 (UTC)

So sad that Randall is pushing the carbon tax agenda long after the AGW myth has been debunked. [[User:IGnatius T Foobar|IGnatius T Foobar]] ([[User talk:IGnatius T Foobar|talk]]) 16:00, 9 June 2014 (UTC)
:Waitwhat? a) I saw no mention of tax. b) AGW==Anthropogenic Global Warming==debunked? This may not be the place for this whole discussion (despite the relevance), but it's ''far'' from debunked. And even if "there was going to be some Global Warming anyway", you can't dismiss the probability that we're adding ''something'' to this effect and making it more extreme. If not pushing it over the edge in some way. (I'm actually more optimistic than that, but I do find "it's a myth!" to be annoyingly naive, so excuse me if I try to balance that out. It's really not worth tying this discussion box up in this debate, however.) [[Special:Contributions/141.101.98.232|141.101.98.232]] 18:36, 9 June 2014 (UTC)
::I'm not as sure that it isn't worth it. GCC is fact. GW, might be. AGW, that's where we get into the mythical and unproven range, because it's *really hard* to tell the difference between correlation and causation, and because of other problems I wrote below.[[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 19:28, 10 June 2014 (UTC)
:Randall is a scientist. He follows scientific consensus. [[Special:Contributions/108.162.238.134|108.162.238.134]] 20:03, 9 June 2014 (UTC)
::Randall is a comic artist. While he's a really smart guy, he popularizes science, he doesn't do the experiments himself.[[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 19:28, 10 June 2014 (UTC)
::There is nothing scientific about following consensus. {{unsigned ip|108.162.215.86}}
:::Of course there is... When 99% of climatologists are reasonably certain (which means "very very sure" for non-scientists) that there is Global Warning and that the primary cause is us (humanity greenhouse gas emissions), I wouldn't say that AGW has been "debunked" and that there is nothing scientific in following this consensus (after having made sure of its existence by reading diverse peer-reviewed studies of the field) ! You may have an agenda to defend but could you at least try to make some sense, please. Note that this doesn't mean that the current political propositions are the right way to go about it and that this comic doesn't say anything about that. [[User:Jedaï|Jedaï]] ([[User talk:Jedaï|talk]]) 21:47, 9 June 2014 (UTC)
::::And this is why climatologists playing with models instead of actually examining data from the real world, aren't scientists. It's possible to get so addicted to your models, that you fail to realize that you've fallen into confirmation bias. And consensus, also known as mob-based peer pressure, is only as smart as the lowest IQ in the mob. Which is why climatologists, attempting to top each other's predictions, have a tendency to fall for worst case scenarios, such as Randall's scenario above.[[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 02:42, 10 June 2014 (UTC)
::::There really ISN'T anything scientific about following consensus. Correlation is not causation. The 99% figure will be scientifically relevant if it will be produced by every scientist independently proving it, not by consensus. And even then ... 100% scientists though time is same everywhere ... then Einstein came with theory and models ... and THEN the models were verified. By Sir Arthur Eddington four years later. THAT made Einstein famous. We don't really have the same kind of proof for AGW. We have lot of data which has been tampered with or cherry-picked, even the scientists can't be sure what to believe. What we DO have proof for is that climate is changing (although some of those changes are LOWERING of temperature).
::::And about the political propositions ... most of them fail to reduce the greenhouse gas emissions itself, not speaking about global temperature - but their economic effect would be huge. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 10:02, 10 June 2014 (UTC)
:Where is he speaking about carbon tax? "Acting now" does not equal one possible instrument. There are plenty of ways for climate change mitigation.--[[User:Ojdo|Ojdo]] ([[User talk:Ojdo|talk]]) 07:55, 11 June 2014 (UTC)

I *think* (haven't confirmed) that the 200 m figure is the difference between the peak of the last ice age (sea level low—"-1 IAU" in the strip) and if everything melted. We've already come up 140 m, so we can't go up 200 m from here. [[Special:Contributions/108.162.215.86|108.162.215.86]] 20:16, 9 June 2014 (UTC)

