Explain xkcd: It's 'cause you're dumb.
Title text: 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.
|| This explanation may be incomplete or incorrect: Do a comparison of an increase of 1 IAU with the most recent IPCC predictions that where around when this comic was written in the explanation section|
If you can address this issue, please edit the page! Thanks.
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, so Randall points out that 4.5 °C is the difference between the last ice age and today. This is easy to see as a substantial difference. 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), and defines 0 as the modern temperature.
- -4 IAU is associated with Snowball Earth and is 4 IAU colder than the modern global temperature. Snowball earth is a near-total freezing of the entire surface around 650 millions years ago. How much of the planet was actually frozen in the Cryogenian period is disputed but it could have been the greatest ice age known to have occurred on Earth.
- -1 IAU is associated with the last ice age and is 1 IAU colder than now. During this time Randall's neighborhood was buried under an ice sheet.
- +1 IAU is the predicted change by the year 2100 and is 1 IAU warmer than now. We don't know what its effects will be exactly, that is why it is represented by a large question mark in the comic.
- +2 IAU is associated with the "Hothouse Earth" of the early Cretaceous period and is 1 IAU warmer than now. A increase of 4.5 °C (+1 IAU) seems like a small change in temperature. The magnitude of the change is more apparent when it is stated as "halfway to having palm trees at the poles" as there here were polar forests during the Cretaceous that grew in latitudes up to 85° in both Northern and Southern hemispheres.
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 temperature target.
The oldest known animal fossils (sponges) are from the Snowball Earth, while flowering plants became the dominant plant species during the Cretaceous period. It is believed that the entire Earth was frozen occurred 2,400 to 2,100 million years ago for the first time, which could have been a result of the Great Oxygenation Event.
The 200 m 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 Antarctica, IPCC Third Assessment Report (section 11.2.3 on Greenland and Antarctic Ice Sheets) and 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 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 Intergovernmental Panel on Climate Change (IPCC AR5) presents four alternative trajectories for future concentrations of greenhouse gasses, termed 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 (Working Group I Summary for Policymakers). This seems at odds with the 4-5 °C warming presented by Randall.
The lack of internationally binding agreements makes breaching an increase of 2 °C more and more likely.
- 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 0.25 on the scale and above it is written:]
- Where we are today
add a comment!
- [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
Scary thoughts there... 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? 188.8.131.52 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 IAU that named an 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. 184.108.40.206 07:33, 9 June 2014 (UTC)
- -- Fixed 220.127.116.11 (talk) (please sign your comments with ~~~~)
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 replaced it's nuclear power plants with coal ones ... -- 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 diagram on wikipedia. --18.104.22.168 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. -- Hkmaly (talk) 10:02, 10 June 2014 (UTC)
- While burning biomass adds CO2, the whole point of "burning a biologically-sourced fuel" like biodiesel is that you are merely returning to the atmosphere CO2 that was sucked out of the atmosphere by the biological material in the first place. So you grow an acre of plant material, and that acre of plant material sucks a certain amount of CO2 out of the atmosphere. When you then burn that plant material, you are releasing that CO2 back in to the atmosphere. Thus it is a "net zero" operation. While yes, it would be better to do a "net negative" operation (plant more plants while NOT releasing ANY CO2,) a net zero operation is still better than what we're doing now - releasing massive amounts of CO2 that have been locked up for geological-scale lengths of time, all in a VERY short timeframe. If you were to replace all work-generation power sources with "net zero" sources like biodiesel production and biomass generation, the levels of CO2 in the atmosphere would stop rising immediately. (Well, once they have reached equilibrium from other sources, anyway.) But of course, the difficulty is growing sufficient biological fuel material fast enough to create enough fuel for our needs. (The famous "it would take more farmland than currently exists on all of planet Earth, all of it dedicated to growing corn, to grow enough corn to make enough corn-derived ethanol to fuel every vehicle on the planet" problem.) So obviously energy efficiency and non-bio-fuel renewable energy methods are also needed. But biofuel (burning biomass, ethanol, biodiesel, etc,) is still a SIGNIFICANT improvement over oil/natural gas/coal. 22.214.171.124 07:31, 20 June 2014 (UTC)
Well, this seems like a topic that could generate heated comments. 126.96.36.199 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. 188.8.131.52 (talk) (please sign your comments with ~~~~)
- Cretaceous sea levels are generally accepted to have been 200m above the present level - you have large shallow seas (with geological evidence showing depths of 200m) over many of the continents - e.g. the Eromunga Sea in Australia. This is not from the IPCC, it predates that considerably. 184.108.40.206 11:35, 15 June 2014 (UTC)
- I hope the explanation isn't that he made a meter/feet mistake. 220.127.116.11 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. 18.104.22.168 (talk) (please sign your comments with ~~~~)
- 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. 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. 22.214.171.124 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? 126.96.36.199 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. 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. 188.8.131.52 17:01, 9 June 2014 (UTC)
So sad that Randall is pushing the carbon tax agenda long after the AGW myth has been debunked. 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.) 184.108.40.206 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.Seebert (talk) 19:28, 10 June 2014 (UTC)
- Randall is a scientist. He follows scientific consensus. 220.127.116.11 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.Seebert (talk) 19:28, 10 June 2014 (UTC)
- There is nothing scientific about following consensus. 18.104.22.168 (talk) (please sign your comments with ~~~~)
- 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. 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.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. -- 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.--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. 22.214.171.124 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... 126.96.36.199 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 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. 188.8.131.52 05:14, 10 June 2014 (UTC)
- It's hyperbole. 184.108.40.206 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. 220.127.116.11 12:18, 10 June 2014 (UTC)
- No, it's not hyperbole at all, actually there were tropical-climate trees in polar latitudes in the northern hemisphere during parts of the Cretaceous. 18.104.22.168 11:26, 15 June 2014 (UTC)
- Citation please- everything I could find was Temperate Rain Forests (kind of like still exist in Washington State and British Columbia).Seebert (talk) 12:28, 16 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. 22.214.171.124 (talk) (please sign your comments with ~~~~)
- I'd like to research that, so [needs citation]Seebert (talk) 17:22, 11 June 2014 (UTC)
- Things can be complicated by the likes of 'rebound' of the local area of the Earth's crust after the removal of the weight of glacial ice from various landmasses (although I'm not sure whether that was still producing such measureable effects to those particular locations in Roman times) and other effects. 126.96.36.199 11:07, 12 June 2014 (UTC)
- 1600-1700 years ago there were 6+ billion fewer people (a large proportion with dwellings near shorelines, or economically dependant on them somehow) on the planet! 188.8.131.52 11:38, 15 June 2014 (UTC)
According to the Scientific Forecasts from 1986, this should have had already happened by the year 2000: http://www.nytimes.com/1986/06/24/movies/earth-s-climatic-crisis-examined-by-nova.html 184.108.40.206
01:18, 28 June 2014 (UTC)