Editing 1379: 4.5 Degrees
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==Explanation== | ==Explanation== | ||
− | This comic | + | {{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 he 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, although it is usually accepted as consisting of the greatest ice ages known to have occurred on Earth. | |
− | + | 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 (2ºC). 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. But it is unclear where his figure of 2°C comes from. The coolest of the most recent IPCC trajectories (RCP2.6) forecasts warming of only 0.3°C to 1.7°C in the year 2100. | |
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==Transcript== | ==Transcript== | ||
− | :Without prompt, aggressive limits on CO<sub>2</sub> emissions, the Earth will likely warm by an average of 4°-5°C by the | + | :Without prompt, aggressive limits on CO<sub>2</sub> emissions, the Earth will likely warm by an average of 4°-5°C by the century’s end. |
:'''HOW BIG A CHANGE IS THAT?''' | :'''HOW BIG A CHANGE IS THAT?''' | ||
:[A ruler chart is drawn inside a frame.] | :[A ruler chart is drawn inside a frame.] | ||
− | :In the coldest part of the last ice age, | + | :In the coldest part of the last ice age, Earth’s average temperature was 4.5°C below the 20<sup>th</sup> 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:] | :[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 | :-2 IAU -1 IAU 0 +1 IAU +2 IAU | ||
− | :[Next to the 0 marking a black arrow points toward 0. | + | :[Next to the 0 marking a black arrow points toward 0.2 on the scale and above it is written:] |
:Where we are today | :Where we are today | ||
Line 59: | Line 49: | ||
:Cueball: Hi! | :Cueball: Hi! | ||
:[Below +1 IAU a black arrow point toward this division. Below the arrow is written:] | :[Below +1 IAU a black arrow point toward this division. Below the arrow is written:] | ||
− | :Where | + | :Where we’ll be in 86 years |
:[Below this a white image. At the top of the image is written:] | :[Below this a white image. At the top of the image is written:] | ||
:My neighborhood: | :My neighborhood: | ||
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:No glaciers | :No glaciers | ||
:Palm trees at the poles | :Palm trees at the poles | ||
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{{comic discussion}} | {{comic discussion}} | ||
+ | [[Category:Comics featuring Cueball]] | ||
[[Category:Comics with color]] | [[Category:Comics with color]] | ||
[[Category:Charts]] | [[Category:Charts]] | ||
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