There are several troubling things with this comic (including the sea level figure), but the most basic is the opening statement: "Without prompt, aggressive limits on CO2 emissions, the Earth will likely warm by an average of 4°-5°C by the century’s end." This is probably from the latest IPCC report, but it takes the worst of several proposed scenarios, and claims it to be the likely one. RCP8.5 projects 2.6C-4.8C, and I suppose that's what getting averaged *up* to "4.5C" for the temperature line in the comic. The second most troubling thing is that mouse-over text, regarding the 2C lid if we "enact aggressive emissions limits now"—this is an entirely arbitrary (unscientific) number based on largely unspecified changes to what the world is doing now. It gives me the sense that Randall didn't look too deep... [[Special:Contributions/108.162.215.86|108.162.215.86]] 20:43, 9 June 2014 (UTC)

According to Wikipedia, the polar forests during the Ceretaceous period were temperate, not tropical. Thus Firs in the North and Evergreens in Antartica, not Palm trees. http://en.wikipedia.org/wiki/Polar_forests_of_the_Cretaceous [[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 21:17, 9 June 2014 (UTC)

Oh wait, did he really say "Palm trees at the poles"? The north pole is already 4,261 meters under water. The nearest land is 700 km away. [[Special:Contributions/108.162.215.86|108.162.215.86]] 05:14, 10 June 2014 (UTC)
:It's hyperbole. [[Special:Contributions/108.162.238.134|108.162.238.134]] 05:46, 10 June 2014 (UTC)
::Not completely. It's refering to a specific time, the ceretaceous period. When there where forests above 85 degrees in both north and south poles. The forests where temperate though, so palm trees are hyperbole. [[Special:Contributions/141.101.80.217|141.101.80.217]] 12:18, 10 June 2014 (UTC)

Independent of everything else, I'm having a tough time reconciling the fact that sea level was apparently 6m or more higher during the Roman era. E.g. the roman settlements and their harbors in places like Caister and Burgh Castle in Norfolk, England? I'm not aware that England has risen 6m. Seems to me that if see levels were to rise as much as 6m we'd just be back to where things were 1600-1700 years ago.

1379: 4.5 Degrees

2014-06-11T07:49:43Z

Ojdo: /* Explanation */ added reason for 2 °C in the title text

{{comic
| number = 1379
| date = June 9, 2014
| title = 4.5 Degrees
| image = 4_5_degrees.png
| titletext = The good news is that according to the latest IPCC report, if we enact aggressive emissions limits now, we could hold the warming to 2°C. That's only HALF an ice age unit, which is probably no big deal.
}}

==Explanation==
{{Incomplete|Do a more careful comparison of Randall's presented predictions with the most recent IPCC predictions}}
This comic is a way to visualize changes in climate over the next century. The prediction presented, 4-5 degrees Celsius of warming, doesn't seem like a very large change, but [[Randall]] points out that 4.5 °C is the difference between the {{w|Last glacial period|last ice age}} and today, which is quite a substantial difference. So, to give context to the number, he measures the temperature in "Ice Age Units," or IAU. 1 IAU is defined as the change in average global temperature by 4.5 degrees Celsius (8 °F). The last ice age was 1 IAU colder than the average "modern" {{w|global temperature}}, and Randall's neighborhood was buried under an ice sheet. The predicted change by the year 2100 is +1 IAU, and while we don't know what its effects will be exactly (represented by a large question mark in the comic) it will probably be huge. For reference he notes that a change of +2 IAU created the {{w|Cretaceous Thermal Maximum|"Hothouse Earth"}} of the early {{w|Cretaceous period}}. In short, while 4.5 °C seems like a small change in temperature, it seems quite a lot bigger if you phrase it as "halfway to having {{w|Arecaceae|palm trees}} at the poles." There were {{w|Polar forests of the Cretaceous|polar forests}} during the Cretaceous that grew in latitudes up to 85° in both Northern and Southern hemispheres. Of course there could not be trees in the ocean directly over the North Pole, but at the closest land masses ({{w|Greenland}} for instance) there could be trees.

On the colder side, -4 IAU is associated with {{w|Snowball Earth}}, a near-total freezing of the entire surface. How much of the planet was actually frozen in the {{w|Cryogenian}} period is disputed but it could have been the greatest ice age known to have occurred on Earth. The mean temperature must have lowered to a level of 15 to 20 °C below actual values roughly a billion years in the past.

The oldest known animal fossils ({{w|Sponges#Fossil_record|sponges}}) are from the Snowball Earth, while {{w|Flowering_plant#Evolution|flowering plants}} became the dominant plant species during the Cretaceous period.

The 200 m {{w|Current sea level rise|sea level rise}} given in the last panel for a "Cretaceous Hothouse" (i.e. if all ice on earth melted, including the Antarctic ice cap) could not be explained by this melt-off alone. If all the ice melted the water level would only increase by about 60-80 m, according to {{w|Antarctica}}, [http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/ IPCC Third Assessment Report] (section 11.2.3 on Greenland and Antarctic Ice Sheets) and [http://water.usgs.gov/edu/sealevel.html Sea Level and Climate: USGS Water-Science School]. Additional sea level rise can be expected from thermal expansion of seawater, and indeed the main reason for rising sea level at the moment is actually caused by this expansion of the sea due to increasing temperature. But the high-end 500-year projection for a 4x increase in CO2, at {{w|Current_sea_level_rise#IPCC_Third_Assessment|expansion of the sea}}, is for an additional 2 m due to thermal expansion, with a decreasing rate of growth over time.

The 5th and most recent {{w|Intergovernmental Panel on Climate Change}} (IPCC AR5) presents four alternative trajectories for future concentrations of greenhouse gasses, termed {{w|Representative Concentration Pathways}} (RCPs): RCP2.6, RCP4.5, RCP6, and RCP8.5. They are named after possible ranges of radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively). The hottest of these, RCP8.5, is predicted to result in a warming of 2.6 °C to 4.8 °C by 2100 ([http://www.climate2013.org/images/report/WG1AR5_SPM_FINAL.pdf Working Group I Summary for Policymakers]). This seems at odds with the 4-5 °C warming presented by Randall.

The title text says that even with instant and aggressive emissions reduction, the temperature will still rise by roughly half an IAU (2 °C). While it says it's ''probably no big deal'', this is a joke, because even the equivalent of half an Ice Age Unit of warming would cause a huge climate change. The figure of 2 °C is the most commonly agreed {{w|Climate_change_mitigation#Temperature_targets|temperature target}}; however, the lack of internationally binding agreements makes breaching this target more and more likely.

==Transcript==
:Without prompt, aggressive limits on CO2 emissions, the Earth will likely warm by an average of 4°-5°C by the century’s end.
:'''HOW BIG A CHANGE IS THAT?'''

:[A ruler chart is drawn inside a frame.]
:In the coldest part of the last ice age, Earth’s average temperature was 4.5°C below the 20th century norm.
:Let’s call a 4.5°C difference one '''”Ice age unit.“'''

:[A ruler with five main divisions — each again with 3 smaller quarter division markers. Above it the five main divisions are marked as follows with 0 in the middle:]
:-2 IAU -1 IAU 0 +1 IAU +2 IAU
:[Next to the 0 marking a black arrow points toward 0.2 on the scale and above it is written:]
:Where we are today

:[The rest of the text is below the ruler.]
:[To the far left below -2 IAU a curved arrow points to the left. Below it is written:]
:Snowball earth (-4 IAU)
:[Below -1 IAU a black arrow point toward this division. Below the arrow is written:]
:20,000 years ago
:[Below this an image of a glacier. At the top of the image is written:]
:My neighborhood:
:[At the bottom of the image is an arrow pointing to the glacier:]
:Half a mile of ice
:[Below 0 IAU a black arrow point toward this division. Below the arrow is written:]
:Average during modern times
:[Below this an image of Cueball standing on a green field with a city skyline in the background. At the top of the image is written:]
:My neighborhood:
:Cueball: Hi!
:[Below +1 IAU a black arrow point toward this division. Below the arrow is written:]
:Where we’ll be in 86 years
:[Below this a white image. At the top of the image is written:]
:My neighborhood:
:[Below this is a very large:]
:'''?'''
:[Below +2 IAU a black arrow point toward this division. Below the arrow is written:]
:Cretaceous hothouse
:+200m sea level rise
:No glaciers
:Palm trees at the poles

{{comic discussion}}

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